Long Term Discussion

By: NWS
By: NWS

LONG TERM (SUNDAY THROUGH THURSDAY)...THERE ARE STILL SIGNIFICANT
MODEL DIFFERENCES IN THE EXTENDED PERIOD. THE MODELS BEGIN THE
PERIOD IN AGREEMENT WITH A LARGE 500MB TROF CARVING ITS WAY ACROSS
THE NATIONS MID SECTION. AFTER SUNDAY THE MODELS BEGIN TO DIVERGE
WITH THE ECMWF AND GEM FORECASTING THE INITIAL TROF TO BE ABSORBED
INTO THE LONGWAVE FLOW AND RACE OFF TO THE NORTHEAST. BEHIND THIS
TROF...BOTH MODELS FORECAST ANOTHER SHORTWAVE DIVING OUT OF THE
PLAINS TOWARDS THE SOUTHEASTERN U.S. HERE THE GEM AND ECMWF DIVERGE
WITH THE EURO FORMING A CUTOFF LOW THAT MEANDERS OVER THE CENTRAL
GULF COAST STATES THROUGH THE END OF THE PERIOD. THE GEM IS MORE
PROGRESSIVE WITH THE SHORTWAVE AND DOES NOT DEVELOP A CUTOFF LOW.
THE GFS PROVIDES A MUCH DIFFERENT LOOK AT THE EXTENDED PERIOD. IT
BRINGS THE INITIAL TROF SLOWLY SOUTHEASTWARD TO A POSITION OVER THE
NORTHERN CENTRAL GULF STATES BEFORE RETREATING SLOWLY
NORTHEAST...BEING ABSORBED IN THE MAIN FLOW OFF THE EXTREME
NORTHEASTERN U.S. COASTLINE BY THURSDAY. THUS...NO SECONDARY
SHORTWAVE AND NO CUTOFF LOW. THESE DIFFERENCES ARE CRITICAL AS ALL
OF THE GUIDANCE BRINGS SOME FORM OF NEWLY FORMED TD FIFTEEN NORTH TO
A POSITION JUST SOUTH OF CUBA BY THURSDAY. I SAY SOME FORM OF TD
FIFTEEN BECAUSE IT APPEARS THE MODELS ARE SUGGESTING A SECONDARY LOW
FORMING ON THE BACKSIDE OF TD FIFTEEN ON TUESDAY. WITH SO MUCH
UNCERTAINTY IN THE EXTENDED IT IS HARD TO CHOOSE FROM THE GUIDANCE
WITH ANY CONFIDENCE. THUS...THE MAIN CONCERN WILL BE THE POSITIONING
OF THE UPPER TROF AND ITS FUTURE INTERACTIONS WITH ANY TROPICAL
FEATURE ENTERING THE GULF. WILL WAIT FOR A LITTLE MORE AGREEMENT
BETWEEN THE SUITE OF GUIDANCE BEFORE MAKING A CONFIDENT FORECAST.


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