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As a temporary fix, we are now providing "Bak40" soundings when "Op40" soundings are requested. "Bak40" soundings are soundings generated from the 40km output grid from the backup RUC model, which we are continuing to run here at GSD. (These same soundings are provided when "Bak40" soundings are requested directly.)

We believe we will have a much better solution, which will provide soundings from the operational RAP, within a few days.

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Scott Dennstaedt
Also this will mean that the Op40 or Op20 selection on the RUC soundings Java tool is no longer available. For the time being you can use the Bak20 or Bak40 as the input data source or you can use the RR1h data source for soundings from the new model.

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The Aviation Weather Center (AWC) is conducting a research project on low level turbulence away from the influences of terrain and in the presence of stronger wind. The AWC is requesting pilots, controllers, and dispatchers make an extra effort to provide PIREPs below 12,000 feet during the nighttime hours--primarily from 0200 UTC through 1100 UTC. This includes reports of negative turbulence as well. The focus of this project runs across the central plains; from Texas to Canada, between the Rockies and the Ohio River Valley, but any nighttime PIREP is greatly appreciated. The project runs through September 1, 2012.

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The National Transportation Safety Board determines the probable cause(s) of this accident as follows. The pilot's loss of control of the airplane during an instrument approach in turbulent weather conditions.

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At 1001, the airplane began a series of right turns consistent with a holding pattern around the OMGEY intersection that lasted until approximately 1021. At approximately 1028 the airplane descended to about 5,200 feet and began tracking toward the PADOH intersection, with the flaps configured to the 50-percent position. At this time the autopilot was engaged in altitude hold vertical mode and global positioning system lateral mode with approach coupled. Over the next 1.5 minutes, the airspeed gradually decreased from around 115 knots to around 80 knots, while the normalized angle of attack increased from around 0.075 to around 0.800.

At 1029:24, the autopilot disengaged while the airplane was flying at an indicated airspeed of 76 knots and a normalized angle of attack of 0.811. Five seconds later, the stall warning briefly activated, at an indicated airspeed of 86 knots and a normalized angle of attack of 0.814. Over the next 17 seconds the airplane rolled 46 degrees left wing down, followed by 42 degrees right wing down. The airplane then rolled left while simultaneously pitching to 25 degrees nose up before the stall warning again activated continuously for 13 seconds. While the stall warning was active, the airspeed decreased from 79 knots to 64 knots, before increasing again to 88 knots, and the normalized angle of attack increased from 0.768 to 0.998, before decreasing again to 0.695 one second after the stall warning deactivated. The pitch then began to decrease to 86 degrees nose down while the reaching a maximum bank of 153 degrees left wing down at 1030:12. During this time the indicated airspeed reduced from 79 knots to 64 knots, before increasing again as the airplane continued to pitch nose down. The airplane then began to pitch up toward a level attitude, while the airspeed increased from 88 knots to 171 knots over a period of 8 seconds. During the descent, the airplane reached a vertical speed of -12,000 fpm and the normal acceleration (g-force) increased to 3.29 g's. The CAPS handle was activated at 1030:21, while the airplane's attitude was 2 degrees left wing down, the pitch was 2 degrees airplane nose up, and the airspeed was 171 knots. The CAPS rocket deployed one second later, at an altitude of 4,000 feet msl (about 1,200 feet agl). The recorded data ended at 1031:26.

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The National Weather Service (NWS) Boston Area Forecast described a warm front extending over the region, with the forecast for West Virginia indicating overcast clouds at 3,000 feet msl with cloud tops to 30,000 feet, visibility 4 miles in moderate rain and mist; with a slight improvement in ceiling and visibility by 1400. Marginal visual meteorological conditions (MVMC) were expected to continue through the evening.

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The forecast was amended by AIRMET Sierra for IMC over the area.

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The NWS had AIRMETs Sierra and Tango current over the region for IMC, mountain obscuration conditions, and moderate turbulence below 15,000 feet. The conditions were expected to continue through 1700.

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Further east, over Maryland and Virginia, an AIRMET for low-level wind shear and strong surface winds was in effect, as well as a Convective SIGMET for an area of embedded severe thunderstorms, a weather watch for the potential for severe tornadic thunderstorms, as well as a SIGMET for high altitude turbulence.

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The closest terminal area forecast to the to the accident site was from Elkins-Randolph County Airport (EKN), Elkins, West Virginia, located about 34 nautical miles west of W99. The forecast prior to the flight’s departure expected MVMC to IMC to prevail due to light to moderate rain and mist, with broken to overcast ceilings.

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The NWS Surface Analysis Chart for 1100 depicted the accident site ahead, or west, of a warm front associated with a deepening low pressure system over the Virginia and North Carolina boarder (sic) south of the accident site.

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Clouds and precipitation were predominating over the region, with severe thunderstorms over the Atlantic coastal states and extensive IMC over West Virginia, Pennsylvania, Maryland, and Virginia.

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The NWS hourly Radar Summary Chart for 0919 depicted an extensive area of weather echoes over the area, with a few areas embedded intense to extreme intensity precipitation echoes in the vicinity of West Virginia. The NWS Sterling, Virginia (LWX) WSR-88D base reflectivity images surrounding the period of the accident depicted an area of echoes of 25 to 35 dBZ “light to moderate” intensity echoes over KW99 and the accident site.

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The 0800 upper air sounding for Washington/Dulles International Airport (IAD), Sterling, Virginia, located about 70 nautical miles east of the accident site, depicted a saturated environment from the surface to approximately 18,000 feet msl. A defined frontal inversion was noted from the surface to about 1,300 feet msl, with light surface winds below the inversion and a rapid veering of the wind to the south and increase in wind speed with height.

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There was an urgent pilot report from a pilot operating a Cirrus SR22 at 0944 in the vicinity of Elkins, West Virginia, or approximately 25 miles northeast of the W99, reporting severe turbulence at 8,000 feet.

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The 1042 weather observation at W99, included calm winds, 3 statute miles visibility in heavy rain, an overcast ceiling at 800 feet, temperature 16 degrees C, dew point 13 degrees C, and an altimeter setting of 29.61 inches of mercury. The remarks section indicated an hourly precipitation of 0.25 inches and there were no remarks indicating that thunderstorms or lightning were present.

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The pilot continued to hold for approximately 30 minutes while he waited for the weather to improve, and reported that there was virtually no turbulence until he entered the hold. He was cleared by air traffic control to initiate the approach, and noted that the winds at his altitude were gusting out of the southeast around 40 knots.

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The Rapid Refresh (RAP) model will be implemented May 1st. The RAP will be used as the forecast model that provides the initial forecast conditions instead of the Rapid Update Cycle (RUC) for Automated Icing CIP, FIP and Turbulence GTG products. In conjunction with the upgrade of RAP model, GTG will be upgraded from 20KM to 13KM resolution. During the upgrade process some interruptions of data availability may be possible. Further guidance can be found in the TIN for the RAP and GTG TIN.

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The new scheduled date for RAP implementation is now either 1 May or 8 May 2012. It was found that due to a script problem in the NCO version, the RAP had not been assimilating radar reflectivity data in 2012. Two other smaller issues were found also due to script issues: lack of GOES cloud-top data over full RAP domain, and issuing of 0h/analysis fields after the RAP digital filter initialization instead of before. The NCEP Centers will re-evaluate the RAP guidance now including these revisions for the next 30 days. Again, the planned implementation date is now set for 1 May or 8 May (both Tuesdays).

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Due to the computing needs of some coming operational implementations, this run likely will become less timely, and will have more missed cycles. Starting 3/20/12, the number of missed cycles will increase SIGNIFICANTLY.

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From tragedy we draw knowledge to improve the safety of us all.

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Although the RAP evaluation resulted last Monday in a recommendation at NCEP for implementation, some computer issues have arisen since then resulting in a delay in the RAP implementation until no earlier than Tuesday, 3 April 2012. As the new implementation date is hardened, that information will be posted.