morning Discussion NWS Tallahassee, Fla.
Posted by chucky7777 on 9/23/2010, 2:56 pm
.......NWS Forecast discussion......LONG TERM (SATURDAY NIGHT THROUGH THURSDAY)
ALL THE 00 UTC GLOBAL GUIDANCE FORECAST A LARGE CUTOFF 500 MB LOW TO
DEVELOP OVER MUCH OF THE EASTERN U.S. LATE THIS WEEKEND THROUGH
EARLY NEXT WEEK. THE DIFFERENCE IS IN THE DETAILS. THE GFS AND ITS
ENSEMBLE MEAN FORECAST THIS LOW FARTHER SOUTH (OVER THE GULF COAST
STATES) AND TAKE THIS LOW SLOWLY WESTWARD THROUGH THURSDAY. THE
ECMWF AND GEM HAVE THE LOW CENTERED FARTHER NORTH...AND NOT QUITE AS
CUT OFF FROM THE MAIN WESTERLIES (NO RETROGRADING). THUS THE
GFS/ENSEMBLE MEAN KEEP OUR AREA IN THE WARM SECTOR LONGER...AHEAD OF
A COMPLEX FRONTAL SYSTEM. THE ECMWF/GEM BRING A COLD FRONT THROUGH
OUR REGION BY MID WEEK. THE GFS/ENSEMBLE MEAN ALSO FORECAST A LARGE
TROPICAL CYCLONE (YET TO DEVELOP) TO MOVE INTO NORTH FL BY MID TO
LATE NEXT WEEK...WHICH WOULD RESULT IN A WET AND WINDY WEATHER EVENT
FOR US. WHILE THE ECMWF/GEM ALSO DEVELOP A LARGE TROPICAL CYCLONE IN
THE WESTERN CARIBBEAN EARLY NEXT WEEK...THEIR SOLUTION (WITH THE 500
MB TROUGH AND SURFACE FRONTAL SYSTEM FARTHER EAST) SHEARS THE
CYCLONE OUT SOUTH AND EAST OF OUR FORECAST AREA. WITH THIS MID
LATITUDE WEATHER SO FAR SOUTH (INCLUDING A BAROCLINIC
ZONE...VERTICAL WIND SHEAR...AND VERY DRY AIR ALOFT)...IT SEEMS
UNLIKELY THAT THE GFS SOLUTION OF AN INCREASINGLY-TROPICAL CYCLONE
WILL VERIFY (AS THE GFS FORECAST CYCLONE PHASE DIAGRAM FROM FSU
INDICATES). WE WOULD EXPECT THE SYSTEM TO BECOME LESS WARM CORE AND
SYMMETRICAL AS IT MOVES NORTHWARD. THE GFS ENSEMBLE MEMBER SPREAD IS
ABOUT AS LARGE AS IT GETS...INDICATING A LOT OF UNCERTAINTY WITH
THIS FORECAST. WE OPTED TO GO WITH THE 12 UTC WEDNESDAY ECMWF/GEM
SOLUTION...BRINGING THE COLD FRONT SLOWLY THROUGH OUR REGION BY
EARLY TO MID WEEK...BUT KEEPING A NORTH-SOUTH ORIENTED MOISTURE BAND
OVER OUR EASTERNMOST ZONES (WHERE THERE WILL REMAIN A SLIGHT CHANCE
OF RAIN). WE EXPECT MORE CHANGES WILL HAVE TO BE MADE TO THIS
FORECAST WITH EACH MODEL CYCLE...AS SMALL CHANGES IN TIMING AND
POSITIONING OF THIS FRONT WILL LIKELY HAVE LARGE IMPACTS ON OUR
VARIOUS FORECAST PARAMETERS. IN FACT...EVEN THOUGH THE 00 UTC ECMWF
WAS SIMILAR TO ITS PREVIOUS RUN (WHICH WE USED FOR THIS FORECAST
PACKAGE)...THERE ARE ALREADY SIGNIFICANT DIFFERENCES IN OUR
WIND/DEWPOINT/POP FORECAST. THIS IS AN UNUSUALLY LOW CONFIDENCE
FORECAST.

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Looks good to go! - canetrakker, 9/23/2010, 1:52 pm
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