Short Term Discussion

By: NWS
By: NWS

SUBTLE TIMING DIFFERENCES EXIST BETWEEN THE GFS/NAM/LOCALWRF. HOWEVER...THESE DIFFERENCES HAVE NOW NARROWED TO A COUPLE HOURS OR LESS. LINEAR EXTRAPOLATION OF THE SQUALL LINE TYPE FEATURE ACROSS LOUISIANA SHOWS A TIMING CLOSER TO THE GFS/WRF...SO WILL RELY MORE ON THOSE MODELS FOR THIS FORECAST CYCLE. AS THE STORM SYSTEM MOVES EAST ACROSS THE NORTHERN GULF COAST...THE AIRMASS WILL CONTINUE TO MOISTEN...THOUGH DESTABILIZATION WILL BE VERY SLOW TO OCCUR. THE QUALITY OF THE AIRMASS ACROSS THE NORTH IS NOT ALL THAT GOOD. DEWPOINTS ARE IN THE MID 60S AT THE BUOYS...WITH COASTAL DEWPOINTS BARELY REACHING 60 IN THE LOUISIANA DELTA REGION. THIS IS LARGELY DUE TO THE LOW LEVEL FLOW BECOMING SO BACKED ACROSS THE GULF COAST THAT THE TRAJECTORIES ARE ESSENTIALLY PARALLEL TO THE COASTLINE. THERE IS A NARROW CORRIDOR OF SOUTHEASTERLY/SOUTHERLY FLOW JUST AHEAD OF THE COLD FRONT RESPONSIBLE FOR DEWPOINTS REACHING THE LOW TO MID 60S. GIVEN THIS SET UP SEVERAL OTHER TIMES EARLIER THIS SEASON...THE PROSPECTS FOR STRONG TO SEVERE STORMS TO MAKE IT INTO OUR FORECAST AREA IS QUITE LOW. IN FACT...THE MODELS ARE DOING A VERY GOOD JOB OF SHOWING THE LINE ENCOUNTERING THIS INCREASINGLY STABLE AIRMASS ACROSS OUR REGION AND WEAKENING WITH TIME. WIND SHEAR (AS IS USUALLY THE CASE) IS SUFFICIENT FOR ROTATING UPDRAFTS /0-6 KM 50 TO 60 KNOTS/. SIMULATED REFLECTIVITY DATA IN THE 29/09Z WRF IS SHOWING TWO SUPERCELLULAR STRUCTURES WELL SOUTH OF THE REGION OVER THE GULF OF MEXICO MOVING TOWARD THE GULF COAST JUST BEFORE DAYBREAK. AS THESE STRUCTURES NEAR THE COAST...THEY TAKE ON AN INCREASINGLY ELEVATED APPEARANCE. THUS...FEEL THE OVERALL SEVERE POTENTIAL OVER THE LAND AREAS IS LOW...AND WILL ONLY INCLUDE MENTION OF GUSTY WINDS OVERNIGHT. WITH THE MODELS VERY CLOSE IN THEIR TIMING...WILL GO AHEAD AND INCREASE POPS TO 100 PERCENT IN THE WESTERN COUNTIES AND TAPER DOWN TO THE EAST. FOR SATURDAY...WILL SHOW POPS TAPERING DOWN QUICKLY THROUGHOUT THE MORNING AND AFTERNOON HOURS AS THE SYSTEM MOVES BY. IT LOOKS LIKE IT WILL INDEED BY DRY IN TALLAHASSEE BY 10 AM ET...JUST IN TIME FOR WEATHERFEST...OUR BIG OUTREACH EVENT OF THE YEAR. IN FACT...THE SUN WILL LIKELY POP OUT BY MIDDAY HELPING TO CREATE A MUCH WARMER EVENT THAN LAST YEAR. AS INSTABILITY WILL BE LIMITED...DON`T EXPECT MUCH IN THE WAY OF THUNDERSTORMS AFTER ABOUT 15Z. SATURDAY NIGHT...THE AIRMASS BEHIND THIS SYSTEM IS NOT SIGNIFICANTLY COLD. MUCH OF THE COLD AIR WILL BE VECTORED MORE INTO THE TENNESSEE VALLEY...SO DON`T EXPECT TEMPERATURES TO DROP MUCH (IF AT ALL) BELOW FREEZING ON SUNDAY MORNING. SUNDAY AND MONDAY...MOSTLY CLEAR SKIES WITH DIMINISHING COOL ADVECTION WILL CREATE A BREEZY AND COOL DAY ON SUNDAY WITH TEMPERATURES ONLY IN THE MID TO UPPER 50S. THE RIDGE OF HIGH PRESSURE WILL SETTLE OVER NORTHEAST TENNESSEE ON SUNDAY EVENING AND THIS WILL KEEP WINDS ELEVATED ENOUGH TO ALLOW TEMPERATURES TO DROP BELOW FREEZING OVER MUCH OF THE AREA ON MONDAY MORNING.


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