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Southeast Discussion

By: NWS
By: NWS

A WEAK SFC LOW (IN THE 1010-1012 MB RANGE CONTINUES TO MUDDLE ITS WAY TO THE E-SE OFF THE LA COASTLINE THIS EVENING...AND WHILE ITS SHIELD OF PRECIP LOOKED QUITE IMPRESSIVE EARLIER IN THE DAY (EVEN AS OF LATE THIS AFTERNOON)...THE AREA AS A WHOLE HAS BEGUN TO DIMINISH IN INTENSITY AND COVERAGE AS THE LOW MAKES ITS TREK INTO THE VERY DRY AIR WHICH IS STILL ENTRENCHED OVER OVER CWA. IT WAS THIS DRY AIR WHICH INITIALLY GAVE US THE THOUGHT OF AT LEAST SOME POTENTIAL FROZEN PRECIP ACROSS PARTS OF THE REGION...BUT COMPARING REALITY TO THE 18 UTC GFS (OF WHICH MODEL HAS BEEN THE MOST BULLISH FOR SNOW OR MIXED PRECIP POTENTIAL) ALREADY SHOWS SOME MAJOR DISCREPANCIES...ESPECIALLY IN CRITICAL SOUNDINGS TO DETERMINE PARTIAL THICKNESS LAYERS. THE 18 UTC GFS HAD A FCST 00 UTC TAE SOUNDING TONIGHT WITH A SFC TEMP OF 40 DEGREES F (ALBEIT WITH A STRONG INVERSION TO 1000 MB OF NEAR 50 DEGREES)...BUT IN REALITY ...THE ACTUAL SFC PARCEL AT THE 23 UTC RELEASE TIME WAS IN THE MID 50S...WITH ONLY A GRADUAL COOLING THEREAFTER. IN FACT...ONE HAS TO GO ALL THE WAY UP TO 800 MB TO REACH THE FREEZING POINT...AND ALTHOUGH THERE IS "SOME" DRY AIR TO "WET BULB" DOWN SHOULD PRECIP BEGIN FALLING...THIS LAYER IS NOT NEARLY AS IMPRESSIVE AS THE EVENT OF A COUPLE OF WEEKS AGO...WHERE SOME MIXED PRECIP DID FALL IN TALLAHASSEE AND SIGNIFICANT ACCUMULATING SNOW DID OCCUR FURTHER TO THE N AND W. ALSO...ANOTHER CRITICAL SIGN WHICH IS POINTING AGAINST ANY FROZEN PRECIP IS THE 24 HR VERTICAL TEMPERATURE TREND...WHICH THE 00 UTC TAE SOUNDING SHOWS A WHOPPING 5 DEGREE CELSIUS (OR 9 DEGREE F) RISE FROM 875 MB ALL THE WAY DOWN TO THE SFC. THIS RISE WAS NOT ACCURATELY DEPICTED IN THE 18 UTC GFS FCST SOUNDING AS WELL...SO SEE ALMOST NO REASON WHATSOEVER TO RE-INTRODUCE ANY FROZEN PRECIP INTO OUR GRIDS. ALSO...BASED ON THE LATEST 18 UTC GUIDANCE (MAV...GRIDDED MOS...AND CONFIDENCE GRIDS) IN CONJUNCTION WITH THE RADAR AND SFC ANALYSES...BELIEVE THAT THE CURRENT FCST POPS ARE WELL ON TRACK AS IS...SO NO UPDATES OF THAT SORT ARE PLANNED AT THIS TIME. ALSO...THANKS TO MOB FOR THE COORD. ON THE LACK OF FROZEN PRECIP POTENTIAL. PERHAPS THE MOST INTERESTING ASPECT OF TONIGHT`S FCST WILL BE THE LIKELY "MIDNIGHT TO 2 AM EST" LOW TEMPS WHICH COULD VERY WELL DROP A FEW DEGREES BELOW FREEZING BEFORE THE CLOUDS ARRIVE (ESPECIALLY ALONG THE SUWANNEE RIVER VALLEY WHERE CTY HAS ALREADY DIPPED TO 36 AS OF 02 UTC...SO MAY LOWER TEMPS WELL TO THE EAST A FEW MORE DEGREES FROM JEFFERSON COUNTY EASTWARD IN THE FL BIG BEND. OVER THE COASTAL WATERS...WINDS ARE STILL VERY LIGHT AND QUITE VARIABLE AHEAD OF THE SFC LOW...BUT SHOULD STILL PICK UP MORE SIGNIFICANTLY OUT OF THE NE LATE TONIGHT AND TOWARDS DAYBREAK.


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