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ADDS METARs Java tool:
Depicting thunderstorms 
Automation
can be wonderful at times. But it also might not be
telling the complete story. Such is the case with
the METARs Java tool from the Aviation
Digital Data Service (ADDS).
The METARs Java tool depicts the
surface observations (METARs) in a graphical form similar to the
example on the right. Hovering your cursor over this station
model will cause the full METAR (coded) text to instantly
appear on the display. While the graphical form of the METAR
is very useful, always remember that is does not depict all of
information contained in the textual version especially when
thunderstorms are occurring in the terminal area or its vicinity.
But first, let's review a few
definitions. The U.S. terminal area is defined as the
cylindrical volume of airspace within a 5 statute mile radius from the
center of the airport's runway complex. The terminal area's
vicinity is the donut-shaped cylindrical region with radii of 5 and 10
statute miles from the center of the airport's runway complex.
Note that the terminal area's vicinity excludes the
terminal area (the area within 5 statute miles).
When a
thunderstorm is currently observed within the terminal area, the METAR
will include
TS such as the example above
for Lansing, Michigan (KLAN).
In this
case, the ADDS graphical display will show one of the three possible
thunderstorm symbols to
the left of the station's sky cover and flight category symbol (center
circle/square). Note that the precipitation type and
intensity is not displayed, however. Consequently, a single thunderstorm
symbol such as this represents several possible precipitation types and
intensities (if any) to include light rain (-TSRA), moderate rain
(TSRA), light snow (-TSSN), moderate snow (TSSN), light ice pellets
(-TSPL) or
moderate ice pellets (TSPL).
When heavy precipitation and a
thunderstorm is being observed in the terminal area, the thunderstorm
symbol changes slightly as shown above
Pontiac, Michigan (KPTK).
Do not let the single dot above the thunderstorm symbol fool
you. This symbol is used to represent heavy rain (+TSRA),
heavy snow (+TSSN) or
heavy ice pellets (+TSPL).
When a
thunderstorm is observed to be within the vicinity of the terminal area
it is encoded in the METAR as VCTS. There may or may not
be precipitation
falling within the terminal at the time of the report. A
thunderstorm in the vicinity is depicted graphically with half of the
thunderstorm symbol as it is above
for Sarnia Airport (CYZR)
in Ontario, Canada. Note that while moderate rain is being
reported at the airport based on the text of the METAR, the display
does not depict the precipitation type or intensity
graphically.
Lastly, if thunderstorms are reported
in the airport's vicinity (VCTS) and
the precipitation being observed in the terminal area is heavy (rain,
snow or ice pellets), the half-thunderstorm symbol is omitted and only
the precipitation type is shown as it is above for
Somerville, New Jersey (KSMQ).
Heavy rain (+RA) is depicted as four dots on the ADDS
graphical display to the left of the station's sky cover and flight
category symbol.
It is important never to rely solely on
the graphical display. It does not completely depict the
textual METAR and may leave out important details. Moreover, the
remarks section of the METAR will often contain valuable information as
well.
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