MESOSCALE DISCUSSION 0178
NWS STORM PREDICTION CENTER NORMAN OK
0357 PM CST SAT FEB 28 2009
AREAS AFFECTED...NERN AR...WRN TN...NRN MS...FAR NWRN AL
CONCERNING...WINTER MIXED PRECIPITATION
VALID 282157Z - 010200Z
SNOWFALL/SUBFREEZING TEMPERATURES ARE SLOWLY SPREADING INTO NRN
MS...AND A RECENT CHANGE OVER TO SNOW HAS BEEN OBSERVED IN TN NEAR
MEMPHIS. WHILE MDT/HVY SNOWFALL MAY BRIEFLY BE POSSIBLE AT
TIMES...THE MAIN CONCERN LIES WITH THE SLOW NATURE OF THE SYSTEM AND
POTENTIALLY ANOMALOUS OVERALL SNOW TOTALS FOR THE REGION.
A VIGOROUS UPPER LOW IS NOW CENTERED ROUGHLY NEAR THE KS/MO/OK/AR
BORDERS. AT THE SURFACE...ARCTIC HIGH PRESSURE CONTINUES TO BUILD
SWD THROUGH THE CNTRL STATES...WHILE AN INVERTED TROUGH AXIS HAS
STRENGTHENED...EXTENDING WNWWD THROUGH NRN AL/MS...NWWD THROUGH THE
TN/AR BORDERS...AND NWD INTO WRN MO. THIS HAS REMAINED A FAVORED
AREA FOR PRECIPITATION DEVELOPMENT IN CONJUNCTION WITH STRONG UPPER
DIVERGENCE/FAVORABLE JET DYNAMICS AS A 95+ KT 500 MB JET...OBSERVED
ON RECENT PROFILER DATA...NOSES INTO THE AREA. COLD AIR ADVECTION
HAS SEEMINGLY BEEN FASTER THAN MOST MODELS HAVE PREVIOUSLY
INDICATED...AND RECENT OBSERVATIONS INDICATE MODERATE SNOW IS
ONGOING...WHILE ACARS SOUNDINGS SHOW PROFILES ARE NOW SUBFREEZING.
ADDITIONALLY...TRAFFIC/WEBCAMS ACROSS NRN MS ARE INDICATIVE THAT A
TRANSITION TO SNOW HAS OCCURRED AS WELL...AND ACCUMULATION HAS
ALREADY BEGUN. INITIAL RATES...PERHAPS LACKING UNDER A MID LEVEL DRY
SLOT...WILL IMPROVE OVER TIME AS THE UPPER LOW SLOWLY MOVES SEWD.
MOISTURE SEEN ON WV AND RADAR IMAGERY WILL THEN WRAP
AROUND...PROVIDING ADDITIONAL SUPPORT FOR SNOW AS TEMPERATURES
CONTINUE TO COOL ACROSS THE SOUTHEAST. ENSEMBLE AND DETERMINISTIC
MODELS SEEM TO INDICATE GREATER ACCUMULATIONS WILL OCCUR AFTER 00Z
INTO THE OVERNIGHT TIME FRAME...WITH THE POSSIBILITY OF ANOMALOUS
TOTALS OWING TO THE INITIAL/RELATIVE SLOW MOVEMENT OF THE UPPER LOW.
..HURLBUT.. 02/28/2009
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