Welcome to The Weather Report

Welcome to The Weather Report Are you a pilot or CFI interested in gaining a deeper understanding about aviation weather? Do you want to get beyond a standard briefing from Lockheed Martin Flight Services or DUATS? Got a burning question about a weather topic? Want to ask a question about a workshop? Or just want to learn more about aviation weather? Post it here. Not a member of AvWxWorkshops.com? Become a regular member or elite member now and start enjoying the unique benefits this site has to offer. <strong>Note: You must be a paid Member or Elite Member to view and post messages in these discussion forums</strong>. http://avwxworkshops.com/forum/index.php Wed, 08 Sep 2010 08:29:30 -0400 Phorum 5.2.7 http://avwxworkshops.com/forum/read.php?8,237,237#msg-237 Very nice simulated reflectivity image of hurricane Earl (no replies) http://avwxworkshops.com/forum/read.php?8,237,237#msg-237

http://avwxworkshops.com/forum/file.php?8,file=87,filename=Sim-Reflect-Earl.gif

]]> Scott Dennstaedt Scott's Aviation Weather Blog Wed, 01 Sep 2010 08:20:29 -0400 http://avwxworkshops.com/forum/read.php?8,233,233#msg-233 GFS model has been upgraded! (no replies) http://avwxworkshops.com/forum/read.php?8,233,233#msg-233 announcement.

Quote:
These improvements include an upgraded radiation and cloud package, upgraded specification of gravity wave drag, a higher resolution grid for hurricane relocation, an upgraded boundary layer scheme, the use of a higher resolution snow analysis, a new mass flux shallow convection scheme and an updated deep convection scheme. Also, the model will have a horizontal resolution of 27 km through 192 hours in support of the GFS MOS development, which is an additional 12 hours from the previous version. The model’s resolution from 192 to 384 hours will remain at 70 km. Finally, the availability of three hourly forecast output will be extended out to 192 hours from 180 hours.

Here's the official Technical Implementation Notice for this upgrade.]]> Scott Dennstaedt Scott's Aviation Weather Blog Sun, 15 Aug 2010 16:38:06 -0400 http://avwxworkshops.com/forum/read.php?8,232,232#msg-232 New version of Aviation Weather Services is now available! (no replies) http://avwxworkshops.com/forum/read.php?8,232,232#msg-232 here, but you are probably better off with a complete document that I've made available here. The single biggest change is the addition of G-AIRMETs which were made operational on October 1, 2009. Click here to learn more about G-AIRMETs.]]> Scott Dennstaedt Scott's Aviation Weather Blog Thu, 05 Aug 2010 09:18:14 -0400 http://avwxworkshops.com/forum/read.php?8,226,226#msg-226 Response to J. Mac McClellan's recent Left Seat article (2 replies) http://avwxworkshops.com/forum/read.php?8,226,226#msg-226
Most writers (that are also pilots and/or instructors) that don't have a background in meteorology really have very little hope to get it right. So you have to be extremely careful trying to read these articles hoping to glean some wisdom that you can believe in. Mac's Left Seat article is a perfect example of an article that just rambles on with typical pilot nonsense...

The article (not available on the web yet) discusses his trip on a crappy day in mid-May. While he didn't mention the specific date in his article, I was able to deduce through some trial and error weather forensics that his flight was on May 12th. He was attempting to fly from Westchester County (north of New York) to Wichita, Kansas. First of all, someone needs to teach Mr. Mac about a phenomenon called Mesoscale Convective Systems (MCSs).

In the morning, he noticed that there was a fairly widespread area thunderstorms over southwestern Ohio, southern Indiana and southern Illinois as can be seen on this 15Z surface analysis/radar composite. This feature is called a mesoscale convective system or MCS.

http://avwxworkshops.com/forum/file.php?8,file=79,filename=15Z-Radar-Composite.gif

He goes onto say, "Often these lingering nocturnal storms dissipate by midmorning." That's the first clue he's never heard of an MCS. MCSs are a "special" organization of thunderstorms that develop in a rather benign-looking weather regime (more on that later). They are nocturnal (may develop in the late afternoon and continue through the night), but will often persist well into the next day as they trek across the country relatively quickly. It is not unusual for them to be maintained throughout a 24 hour period.

All he had to do is pull up the Storm Prediction Center's mesoscale discussion for the morning and he would have been more informed of what was about to occur in this area.

http://avwxworkshops.com/forum/file.php?8,file=80,filename=mcd0525.gif

MESOSCALE DISCUSSION 0525
NWS STORM PREDICTION CENTER NORMAN OK
0916 AM CDT WED MAY 12 2010

AREAS AFFECTED...ERN KY...EXTREME SRN KY THROUGH SRN WV

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 121416Z - 121615Z

THREAT FOR ISOLATED DAMAGING WIND AND HAIL EXPECTED TO INCREASE
THROUGH THE MORNING INTO THE AFTERNOON. TRENDS ARE BEING MONITORED
FOR A POSSIBLE WW.

QUASI-STATIONARY FRONT EXTENDS FROM NRN WV THROUGH SRN OH...SRN IND
AND IL. AN MCS CONTINUES FROM SRN IND...NRN KY AND SRN OH. BOUNDARY
LAYER WILL UNDERGO DESTABILIZATION THROUGH THE MORNING...BUT WILL BE
MITIGATED SOMEWHAT BY EXTENSIVE CONVECTIVE DEBRIS. THE LATEST
OBJECTIVE ANALYSIS SHOWS A RESERVOIR OF 1000 MLCAPE IN WARM SECTOR.
A 40 KT WSWLY LOW-LEVEL JET WILL MIGRATE EWD THROUGH NRN KY IN
ASSOCIATION WITH A PROGRESSIVE MCV LOCATED OVER ERN IL. THE
LOW-LEVEL JET WILL MAINTAIN FEED OF HIGHER THETA-E AIR INTO THE
MCS...AND STORMS WILL LIKELY INTENSIFY AS THE ATMOSPHERE
DESTABILIZES. UNIDIRECTIONAL 40-45 KT DEEP SHEAR WILL SUPPORT
POTENTIAL FOR ORGANIZED STORMS. GREATEST THREAT FOR DAMAGING WIND
WILL LIKELY BE WITH NE-SW ORIENTED LINE OF STORMS ALONG THE WRN END
OF THE MCS. ACTIVITY COULD BUILD A LITTLE FARTHER SWD AS MCS
CONTINUES EWD. VERY HEAVY RAIN AND POSSIBLY SOME HAIL WILL REMAIN
LIKELY WITH E-W BAND OF STORMS DEVELOPING ON THE WARM ADVECTION
WING.

While the discussion above is quite technical, it does imply that a severe thunderstorm watch is possible and that these storms are not going to dissipate anytime soon. As also mentioned in the discussion, these systems can produce a lot of convective debris making a flight under IFR quite challenging without the proper real-time equipment installed and operational.

He then says, "The winds-aloft forecast should have told me this was not going to be an ordinary thunderstorm day. At 6,000 feet the forecast called for westerly winds greater than 50 knots, and at 9,000 feet higher than 60 knots. That is a very powerful wind for May and should have told me how much energy this storm system still contained."

Well...just goes to show you he's still living in the 80s and 90s. The FB Winds are outdated and should be retired. There are many other products that provide a much better spatial and temporal resolution. In early to mid-May it is not uncommon for the flow to still be rather active. A 50 or 60 knot wind at these altitudes are not unusual. Turns out the actual winds were more like 40 - 50 knots at these altitudes. I'll get back to the upper level flow shortly.

I'm not sure why, but this next discussion from Mac floored me. He said, "Unlike Richard Collins, who spent his flying life studying the big weather picture and writing about it in these pages, I usually don't pay much attention to the location of fronts and lows and highs. With Nexrad in the cockpit, I can dial the range out across the country and see what's there, no matter what the surface prognostic chart shows for fronts and lows....I can see the latest conditions during flight, so I don't really wonder what big weather factor is causing what is taking place."

Really? He ignores this other valuable information because he doesn't understand how to take advantage of it. Or he simply has a lazy attitude about preflight planning. His crude method is to react to what he sees outside the cockpit or he uses his satellite weather Nexrad display and makes up the plan as he goes. Really?

Well, to be fair, he then goes onto say, "This time I should have paid more attention to the big picture. The surface chart had a stationary front stretching west to east more than 1,500 miles, which is unusually long for a continuous front. The front originated in western Colorado and went out intot he Atlantic at New Jersey. There were four pretty deep lows spaced across the front with one high pressure center also on the front in West Virginia. I don't know how a high formed there, but it should have told me this was no ordinary system."

Well, Mac did a pretty good job describing the 18Z surface analysis below. A long stationary front like this is not unusual. There was an even longer continuous front stretching the entire country on May 6 and another one on April 23. Mac just doesn't look at these features as he freely confessed. These areas of low pressure were not all that deep. The standard atmosphere is 1013 mb and the lows along this front were 1010 mb, 1014 mb and two 1002 mb. For this time of year, they were not exceptionally deep.

http://avwxworkshops.com/forum/file.php?8,file=82,filename=18Z-CONUS.gif

The high pressure in West Virginia that he mentions also shows his ignorance. Now, I admit that most pilots don't understand this next point, but if you are going to write about this stuff, at least ask someone who knows before you plead ignorance. The high in West Virginia is called a cold pool high. If he would have noticed, the MCS had moved east and was positioned right over West Virginia at 18Z as can be seen below. Near the surface, the MCS exhibits high pressure, with an outflow boundary, or mesoscale cold front, at its leading edge. This high pressure is caused by the cooling of the air from the evaporation of rainfall (commonly referred to as the cold pool). The meteorologist at the Hydrometeorological Prediction Center (HPC) analyzed this properly adding the mesoscale high.

http://avwxworkshops.com/forum/file.php?8,file=84,filename=18Z-Base-Reflectivity.gif

If he had looked at the 500 mb chart (below), he would have noticed that the primary air flow (shown by the red arrow) included a very broad trough in the western-third of the country. Whereas a ridge pattern covered most of the eastern two-thirds of the country. This "pattern" was generally stagnant, hence the reason for the stationary front. The "unusually long" front was separating the cooler air mass to the north with the warm and humid air mass to the south. It is not uncommon in this kind of weather regime defined by a ridge to see an MCS or two develop along the stationary front. These systems develop and "ride" along the flow as the flow pattern remains fixed - like a train on tracks.

http://avwxworkshops.com/forum/file.php?8,file=83,filename=13Z-500mb.gif

One of the products that Mac could have used even the night before his flight is Simulated Reflectivity. Simulated reflectivity is a model-based hourly forecast showing what the Nexrad image might look like in the future. It's not perfect, but often provides some of the best information for planning when convection is possible. The chart below is a 13 hour forecast valid at 13Z which clearly shows the MCS moving through the Ohio Valley in the morning.

http://avwxworkshops.com/forum/file.php?8,file=85,filename=13Z-Sim-Cut.gif

This product provides an hourly forecast. So it would have been easy to see where the convection was likely every hour from the time he woke up in the morning until the time he was ready to depart. Below is a 19 hour forecast valid at 19Z. Clearly shows where the convection was expected in the early afternoon which matches the Nexrad image above fairly well.

http://avwxworkshops.com/forum/file.php?8,file=86,filename=19Z-Sim-Cut.gif

There are plenty of other comments I could make about the remainder of his artcle, but he could have definitely made this an easy flight if he hadn't been so persistent about flying around the convection to the north. Based on the forecast and high pressure in the southeastern U.S. a route down the east coast across the Delmarva peninsula to cut across into North Carolina would have been very safe. Hindsight is 20/20 of course, but the forecasts were pretty clear and were supported by the "big picture" he ignored.]]> Scott Dennstaedt Scott's Aviation Weather Blog Fri, 23 Jul 2010 16:43:07 -0400 http://avwxworkshops.com/forum/read.php?2,220,220#msg-220 Ideas on improvement... (8 replies) http://avwxworkshops.com/forum/read.php?2,220,220#msg-220
There's no specific end-user product in mind here. There's a push by the AMS to learn what "users" of aviation weather information need to make the most informed decisions. This will apply to all stakeholders in aviation including forecasters, dispatchers, controllers, airport managers and pilots. The results (I'm not the only person writing a paper) may be used to improve or modify existing products or create new ones.]]> Scott Dennstaedt General Discussion Tue, 20 Jul 2010 22:14:05 -0400 http://avwxworkshops.com/forum/read.php?8,219,219#msg-219 Hole in this severe storm (no replies) http://avwxworkshops.com/forum/read.php?8,219,219#msg-219

http://avwxworkshops.com/forum/file.php?8,file=76,filename=Severe-Storm-With-Hole.jpg

]]> Scott Dennstaedt Scott's Aviation Weather Blog Tue, 06 Jul 2010 10:30:37 -0400 http://avwxworkshops.com/forum/read.php?8,218,218#msg-218 Cloud chart online B) (no replies) http://avwxworkshops.com/forum/read.php?8,218,218#msg-218 cloud types. Enjoy. :)-D]]> Scott Dennstaedt Scott's Aviation Weather Blog Tue, 06 Jul 2010 10:20:20 -0400 http://avwxworkshops.com/forum/read.php?8,216,216#msg-216 NWS may go mixed case for some of their text products! (no replies) http://avwxworkshops.com/forum/read.php?8,216,216#msg-216 public information statement. The current proposal to change from all caps to mixed case is mainly focused on public and plain language products for which formats are not fixed by national or international agreement. Domestic and international textual aviation products will not be affected unless or until such agreements are modified. So this will not apply to the area forecasts, AIRMETs/SIGMETs/convective SIGMETs, TAFs, etc. It may apply to severe thunderstorm watches and warning and tropical watches and warnings/statements that are sent to the public, but may not apply to convective outlooks and mesoscale discussions from the SPC that are meant to be forecaster to forecaster communication.

Attached is the Service Change Notice (SCN). Go to the bottom of this document and send an e-mail to the person listed if you have any comments relating to this change.]]> Scott Dennstaedt Scott's Aviation Weather Blog Wed, 30 Jun 2010 22:25:30 -0400 http://avwxworkshops.com/forum/read.php?8,214,214#msg-214 How about this FA? (no replies) http://avwxworkshops.com/forum/read.php?8,214,214#msg-214
000
FAUS43 KKCI 270145
FA3W
CHIC FA 270145
SYNOPSIS AND VFR CLDS/WX
SYNOPSIS VALID UNTIL 272000
CLDS/WX VALID UNTIL 271400...OTLK VALID 271400-272000
ND SD NE KS MN IA MO WI LM LS MI LH IL IN KY
.
SEE AIRMET SIERRA FOR IFR CONDS AND MTN OBSCN.
TS IMPLY SEV OR GTR TURB SEV ICE LLWS AND IFR CONDS.
NON MSL HGTS DENOTED BY AGL OR CIG.
.
SYNOPSIS...NO ROOM.
.
ND
W HLF...SCT050 BKN140 LYRD FL250. BKN CI. ISOL -TSRA. CB TOP
FL400. 04Z SCT150. OTLK...VFR.
E HLF...OVC100 LYRD FL300. NMRS -SHRA. SCT TSRA POSS SEV. CB TOP
ABV FL450. BECMG 0709 SCT-BKN080. OTLK...VFR.
.
SD
W HLF...BKN130 LYRD FL250. OVC CI. WDLY SCT TSRA POSS SEV. CB TOP
ABV FL450. BECMG 0406 SCT080-100. OTLK...VFR.
E HLF...SCT040 BKN080-100 LYRD FL300. WDLY SCT TSRA POSS SEV. CB
TOP ABV FL450. 08Z BKN070. SCT -SHRA. OTLK...VFR.
.
NE
PNHDL-SWRN...BKN140 TOP FL300. SCT -SHRA. WDLY SCT -TSRA. CB TOP
FL400. BECMG 0507 SCT-BKN CI. OTLK...VFR.
RMNDR...
N HLF...SCT-BKN050 BKN100 LYRD FL250. WDLY SCT -TSRA POSS SEV.
CB TOP FL450. BECMG 0709 BKN150. OTLK...VFR.
S HLF...SKC TO SCT CI. 04Z SCT050 SCT-BKN100 LYRD FL250. WDLY
SCT -TSRA POSS SEV. CB TOP FL450. OTLK...VFR.
.
KS
E HLF...SKC TO SCT CI. BECMG 0910 SCT130 SCT CI. WDLY SCT -TSRA.
CB TOP FL410. OTLK...VFR SHRA.
W HLF...SCT080-100 BKN150 LYRD FL250. BKN CI. WDLY SCT -SHRA/-
TSRA POSS SEV. CB TOP FL440. OTLK...VFR.
.
MN
NW...BKN050 LYRD FL250. SCT -SHRA. WDLY SCT -TSRA POSS SEV. CB
TOP FL430. OTLK...VFR.
NE...SCT030 SCT-BKN060 LYRD FL250. AFT 03Z SCT -SHRA. WDLY SCT -
TSRA. CB TOP FL400. 10Z OVC025. VIS 3-5SM -RA BR. OTLK...MVFR CIG
RA. 17Z VFR.
S HLF...SCT-BKN030 OVC070 TOP FL300. NMRS -SHRA. SCT TSRA POSS
SEV. CB TOP ABV FL450. 10Z BKN040. OCNL VIS 3-5SM -RA BR.
OTLK...VFR.
.
IA
NW...BKN035 OVC050 TOP FL300. SCT TSRA POSS SEV. CB TOP ABV
FL450. BECMG 0608 SCT025 SCT-BKN100. OTLK...VFR.
NE...BKN050-060 LYRD FL250. BECMG 0304 BKN040 LYRD FL300. SCT
TSRA POSS SEV. CB TOP ABV FL450. OTLK...VFR.
SW...SKC. BECMG 0406 SCT030 BKN050 LYRD FL250. SCT TSRA. TS POSS
SEV. CB TOP ABV FL450. 10Z OVC040. WDLY SCT -TSRA/-SHRA. CB TOP
FL430. OTLK...VFR.
SE...SCT-BKN CI. 08Z SCT040-050 OVC060-080 LYRD FL300. SCT TSRA.
TS POSS SEV. CB TOP ABV FL450. OTLK...VFR.
.
MO
XTRM NWRN...SKC. 08Z SCT050 SCT-BKN120 LYRD FL250. WDLY SCT -
TSRA. CB TOP FL400. OTLK...VFR.
RMNDR N HLF...SKC. 10Z SCT050 SCT100. WDLY SCT -TSRA/-SHRA. CB
TOP FL380. OTLK...VFR.
S HLF...SCT-BKN CI. OTLK...VFR.
.
WI
N HLF...SCT035 BKN150 LYRD FL250. BKN CI. BECMG 0305 BKN040
OVC100. SCT -TSRA. CB TOP FL380. AFT 08Z OVC025. OTLK...MVFR CIG
SHRA BR.
SW...BKN050 LYRD FL250. AFT 04Z SCT -TSRA/-SHRA. CB TOP FL380.
OTLK...VFR SHRA.
SE...BKN100 LYRD FL250. 05Z SCT040 BKN060. SCT -TSRA. CB TOP
FL410. OTLK...VFR SHRA.
.
LS UPR MI
W HLF...SCT010 SCT040 BKN100 LYRD FL250. 04Z BKN035 OVC080. SCT -
SHRA. WDLY SCT -TSRA. CB TOP FL400. AFT 09Z BKN010-015.
OTLK...MVFR CIG SHRA BR.
E HLF...SCT-BKN035 BKN150 LYRD FL250. 06Z SCT040 OVC130-150. AFT
BECMG 0910 OVC015. VIS 5SM IN SCT -SHRA. OTLK...IFR CIG SHRA.
.
LM LWR MI LH
W HLF..BECMG 0709 SCT060 BKN150 LYRD FL250. SCT -TSRA. CB TOP
FL440.OTLK...VFR SHRA.
NERN...BKN025 TOP 100. OCNL VIS 3-5SM -RA/BR. 07Z SCT010 BKN CI.
VIS 3-5SM BR. OTLK...VFR.
SERN...BKN040-050 LYRD FL250. SCT -SHRA. 04Z SCT025. OCNL VIS 3-
5SM BR. OTLK...VFR SHRA.
.
IL
N HLF...SCT-BKN060 BKN100 LYRD FL250. AFT 05Z SCT TSRA. TS POSS
SEV. CB TOP ABV FL450. OTLK...VFR SHRA.
S HLF...SKC TO SCT CI. AFT 08Z WDLY SCT -TSRA POSS..MAINLY NRN
PTNS. CB TOP FL450. OTLK...VFR.
.
IN
NRN 2/3...SCT040-050. ISOL -TSRA. CB TOP FL410. 03Z SKC. AFT 08Z
OCNL VIS 3-5SM BR. OTLK...VFR.
RMNDR...SCT050 BKN CI. WDLY SCT -TSRA. CB TOP FL440. 05Z SCT CI.
OCNL VIS 3-5SM BR. OTLK...VFR.
.
KY
E HLF...SKC. AFT 08Z OCNL VIS 3-5SM BR. OTLK...VFR.
W HLF...SCT040. ISOL -TSRA. CB TOP FL410. 04Z SKC. AFT 08Z OCNL
VIS 3-5SM BR. OTLK...VFR.
....

See the upcoming July 2010 e-Newsletter for the answer...it may surprise you!]]> Scott Dennstaedt Scott's Aviation Weather Blog Sun, 27 Jun 2010 12:14:11 -0400 http://avwxworkshops.com/forum/read.php?8,213,213#msg-213 Don't trust those SCITs! (no replies) http://avwxworkshops.com/forum/read.php?8,213,213#msg-213

http://avwxworkshops.com/etips/images/SCIT-1.gif

Now it is very unlikely that all of these SCITs are correct to determine the actual cell movement. But you don't know from looking strictly at this image. Just 10 minutes later, there are only two SCITs (they come and go sometimes) and there's still a 90-degree discrepancy.

http://avwxworkshops.com/etips/images/SCIT-2.gif

Discrepancies such as this often happen when a cell rapidly develops or is stationary. The algorithm sees "development" as movement. That is, the SCIT in the first diagram that is pointing to the left (west) likely was the result of a rapid increase in reflectivity (new growth) on the western side of the cell making it seem like the cell moved when, in fact, it was just getting bigger. It's not until the storm develops a bit more that you notice a distinct movement east as shown in the image loop below.

http://avwxworkshops.com/etips/images/SCIT-Loop.gif

]]> Scott Dennstaedt Scott's Aviation Weather Blog Fri, 25 Jun 2010 23:02:16 -0400 http://avwxworkshops.com/forum/read.php?8,212,212#msg-212 :( Trip Monitoring/Wx Briefs are now history... (no replies) http://avwxworkshops.com/forum/read.php?8,212,212#msg-212 Scott Dennstaedt Scott's Aviation Weather Blog Fri, 18 Jun 2010 20:34:51 -0400 http://avwxworkshops.com/forum/read.php?2,204,204#msg-204 "Valid Time" Question (1 reply) http://avwxworkshops.com/forum/read.php?2,204,204#msg-204
I hate advertising my ignorance on an Internet forum but here goes:

When a model forecast (e.g., HPC Day X 12-Hr PoP Fcst) is stamped with a "valid" time (e.g., 0000Z) is the prediction for the period before or after the valid time?

David]]> David Volkmann General Discussion Thu, 10 Jun 2010 09:42:16 -0400 http://avwxworkshops.com/forum/read.php?8,200,200#msg-200 Aviation climatology (no replies) http://avwxworkshops.com/forum/read.php?8,200,200#msg-200 neat site for the NWS eastern region of aviation climatology for wind, ceiling and visibility...just in case you were wondering.]]> Scott Dennstaedt Scott's Aviation Weather Blog Tue, 01 Jun 2010 21:11:00 -0400 http://avwxworkshops.com/forum/read.php?8,199,199#msg-199 Report severe weather on Twitter! (no replies) http://avwxworkshops.com/forum/read.php?8,199,199#msg-199 Twitter as a means to identify dangerous weather in progress. If you have a Twitter account, it is easy...just login to your account and prefix your Tweet with #wxreport and it'll will register a Tweet on your account as well as the NWS Twitter account. Just don't delete it...it'll go away in both places.]]> Scott Dennstaedt Scott's Aviation Weather Blog Mon, 31 May 2010 12:33:57 -0400 http://avwxworkshops.com/forum/read.php?8,198,198#msg-198 :X Most of what you will read about weather is worthless! (no replies) http://avwxworkshops.com/forum/read.php?8,198,198#msg-198
The thing that bothers me the most is that some of these pilots/instructors are highly respected and spout off "facts" or knowledge as if it were true. The sad part is that other pilots believe them without hesitation - they soak it up. They may use old wives' tales or rules of thumb that rarely are true when Mother Nature is at her worst. There are some very impressionable pilots out there listening.

Do yourself a huge favor. When you read something about weather written by a non-weather professional (even in a magazine), don't take it seriously. Here's one of my favorites. In February 2009, J. Mac McClellan wrote a pretty poor article about icing in Flying Magazine. He said in this article,

Quote:
In order for a drop of water to become supercooled and remain liquid it must be transported from air that is above freezing to cold air rather quickly.

Say what? I wonder where he got his weather training? A large percentage of icing clouds containing supercooled liquid water form in completely subfreezing environments where there isn't a hint of above-freezing air for hundreds of miles. His statement would imply that as long as the surface temperature is below freezing and the entire temperature profile aloft is below freezing, supercooled liquid water cannot exist. While we all wish that were the case during the winter months, it is far from the truth. You can read my response to his article here.

There are some aviation writers (such as Jack Williams) that are trained meteorologists and do provide some accurate information. While Bob Buck's book, Weather Flying, is fairly good, it still is written by a pilot who didn't have any formal weather training...and none of his book takes into consideration the many products we now enjoy on the Internet. When you read something written about weather ask yourself a simple question. Is this something I can apply on my next flight? Of course, I am speaking figuratively, but the best resources are those that teach you something you can immediately apply when the opportunity arises.]]> Scott Dennstaedt Scott's Aviation Weather Blog Fri, 28 May 2010 22:12:30 -0400 http://avwxworkshops.com/forum/read.php?2,179,179#msg-179 Synoptic chart (1 reply) http://avwxworkshops.com/forum/read.php?2,179,179#msg-179
Today I saw a synoptic chart from south Florida containing a marking I've never encountered before. It seems to be associated with a trough ahead of a cold front. I attach a pdf file of the synoptic chart. There is severe weather ahead of the cold front and I presume the marking on the synoptic chart is indicating this...

Tommy]]> Tommy Wiklind General Discussion Mon, 26 Apr 2010 20:50:36 -0400 http://avwxworkshops.com/forum/read.php?8,173,173#msg-173 Ceilings are always AGL (no replies) http://avwxworkshops.com/forum/read.php?8,173,173#msg-173
Area forecasts (FA) do report the height of cloud bases in MSL since it doesn't reference one particular airport. Although in some locations, the abbreviation CIG is used in the FA to denote a ceiling...in that case, it is AGL. But that's rare these days.]]> Scott Dennstaedt Scott's Aviation Weather Blog Sun, 18 Apr 2010 21:48:13 -0400 http://avwxworkshops.com/forum/read.php?8,171,171#msg-171 GOES-15 captures its first images of the Earth (no replies) http://avwxworkshops.com/forum/read.php?8,171,171#msg-171 more...]]> Scott Dennstaedt Scott's Aviation Weather Blog Thu, 08 Apr 2010 22:41:38 -0400 http://avwxworkshops.com/forum/read.php?8,169,169#msg-169 (tu) New help files being added (1 reply) http://avwxworkshops.com/forum/read.php?8,169,169#msg-169
Based on member feedback, I am in the process (given the time available) of creating help files for the guidance used in the Internet Wx Brief Roadmap. Keep in mind that you must be a Regular or Elite member of AvWxWorkshops.com to use the Roadmap.

You'll begin to notice a "help smiley" icon ?( posted next to a particular product or next to the title of a group of products as you can see to the right of the Surface Analysis title...

Clicking on this icon will take you to a workshop that provides a brief overview of the product(s) and how to use the guidance. It isn't meant to be comprehensive, however. These do take a while to create, so it may take a year or longer to create help for all products in the Roadmap. Moreover, this is in preparation for a new interactive tool that will make the Roadmap more useful providing features not available anywhere on the Internet. This will allow me to integrate the Roadmap with the training component of the website.

]]> Scott Dennstaedt Scott's Aviation Weather Blog Mon, 28 Jun 2010 16:48:12 -0400 http://avwxworkshops.com/forum/read.php?8,168,168#msg-168 (td) Flash and Java not supported on the iPad (1 reply) http://avwxworkshops.com/forum/read.php?8,168,168#msg-168
In some cases, however, Java tools like you will find on many of the weather sites encapsulated in the Internet Wx Brief Roadmap won't work either since Java isn't supported on the iPad. So if you purchase the iPad, don't expect to use it much on AvWxWorkshops.com. :X]]> Scott Dennstaedt Scott's Aviation Weather Blog Tue, 11 May 2010 20:20:34 -0400 http://avwxworkshops.com/forum/read.php?8,167,167#msg-167 (tu) The Rapid Update Cycle extended to 18 hours! (no replies) http://avwxworkshops.com/forum/read.php?8,167,167#msg-167 rucsoundings.noaa.gov]) are operational now out to 18 hours for the Op40 or Op20. Second, since the Forecast Icing Product (FIP) uses the RUC model there's a good chance that FIP might be extended as well, but it's not going to happen overnight. Based on my internal sources I think when they switch FIP over to WRF-RR in October (notice that I didn't include a year) they'll upgrade to an 18-hour forecast but not for now. It's actually fairly easy to do, but the issue is that it hasn't been verified out to those times, and therefore, the FAA doesn't want it out there just yet. Third, it'll greatly expand the domain to include Alaska, most of Canada and most of Mexico...esentially the domain used for the NAM.]]> Scott Dennstaedt Scott's Aviation Weather Blog Sat, 03 Apr 2010 21:34:35 -0400 http://avwxworkshops.com/forum/read.php?8,166,166#msg-166 :( No longer an IFR magazine contributing editor (no replies) http://avwxworkshops.com/forum/read.php?8,166,166#msg-166 50 articles written for IFR magazine under Paul Berge and Jeff Van West as editors. Given that I am now working a pseudo-full time day job (not aviation, weather or computer related), I don't have the time at the moment to keep the website going and consistently write. While you may see one or two articles from me a year, most of my writing now will be done for Twin & Turbine.

At this point I am not sure who will be writing weather-related articles, but since IFR flying and weather are inseparable, I hope they can find someone else to fill in for me.]]> Scott Dennstaedt Scott's Aviation Weather Blog Tue, 30 Mar 2010 17:16:52 -0400 http://avwxworkshops.com/forum/read.php?8,164,164#msg-164 :X Subtle change with AIRMETs on ADDS (1 reply) http://avwxworkshops.com/forum/read.php?8,164,164#msg-164 AIRMET charts on ADDS (like the one shown below) you will notice a lack of AIRMETs on these charts as of right now.

http://avwxworkshops.com/etips/images/Icing-AIRMETs.gif

At the moment, SIGMETs and convective SIGMETs now are the only en route advisory included where previously they did include AIRMETs as well as SIGMETs. What happened to the AIRMETs?

As I describe in this FREE e-Tip from January 2010, the G-AIRMET product has now graduated from the experimental stage and as of March 16, 2010, is now approved for operational use. A consequence of this (that I don't agree with) was to remove all of the AIRMETs from these static charts and force the pilot to look at the G-AIRMET display. What are G-AIRMETs you ask? Here is a FREE workshop that I created last year that explains the new G-AIRMETs if you are interested.

The problem is that there are many websites that reference these static AIRMET charts directly that will have the wrong label and will likely be captioned as, "AIRMETs and SIGMETs" which should just be labeled "SIGMETs" now...

Such as these sites...

[www.wrh.noaa.gov]
[www.wrh.noaa.gov]
[www.erh.noaa.gov]

...as well as dozens of other sites.

If you are looking for the original images, you can go to the Experimental ADDS website which still has the old charts available (at least for now). I also pulled in these Experimental ADDS charts now on the QWxik Brief. The standard AIRMETs also remain depicted on the AIR/SIGMETs Java Tool. Be careful looking at these static charts. I've already had a few e-mails from my members sounding quite confused and wondering why there are no adverse weather advisories depicted.]]> Scott Dennstaedt Scott's Aviation Weather Blog Mon, 22 Mar 2010 21:15:30 -0400 http://avwxworkshops.com/forum/read.php?8,163,163#msg-163 Estimating cloud height (no replies) http://avwxworkshops.com/forum/read.php?8,163,163#msg-163
A rule of thumb for estimating the lowest cloud base is based on the temperature and dewpoint at the surface. Find the dewpoint depression in degrees F and then double it. Add two zeros to the result.

For example, assume the temperature at the surface is 59°F and the dewpoint is 57°F. The dewpoint depression (temperature - dewpoint) is 2°F. Doubling this leads to a 4 and adding two zeros leads to an estimate for the cloud bases of 400 feet AGL.

Here is a METAR from Monroe, NC fairly close to my house. I noticed a low overcast ceiling in the morning so I decided to test this rule of thumb. The temperatures here are in degrees C, but converted 15.0°C = 59°F and 13.9°C = 57°F. This is the same calculation as above which estimated the cloud bases to be 400 feet. Turns out the ceiling was 500 feet. Not bad.

KEQY 121453Z AUTO 07004KT 6SM BR OVC00515/14 A2974 RMK AO2 SLP076 60001 T01500139 50003

The next hour (below), the temperature came up a bit while the dewpoint remained the same. This would lead to 60 - 57 = 3, multiplied by 2 to get 6 or 600 feet AGL. Still pretty close with a scattered layer at 700 feet.

KEQY 121553Z AUTO VRB05KT 10SM SCT007 OVC017 16/14 A2970 RMK AO2 SLP065 T01560139

and then the next hour (below) the temperature increased while the dewpoint again remained the same. This leads to 62 - 57 = 5, multiplied by 2 to get 10 or 1000 feet AGL. Now we're starting to diverge from reality.

KEQY 121653Z AUTO 10004KT 10SM FEW017 OVC024 17/14 A2970 RMK AO2 SLP062 T01670139

However, it goes without saying that as the dewpoint remained the same and the temperature increased, the ceilings did rise as expected. Watching the dewpoint depression trend at the surface can often hint at the trend in the ceiling as well. A dewpoint depression that is increasing means a general increase in the cloud height. If it is remaining the same, expect the cloud heights to trend the same. Lastly, if it is decreasing, expect the cloud heights to trend lower.]]> Scott Dennstaedt Scott's Aviation Weather Blog Fri, 12 Mar 2010 12:44:38 -0500 http://avwxworkshops.com/forum/read.php?8,158,158#msg-158 ASOS/AWOS locations (no replies) http://avwxworkshops.com/forum/read.php?8,158,158#msg-158 Google map that lists all of the AWOS/ASOS locations. This site provide you with the frequency as well as the phone number of each AWOS/ASOS in the system.]]> Scott Dennstaedt Scott's Aviation Weather Blog Mon, 22 Feb 2010 08:25:38 -0500 http://avwxworkshops.com/forum/read.php?8,157,157#msg-157 AIRMETs vs reality (no replies) http://avwxworkshops.com/forum/read.php?8,157,157#msg-157

Quote:
I'm a relatively new VFR pilot and fly purely for fun. Therefore, I'm extremely conservative with weather. This morning (2/14/10), I was planning to fly from KDNL to KMKS departing at 1700 UTC. VMC prevailed. VFR was forecasted for the route of flight. Radar showed no echoes. The sky was clear. Yet, an AIRMET ZULU was issued for the flight area.

WAUS42 KKCI 141445
MIAZ WA 141445
AIRMET ZULU UPDT 2 FOR ICE AND FRZLVL VALID UNTIL 142100
AIRMET ICE...NC SC GA OH WV VA
FROM FWA TO 20SSW APE TO 40SW EKN TO CLT TO 20WNW CHS TO 50N AMG
TO 50WNW PZD TO GQO TO HMV TO HNN TO CVG TO FWA
MOD ICE BLW 160. CONDS CONTG BYD 21Z THRU 03Z.

FRZLVL...RANGING FROM SFC-135 ACRS AREA
MULT FRZLVL 020-060 BOUNDED BY 40ESE AMG-100E CRG-50ENE OMN-
60S AMG-40ESE AMG
SFC ALG 20S VXV-20SE SPA-20SE CLT-60S RIC
040 ALG 30SSE LGC-30W MCN-30NW AMG-20NNW CRG-40E CRG-100E CRG-
200SSE ILM
080 ALG 160SE LEV-170ENE VRB-200ENE PBI
120 ALG 100WNW EYW-70ESE PBI

I canceled my flight (just in case.)

As I recall from my studies, visible moisture must be present for ice formation. As a VFR pilot, I cautiously avoid clouds. In absence of precipitation, how would this AIRMET have potentially affected my flight?

Visible moisture in subfreezing temperatures are required before ice can accrete on the airframe. In simple terms, that's referred to as structural icing. Induction icing is important, but it is not specifically forecast in an AIRMET. An AIRMET is a time-smeared forecast for widespread adverse weather conditions. Widespread is defined as an area covering more than 3,000 square miles (or about 60-percent the size of the state of Connecticut). Forecasters at the Aviation Weather Center (AWC) issue AIRMET Zulu for a widespread area of moderate icing. Whether or not visible moisture exists, if widespread icing is not expected to be of at least moderate intensity, they will not issue AIRMET Zulu for this area.

The other important consideration is that an AIRMET is a time-smeared forecast. That is, an AIRMET must cover a six hour period regardless if adverse weather will occur during the entire period. If the total AIRMET area to be affected during the six hour forecast period is large, it could be that only a small portion of this total area would be affected at any one time.

This was the case for the AIRMET text listed above. At 1445 UTC, the AWC issued AIRMET Zulu for an area that included northern Georgia, western North Carolina and western South Carolina. This AIRMET was valid through 2100 UTC.

http://avwxworkshops.com/forum/file.php?8,file=59,filename=AIRMET-No-Text.gif

Here's the planned route of flight from KDNL to KMKS at 1700 UTC.

http://avwxworkshops.com/forum/file.php?8,file=65,filename=DNL-MKS.gif

The area of icing was clearly expanding eastward with time. The G-AIRMET (below) is the best place to see this. Notice that I've included the first three G-AIRMET snapshops for icing valid at 15Z, 18Z and 21Z. You'll notice the area in northern Georgia, western North Carolina and western South Carolina is labeled as an area of icing from the surface (SFC) through 160 (16,000 feet). At 18Z, the area remains just about the same size, except it now only includes the area from 050 (5,000 feet) through 160 (16,000 feet). The last snapshot is valid at 21Z and you can see the eastern-most portion of the area expanded to cover most of the flight path from KDNL to KMKS again from 050 (5,000 feet) through 160 (16,000 feet).

http://avwxworkshops.com/forum/file.php?8,file=64,filename=G-AIRMETs.gif

This implies that an eastbound flight at 1700 UTC would not have encountered structural icing based these G-AIRMET snapshots. Additionally, at 1800 UTC, the icing was expected to be above 5,000 feet based on these G-AIRMETs.

There are several other products that could have helped make a safe decision to fly. AIRMETs are only one piece of guidance that has important limitations to understand which is not usually emphasized by most instructors. G-AIRMETs (described in this FREE workshop) are a way to better identify the hazard in both space and time. METARs, TAFs, PIREPs, Skew-T diagrams, satellite images and freezing level forecasts could have been used as well. It is the composite information that is important, not just one weather product.]]> Scott Dennstaedt Scott's Aviation Weather Blog Mon, 15 Feb 2010 10:35:20 -0500 http://avwxworkshops.com/forum/read.php?8,155,155#msg-155 NWS changes hail criteria for a severe storm (1 reply) http://avwxworkshops.com/forum/read.php?8,155,155#msg-155
Previously, the National Weather Service (NWS) issued Severe Thunderstorm Warnings whenever a thunderstorm is forecast to produce wind gusts to 58 miles per hour (50 knots) or greater and/or hail size 3/4 inch (penny-size) diameter or larger. For the past few years, offices that cover areas of Kansas have experimented using a warning criterion of one inch diameter hail. During the spring and early summer of 2009, this experiment expanded to other areas in the Central and Western U.S. Beginning January 5, 2010, the minimum size for severe hail nationwide increases to one inch (quarter-size) diameter. There will not be a change to the wind gust criterion of 58 mph.

This change is based on research indicating significant damage does not occur until hail size reaches 1 inch (quarter-size) in diameter, and as a response to requests by core partners in emergency management and the media. Particularly in areas of the Central U.S., the frequency of severe thunderstorm warnings issued for penny-size and nickel size hail might have desensitized the public to take protective action during a severe thunderstorm warning

In areas that experimented with changing to the one inch hail criterion, media partners stated their user feedback suggests warnings are now more meaningful. In addition, television networks receive fewer viewer complaints from breaking into programming for non-damaging storms. The Emergency Management community in those areas agreed that warnings carry more weight, and spotters now concentrate on the more significant events.]]> Scott Dennstaedt Scott's Aviation Weather Blog Sun, 04 Jul 2010 09:39:53 -0400 http://avwxworkshops.com/forum/read.php?2,154,154#msg-154 rap & ADDS exp sites (1 reply) http://avwxworkshops.com/forum/read.php?2,154,154#msg-154
weather.aero
rap.ucar.edu

... are down, and have been down for a bit.

What is the scoop?

* Orest]]> Orest Skrypuch General Discussion Sat, 13 Feb 2010 13:03:28 -0500 http://avwxworkshops.com/forum/read.php?8,151,151#msg-151 :X Why do pilots expect a miracle? (2 replies) http://avwxworkshops.com/forum/read.php?8,151,151#msg-151
What many pilots don't understand is that we're a loooooong way off from being able to consistently predict the weather even as much as 3 days out, much less 5 days. A forecaster could have looked at all of the available data with all of the available scientific understanding and still be WAY off in his/her forecast. Most of the forecasters that I know don't feel we should forecast specifics like temperatures, rain, snow, clouds, etc. more than 48 hours out. They feel we should just include a statement such as "temperatures will be above average" or "there is an above average chance of rain." However, the general public (pilots included) would be screaming for a more detailed forecast even if it turns out to be wrong.

All of us have had a common cold. When is the last time you went to your doctor and complained they were not able to cure that common cold? They are highly educated and should be able to do this, right? Unfortunately, the scientific understanding isn't there yet. In a similar way, forecasters don't have the scientific understanding (and data) to predict the weather consistently more than 48 hours in the future with any detail...especially the details the average pilot is looking for. Even then, a forecast 12 hours in the future can be a complete failure in some cases.]]> Scott Dennstaedt Scott's Aviation Weather Blog Thu, 04 Mar 2010 14:03:46 -0500 http://avwxworkshops.com/forum/read.php?8,150,150#msg-150 Review of the Cirrus Icing Awareness Course (no replies) http://avwxworkshops.com/forum/read.php?8,150,150#msg-150 Purpose of the program: The program is designed for pilots that have purchased a Cirrus SR22 that includes a certified TKS ice protection system (IPS). This course will satisfy the pilot training limitation in the Cirrus pilot operating handbook (POH). The POH requires that the pilot-in-command (PIC) must have successfully completed this course within the preceding 24 months prior to flight into forecast or known icing conditions.

Cost: The online course is priced at $69. Access to the online course expires 760 days after purchase.

To purchase: The online course can be purchased from the Cirrus Connection website here. Note that shipping charges will be applied to the purchase and eventually waived after the purchase since access to the course is only available online.

Scope: This online course contains a detailed description of the TKS IPS including its proper use and limitations. It also contains weather-related training as it relates to structural icing. This review will be strictly limited to the weather-related discussion included in this online course.

Note that in the discussion below, "they" will be used to reference the developer(s) of this course.

Course outline: The course contains seven modules as shown below.

http://avwxworkshops.com/forum/file.php?8,file=53,filename=Modules.gif

Additionally, it contains supplementary training materials below.

http://avwxworkshops.com/forum/file.php?8,file=54,filename=Supplementary-Materials.gif

Module 3 covers flight planning and will look at icing weather products in addition to some of the in-flight decisions that come with flight into known ice.

AIRMETs/SIGMETs: This module discusses the use of AIRMETs and SIGMETs as a way to describe general areas of icing. They do not explain, however, that an AIRMET is a time-smeared product valid over a six hour period. As such, if the total area to be affected during the forecast period is very large, it could be that only a small portion of this total area would be affected at any one time. AIRMET limitations are covered in this FREE e-Tip and this FREE Two Minute Video Tip.

Nothing is mentioned about new forecast guidance called the G-AIRMET. The G-AIRMET is a supplemental product that was released by the Aviation Weather Center in October 2008 and will become operational March 16, 2010. The G-AIRMET can identify the potential hazard much better spatially and temporally than the traditional AIRMET. The G-AIRMET product can be found on the Aviation Digital Data Service (ADDS) here with a workshop on how to use the product here.

Satellite images: This module briefly discusses the use of satellite imagery as it relates to snow cover and doesn't really delve into how they can be used for analyzing an icing environment. They caution that snow on the surface may appear to be clouds on the visible satellite image. It suggests to use the visible satellite loop to determine the presence of snow on the surface to distinguish it from clouds. That is, clouds in the loop generally change shape as they develop, move or dissipate, however, snow cover remains stationary. This is certainly excellent advice. However, this module fails to mention that ground fog and widespread low stratus also can occur. These clouds tend to have little or no movement on the visible satellite image loop either. It's ironic that the visible image they show in the course is one that contains upslope stratus in the central high plains.

This module also mentions that the infrared (IR) satellite image may help make this determination as well. This is true, however, there are several IR satellite images available. One of the best to determine snow cover is the Channel 2 - Channel 4 IR image that can be found here. Of all IR satellite images available it provides a much better contrast to make the snow versus cloud determination. The infrared image, especially one that is enhanced to show the cloud top temperature, is extremely valuable in analyzing the icing potential in clouds. However, this use of the IR image isn't covered in this module.

Freezing level charts: This is another excellent product to use to determine the presence or absence of structural icing. The product is only briefly mentioned and they fail to discuss the potential for multiple freezing levels. Often freezing rain and freezing drizzle are the result of two or more freezing levels as discussed in this training workshop.

Current Icing Product (CIP): This module discusses that CIP is one of the best products when determining the potential for structural icing conditions. While this is a great product to use, it does have some important limitations not discussed. CIP can miss a serious icing hazard from time to time as discussed in this training workshop. While it does mention the severity and supercooled large drop (SLD) icing product, nothing is mentioned that CIP is actually a suite of products to include CIP Probability as well. Masked CIP severity and the Forecast Icing Potential (FIP) are not discussed either.

Pilot reports (PIREPs): This module includes a very good discussion pertaining to the variability and subjectivity of icing PIREPs. They list the PIREP symbology for icing. However, they only show four of the eight possible symbols. Here is the complete list.

http://avwxworkshops.com/forum/file.php?8,file=55,filename=PIREP-Icing-Symbols.gif

It would have been useful to mention that PIREPs are used to determine the hourly CIP analysis. It also should have emphasized the importance of filing an icing PIREP and how to make an unambiguous pilot report of icing as discussed in this FREE workshop.

METARs and TAFs: This discussion provides very little preflight planning guidance from an icing perspective. The METAR discussion is focused strictly on using these surface observations to avoid an extended flight in icing conditions on arrival and departure. Instead, the discussion should have focused on using the observed precipitation type and sky cover. Precipitation type such as RA, DZ, TSRA, FZRA, FZDZ, ice pellets and unknown precipitation can be used to identify hazardous conditions aloft. All of these precipitation types may signal the potential for heavy icing including SLD. Also just as important, FZDZ may be occurring aloft and may not always be reported at the surface.

Sky cover is also important as well. Most icing occurs when the ceiling is reported as broken or overcast. Scattered clouds usually do not pose a significant hazard from an icing perspective.

The discussion of terminal forecasts (TAFs) focused completely on using them to select an appropriate alternate airport. The selection of an alternate destination is important, however, a description of precipitation type and sky cover would be in order. Also, TAFs can signal a deepening of the icing situation. Seeing a TAF go from BKN030 to OVC010 with time may signal deeper conditions, potentially increasing the icing threat for that airport.

In-flight weather: This discussion is very cursory. Nothing presented here other than an awareness that satellite-delivered weather can be useful while in flight. They suggest to upgrade to the Aviator Pro subscription to gain access to CIP and CIP SLD. While this might be useful as an overview of the icing condtions, the product only updates once an hour (about 15 to 20 minutes past the hour) and only provides data every three thousand feet. The product is already 20 minutes old (at best) by the time it gets to your receiver. Then the image on the multifunction display (MFD) remains the same for an additional hour, despite the fact that the icing conditions are changing in real time minute by minute.

Mountains: They suggest to avoid flying downwind of ridges or peaks because the air in this region may contain moisture that has been lifted quickly. There are lots of ways clouds form around mountains. Most of the time clouds form on the crest of the mountain. As the air moves over the ridge it will descend on the other side. Downward motion of the air causes the air to compress adiabatically which, in turn, increases the air's temperature and may lower its relative humidity to the point where clouds will tend to dissipate. Generally speaking, most of the serious icing occurs over the ridges and less downwind over the valleys. Here's what is mentioned in the Aviation Weather advisory circular AC 00-6A...

Quote:
Each mountainous region has preferred areas of icing depending upon the orientation of mountain ranges to the wind flow. The most dangerous icing takes place above the crests and to the windward side of the ridges. This zone usually extends about 5,000 feet above the tops of the mountains; but when clouds are cumuliform, the zone may extend much higher.

Later in Module 5, they do suggest to be aware of icing on the windward side of the mountains which tends to conflict with they provide in this module.

Module 4 is a scenario that follows a flight from Syracuse to Albany, NY. The difference between stratus and cumulus clouds is discussed as well as basic icing principles.

Temperature: They suggest that icing conditions can occur in the temperature range of +2°C to -40°C. It is not possible to accrete ice when the total temperature (skin surface temperature) is above 0°C. It is true that the theoretical lower limit is -40°C. At this temperature, supercooled liquid water cannot exist. However, icing is extremely rare below -35°C, especially outside of convective activity. See this e-Tip to read about the role of temperature in an icing environment.

Icing type: They suggest that glaze ice (clear ice) occurs at temperatures between +2°C to -5°C. Mixed ice occurs between -5°C to -15°C. Rime ice occurs between -5°C to -20°C. Unfortunately, there's no hard temperatures that can be identified. Factors of icing type include temperature, supercooled liquid water content (SLWC) and drop size. In other words, very small drops tend to produce rime icing even with temperatures only slightly supercooled, say -1°C to -4°C. Conversely, larger drops can produce clear icing even at highly supercooled temperatures, say -12°C to -15°C.

Mixed ice: Mixed icing generally occurs when the aircraft travels through a changing icing environment, normally this happens during a climb or descent. For example, an aircraft may climb through a cloud with the temperature in the cloud bases around -4°C. Given the smaller cloud drops that are typically found in the bases, the aircraft may begin to accrete rime icing. As the aircraft climbs through the cloud into colder conditions near the tops the temperature drops to -13°C. Given the same drop size, the aircraft would continue to accrete rime icing at these colder temperatures. However, if the drops became substantially larger as is typically seen near the tops, the icing type might change from rime to clear. Essentially, the icing is classified as mixed due to the change in the icing environment as the aircraft climbed through the icing conditions.

Glaze (clear) ice: They indicate that clear icing is the most hazardous form of icing because it forms at warmer temperatures and can contain more moisture. It is true that clear icing presents a significant icing hazard, but not because the atmosphere can contain more moisture necessarily. Clear icing is problematic because it is usually a function of drop size as well as temperature. Larger drops are more likely to penetrate the boundary layer of all of the aircraft surfaces (not just the leading edges) and freeze. The freezing is slower and the drops that strike the leading edges don't freeze on contact and run back toward the aft of the surface (flaps and ailerons, for example). The warmer the static temperature, the greater the possibility of clear ice.

Icing in stratus clouds: They say, "Ice in stratus clouds can differ dramatically. Severe ice can be encountered only a few thousand feet above a layer where only a trace will accumulate." I'm assuming this means that you can climb through a layer that starts out as trace near the bases and changes to severe near the tops. If so, that's an accurate statement, but it doesn't always have to happen that way.

Later they state that a change of 3,000 feet is usually enough to get away from a band of icing. This is generally true of stratiform clouds, but not cumuliform clouds. The thickness of the stratiform cloud layer is a function of (in)stability, lift and to some degree temperature. The thickness of clouds has a tendency to decrease with decreasing temperature. Below -25°C stratiform clouds were found to form thin layers having a depth usually no more than 300 feet. While a stratiform cloud deck can be as thick as 14,000 feet, the overall average and median depth of supercooled stratiform cloud layers are 2,200 feet and 1,600 feet, respectively.

Even in rather deep synopitic situation such as a warm front, the icing tends to be vertically banded in multiple layers. There may even be cloud-free regions where icing may be absent. These are hard to predict with any certainty, but changing altitudes may allow you to find an altitude with relatively little structural icing.

As they suggest, it is true that changing altitudes versus staying at the same altitude is a better choice. However, flight at the MEA might only allow a climb. Typically, a climb will expose the aircraft to icing at or near the tops of the cloud which usually contain a higher liquid water content and larger drops.

Supercooled Large Drops: This discussion identifies the processes that produce SLD and was fairly good. Although they did describe the classical freezing rain (FZRA) process, they did not use the terms freezing rain (FZRA) and freezing drizzle (FZDZ). They also did not mention the non-classical freezing rain process which occurs 92% of the time. SLD is described in more detail in this e-Tip.

Module 5 is a scenario that follows a flight from follows a long cross-country from Washington to Ohio. Icing considerations when flying through mountains and warm fronts are introduced as well as other important meteorological information.

Static air temperature: The narrator makes a mistake by referring (twice) to the static air temperature as the "saturated" air temperature. This can be confusing to a pilot and something that should have been caught prior the release of the online course.

Total air temperature: They introduce the total air temperature (skin surface temperature) as being directly related to the speed of the aircraft. This adiabatic heating they reference is also called "ram-air rise." They did not give any specifics about how much of a temperature rise you can reasonably expect. More importantly, they did not emphasize that the rise in the total temperature is only related to the immediate leading edges and the ram-air effect quickly diminishes to zero just a few centimeters from the immediate leading edge. A Cirrus pilot should reasonably expect a ram-air rise of two or three degrees Celsius on the immediate leading edges, but this does not mean that a rise will occur over the entire airframe.

Mountains: They discuss how mountains will allow air to lift to the point of condensation. Specifically they discuss mountains in the Pacific Northwest containing a lot of moisture including the potential for SLD. This is true. The Cascades do contain a high chance of large drops primarily because it tends to be a clean environment with few cloud condensation nuclei. Cleaner environments tend to produce fewer, but larger drops including SLD.

Snow: They mention snow falling throughout a couple of slides in this module. They don't point out that snow falling from the clouds typically lessens the icing threat (and intensity) in the clouds especially near the bases. Keep in mind that snow doesn't mean the lack of supercooled liquid water. In fact, snow falling can be a mixed phase cloud consisting of mostly ice crystals, but also liquid water. At very cold temperatures (surface temperatures below -15°C), snow falling from a cloud likely means the cloud is glaciated as long as a temperature inversion does not exist aloft.

Module 6 is a scenario that will follow a flight through a spring-time cold front resulting in a severe ice encounter.

Occluded fronts: They suggest that an occluded front is the result of a cold front "catching up to" a warm front. Actually there are two types of occluded fronts - what's called a cold occlusion and a warm occlusion. Occluded fronts occur when the frontal cyclone (low pressure area) reaches a mature state.

A cold occlusion is the one they describe and occurs when the air behind the occluded front is colder than the air ahead of it. The cold occlusion acts in a similar way to a cold front in that the the cold air behind the front undercuts the cool air ahead of it.

http://avwxworkshops.com/forum/file.php?8,file=56,filename=Cold-Occlusion.jpg

A warm occlusion is less common and occurs when the air behind the occluded front is warmer than the air ahead of it. The warm occlusion acts in a similar way to a warm front in that the cool air behind the front is lighter than the cold air ahead of the front. This causes the cool air to pass over the top of the cold air.

http://avwxworkshops.com/forum/file.php?8,file=57,filename=Warm-Occlusion.jpg

From an icing perspective, each type of occlusion will impact the icing that may or may not be present.

Freezing rain: This scenario outlines a flight through a cold front with cumuliform clouds. After the aircraft enters the clouds the flight starts to encounter freezing rain. This is certainly not a very likely event. Freezing rain is typically a very shallow event experienced near the surface (typically within the first two or three thousand feet) as described in this training workshop. This is accompanied by a temperature inversion. With cumuliform clouds along a cold front, the temperature profile is unstable and a significant inversion aloft is not likely. However, SLD is very likely in this kind of environment. Supercooled cloud drops are typically greater than 40 microns and can be near 70 or 80 microns in some cumuliform clouds.

Final thoughts: Overall I liked the use of the simulated Cirrus SR22 throughout most of the presentation. Pictures of actual ice accumulation on the unprotected surfaces was indeed enlightening, but more images along with the background/history of the icing environment would have been very helpful.

The flight planning modules contained very little preflight weather planning techniques as it relates to icing. This leaves the pilot with only a few tidbits of knowledge on how to properly characterize an icing environment. All of the scenarios involved short-term planning; nothing was mentioned about how characterize the icing environment 24 to 48 hours in advance.

The summary of this course ends with the following statement, "While we cannot hope to teach you all there is to know about flight into known icing conditions, this course should serve as a starting point in you icing education." This is one of the most pertinent statements in the course and basically sums up my thoughts. While there is a fair amount of weather education presented on icing in this course, it is a far cry from complete or thorough. A pilot that has very little knowledge of structural icing and has never planned a flight through known icing conditions will not be prepared to do so even after taking this course.

Flight into known icing conditions can be done safely, but you must respect the amount of analysis time that is required to determine how to minimize your exposure to structural icing.]]> Scott Dennstaedt Scott's Aviation Weather Blog Thu, 17 Dec 2009 08:30:14 -0500