MESOSCALE DISCUSSION 0175
   NWS STORM PREDICTION CENTER NORMAN OK
   0709 AM CST WED FEB 20 2013
   
   AREAS AFFECTED...CENTRAL OK
   
   CONCERNING...HEAVY SNOW 
   
   VALID 201309Z - 201715Z
   
   SUMMARY...SNOWFALL RATES OF ONE INCH PER HOUR LOCALLY WILL AFFECT
   PARTS OF THE CENTRAL OK VICINITY THIS MORNING.
   
   DISCUSSION...DESPITE WET-BULB TEMPERATURES WHICH WERE WELL ABOVE
   FREEZING EARLIER THIS MORNING ACROSS CENTRAL OK...MELTING ALOFT OF
   PERSISTENTLY FALLING PRECIPITATION ACROSS THIS AREA HAS COOLED THE
   LOWER-TROPOSPHERIC COLUMN WITH TIME.  THIS COOLING HAS NOW REACHED
   THE SURFACE...WITH TEMPERATURES PER THE OK MESONET HAVING FALLEN
   SEVERAL DEGREES OVER THE PAST 1-2 HOURS DOWN TO NEAR FREEZING.  THIS
   MELTING-INDUCED COOLING HAS RESULTED IN A CHANGEOVER FROM RAIN TO
   SNOW IN MANY AREAS PER LATEST SURFACE OBS.  WHILE THE PRECIPITATION
   REMAINS FAIRLY HEAVY/STEADY...PERSISTENT MELTING-INDUCED COOLING
   WILL MAINTAIN A THERMAL STRUCTURE SUPPORTIVE OF CONTINUED SNOWFALL. 
   WITH WIDESPREAD PRECIPITATION STILL EVIDENT ON RADAR OVER NWRN
   TX/SWRN OK WHICH WILL SHIFT NEWD WITH TIME...EXPECT THIS
   MELTING/COOLING PROCESS TO CONTINUE DESPITE BACKGROUND WARM
   ADVECTION -- WHICH WILL THUS SUPPORT SNOWFALL FOR AT LEAST A FEW
   HOURS.  EVENTUALLY...AS PRECIPITATION SLACKENS LATER THIS MORNING
   AND THE MELTING-INDUCED COOLING LESSENS...THE LOWER TROPOSPHERE WILL
   WARM A FEW DEGREES AND SNOWFALL SHOULD REVERT BACK TO RAIN. 
   MEANWHILE...SEVERAL INCHES OF WET SNOW COULD ACCUMULATE IN MANY
   AREAS -- AT LEAST ON GRASSY SURFACES.
   
   ..GOSS.. 02/20/2013
   
   
   ATTN...WFO...TSA...OUN...
   
   LAT...LON   36189703 35569627 34789609 34569691 34839817 35569879
               36469825 36189703