MESO: Mesoscale Discussion 2208

ACUS11 KWNS 251532
SWOMCD
SPC MCD 251531
TXZ000-OKZ000-252030-

MESOSCALE DISCUSSION 2208
NWS STORM PREDICTION CENTER NORMAN OK
0931 AM CST TUE DEC 25 2012

AREAS AFFECTED...CNTRL/SWRN/S-CNTRL OK...WRN NORTH TX AND PARTS OF
N-CNTRL TX

CONCERNING...WINTER MIXED PRECIPITATION

VALID 251531Z - 252030Z

SUMMARY...INITIALLY MIXED PRECIPITATION DEVELOPING OVER...AND 120
STATUTE MILES EITHER SIDE OF THE RED RIVER...WILL INCREASE IN
COVERAGE AND INTENSITY DURING THE NEXT HOUR OR TWO. PRECIPITATION
WILL TRANSITION TO ALL SNOW BETWEEN 17Z AND 21Z.

DISCUSSION...WATER VAPOR LOOPS DEPICTS A WELL-DEFINED CYCLONIC SWIRL
MARKING THE CENTER OF A COMPACT MID-LEVEL VORT MAX 55 NNW ABI AS OF
1445Z...WHICH IS TRACKING EWD. PRECIPITATION RATES WILL LIKELY
INCREASE DURING THE NEXT HOUR OR TWO...OWING TO STRONG DCVA
PRECEDING THE CYCLONE CENTER...COMBINED WITH ISENTROPIC ASCENT ATOP
AN OROGRAPHICALLY ENHANCED COLD DOME E OF THE ROCKIES. WITH
LOW-LEVEL TRAJECTORIES EMBEDDED WITHIN A WARM CONVEYOR BELT FAVORING
THE INFLUX OF RELATIVELY RICHER MOISTURE -- UPSTREAM SOUNDINGS AT
00Z AND 12Z SUGGESTING LOWEST 100-MB MEAN MIXING RATIOS OF
4-7 G/KG -- PRECIPITATION RATES WILL FURTHER INCREASE AS THE FORCING
FOR ASCENT INCREASES.

THROUGH 17Z...A MIX OF PRECIPITATION WILL OCCUR OWING TO THE
EXISTENCE OF WARMER AIR ALOFT -- E.G. ELEVATED WARM NOSE SAMPLED BY
THE 12Z NORMAN SOUNDING FEATURING 2-2.8C TEMPERATURES IN THE
900-815-MB LAYER. SLEET...ALONG WITH FREEZING RAIN WITH RATES OF
0.05-0.10 IN PER HOUR...WILL BE POSSIBLE...ESPECIALLY ACROSS S-CNTRL
OK IN CLOSER PROXIMITY TO WARMER TEMPERATURES ALOFT. RAIN WILL
REMAIN POSSIBLE ACROSS PARTS OF N-CNTRL TX WHERE ABOVE-FREEZING
TEMPERATURES EXIST THROUGH A DEEPER LAYER IN THE LOWER TROPOSPHERE.
PRECIPITATION WILL MORE QUICKLY TRANSITION TO SNOW WITHIN AN ARC
FROM CNTRL OK TO SWRN OK AND WRN NORTH TX...AS DEEPER COLD AIR WRAPS
AROUND THE NWRN QUADRANT OF A ERN-TX SFC LOW AND ADIABATIC COOLING
OCCURS WITH FORCING FOR ASCENT LEADING THE MID-LEVEL VORT MAX.

BETWEEN 17Z AND 21Z...SNOW WILL BECOME WIDESPREAD...WITH THE
PRECIPITATION-TYPE TRANSITION ZONE SHIFTING EWD/SEWD ACROSS S-CNTRL
OK AND NRN TX. SNOWFALL RATES REACHING 1-1.5 IN/HR WILL OCCUR AS
MID-LEVEL ASCENT EXTENDS THROUGH THE DENDRITIC GROWTH ZONE CENTERED
AROUND 600 MB. THE HEAVIEST SNOWFALL RATES WILL OCCUR ACROSS
SWRN/S-CNTRL OK AND WRN N TX...WHERE CONFLUENCE WITHIN A DEFORMATION
ZONE ALOFT SHOULD LOCALLY ENHANCE THE ASCENDING BRANCH OF A
FRONTOGENETIC CIRCULATION W/NW OF THE DEEPER CYCLONE.

OF NOTE...LOCALIZED BLIZZARD CONDITIONS WILL BE POSSIBLE ACROSS
SWRN/S-CNTRL OK AND ADJACENT NRN TX...WHERE FORECAST SOUNDINGS
INDICATE 0-1-KM MEAN FLOW INCREASING TO 30-40 KT. OK MESONET
OBSERVATIONS ALREADY INDICATE 20-30 MPH SUSTAINED NLY WINDS WITH
HIGHER GUSTS ONGOING. WIND SPEEDS SHOULD INCREASE OWING TO THE
TIGHTENING SFC PRESSURE GRADIENT AND INCREASING DIFFERENTIAL COLD
ADVECTION IN THE LOW LEVELS SUPPORTING DESTABILIZATION JUST ABOVE
THE SFC. FREQUENT GUSTS OF 35-40 MPH MAY OCCUR IN SOME
LOCATIONS...SUPPORTING WHITEOUT CONDITIONS/NEAR-ZERO VISIBILITIES.

..COHEN.. 12/25/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...FWD...OUN...SJT...

LAT...LON 33849692 32889699 32519731 32369789 32749902 34089948
34859959 35359924 35709871 35669777 35259734 33849692

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