Prolonged Freezing Rain over OK
Posted by JAC on 1/28/2010, 2:35 pm
 MESOSCALE DISCUSSION 0074 NWS STORM PREDICTION CENTER NORMAN OK 1218 PM CST THU JAN 28 2010 AREAS AFFECTED...CENTRAL...SRN...NERN AND N-CENTRAL OK INTO EXTREME NWRN AR CONCERNING...WINTER MIXED PRECIPITATION VALID 281818Z - 282215Z A PROLONGED PERIOD OF FREEZING RAIN IS EXPECTED TO OCCUR ACROSS MUCH OF CENTRAL OK THIS AFTERNOON...WHILE ALSO SPREADING TOWARD E-CENTRAL/NERN OK AND EXTREME NWRN AR BY LATE AFTERNOON/EARLY EVENING. ACROSS N-CENTRAL OK...DRY LOW LEVEL AIR WILL EVENTUALLY MOISTEN WITH TIME...LEADING TO SLEET TRANSITIONING TO SNOW TOWARD 00Z. FARTHER S OVER S-CENTRAL OK...DRY AIR MAY ADVECT INTO THE AREA DURING THE AFTERNOON...CAUSING THE WET BULB ZERO LINE TO SHIFT SOUTH TOWARD THE RED RIVER...WHICH WOULD INCREASE THE PROBABILITY FOR SIGNIFICANT FREEZING RAIN. AT 17Z...SFCOA DATA INDICATED THE WET BULB ZERO LINE EXTENDED FROM ROUGHLY FSM/W-CENTRAL AR TO A LOCATION IMMEDIATELY S OF FSI IN SWRN/S-CENTRAL OK. SURFACE OBSERVATIONS SUGGEST THAT NELY WINDS ACROSS MUCH OF OK WILL CONTINUE TO USHER IN DRY LOW LEVEL AIR TOWARD S-CENTRAL OK...WHICH WOULD FAVOR A SWD PUSH OF THE WET BULB ZERO LINE TOWARD THE RED RIVER. MEANWHILE...SIGNIFICANT WARM AIR ABOVE THE SURFACE CONTINUES TO BE DRAWN INTO THE LOW LEVEL CYCLONIC CIRCULATION ATTENDANT TO THE SWRN CONUS UPPER TROUGH...WITH A PROMINENT WARM NOSE /5-6 DEG C/ CENTERED NEAR 850 MB PER 15Z OUN SPECIAL SOUNDING. AS THE SHIELD OF PRECIPITATION ASSOCIATED WITH THE WARM CONVEYOR BELT CONTINUES TO SPREAD NWD INTO OK...MODEL FORECAST SOUNDINGS INDICATE THERMODYNAMIC PROFILES WILL REMAIN FAVORABLE FOR FREEZING RAIN ACROSS MUCH OF CENTRAL OK...PERHAPS SPREADING SWD TOWARD THE RED RIVER GIVEN THE RECENT TRENDS IN SURFACE OBSERVATIONS. FORECAST SOUNDINGS ALSO SHOW LAPSE RATES STEEPENING TOWARD 00Z OVER S-CENTRAL/CENTRAL OK...WITH A FEW HUNDRED J/KG OF MUCAPE ROOTED NEAR 700 MB SUGGESTIVE OF CONVECTIVELY ENHANCED PRECIPITATION RATES. OTHERWISE...AS THE 40-50 KT S-SELY LLJ BEGINS TO SHIFT EWD WITH THE EMERGING UPPER TROUGH TOWARD EVENING...HEAVIER PRECIPITATION RATES WILL BEGINS TO SPREAD ACROSS E-CENTRAL/NERN OK INTO EXTREME NWRN AR...AT WHICH POINT MODEL GUIDANCE DEPICTS RAPID WET BULB COOLING AND MOISTENING IN THE BOUNDARY LAYER...RESULTING IN THE ONSET OF FREEZING PRECIPITATION PERHAPS MIXED WITH SLEET. FARTHER W FROM CENTRAL INTO N-CENTRAL OK...FREEZING RAIN MAY TRANSITION TO SLEET MORE QUICKLY DUE TO COOLER 850 MB TEMPERATURES...WITH SNOW BECOMING MORE PROBABLE TOWARD 00Z PER SREF GUIDANCE. ..GARNER.. 01/28/2010 |
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