Mesoscale Discussion 2211

Issued

Dec 25, 2012, 12:11 PM CST (18:11 UTC)

Expired

Dec 25, 2012, 5:15 PM CST

In force

5 hr

Issued by

the Storm Prediction Center

The Western Arkansas radar (KSRX), 56 km from the middle of the area, began a volume at 18:10 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

968 
ACUS11 KWNS 251811
SWOMCD
SPC MCD 251811 
ARZ000-OKZ000-TXZ000-252315-

MESOSCALE DISCUSSION 2211
NWS STORM PREDICTION CENTER NORMAN OK
1211 PM CST TUE DEC 25 2012

AREAS AFFECTED...S-CNTRL/SERN/E-CNTRL OK...W-CNTRL/CNTRL/N-CNTRL AR

CONCERNING...WINTER MIXED PRECIPITATION 

VALID 251811Z - 252315Z

SUMMARY...MIXED PRECIPITATION WILL OCCUR FROM S-CNTRL OK EWD/ENEWD
INTO CNTRL/N-CNTRL AR...WITH A PHASE CHANGE TO SNOW OCCURRING FROM W
TO E THIS AFTERNOON INTO THE EVENING.

DISCUSSION...RECENT WATER VAPOR IMAGERY DEPICTS A MID-LEVEL VORT MAX
BECOMING INCREASINGLY SHEARED ACROSS N-CNTRL TX. THE LEADING WARM
CONVEYOR BELT EXHIBITS A SHARP BACK EDGE INVOF THE SABINE RIVER AT
THE INTERFACE OF AN IMPINGING DRY CONVEYOR BELT. STRONG WAA WITHIN
THE WARM CONVEYOR BELT WILL CONTINUE TO YIELD AN INCREASE IN
PRECIPITATION RATES DURING THE NEXT SEVERAL HOURS...WHILE
PRECIPITATION IS MAINTAINED ON THE BACKSIDE OF A CORRESPONDING SFC
CYCLONE AS WELL.

...THROUGH 21Z...
ACROSS CNTRL AR...FORECAST SOUNDINGS DEPICT 4-6C TEMPERATURES WITHIN
AN ELEVATED WARM LAYER BETWEEN 900 AND 850 MB...WITH THE LITTLE ROCK
12Z RAOB HAVING SAMPLED 6-7C TEMPERATURES IN THAT LAYER. MELTING
PROCESSES/LATENT COOLING AND INCREASING FORCING FOR ASCENT HAVE
LIKELY CONTRIBUTED TO SOME COOLING ALOFT...THOUGH THE WARM LAYER
WILL LIKELY STILL BE SUFFICIENT FOR HYDROMETEOR MELTING. AND...WITH
MANY SFC OBSERVATIONS INDICATING WET-BULB ZERO TEMPERATURES BELOW
0C...FREEZING RAIN WITH RATES OF 0.05-0.10 IN/HR MAY EVOLVE.

FARTHER TO THE N/W ACROSS N-CNTRL AR INTO PARTS OF E-CNTRL
OK...COOLER TEMPERATURE PROFILES ALOFT WILL SUPPORT ONLY PARTIAL
MELTING OF HYDROMETEORS ATOP SUBFREEZING WET-BULB ZERO SFC
TEMPERATURES...YIELDING SLEET/SNOW. SNOWFALL RATES OF 1-1.5 IN/HR
MAY ENSUE WITHIN BANDS OF HEAVIER PRECIPITATION...OWING TO STRONG
MESOSCALE ASCENT ACCOMPANYING FRONTOGENETIC CIRCULATIONS.

ACROSS S-CNTRL/SERN OK...WARMER LOW-LEVEL PROFILES ARE INITIALLY
SUPPORTING RAIN...THOUGH THE INTRUSION OF A DEEPER LAYER OF COLD AIR
WILL SUPPORT A TRANSITION TO SLEET/SNOW FROM W TO E. SNOWFALL RATES
OF 1-1.5 IN/HR WILL BE POSSIBLE...AS STRONG DCVA PRECEDING THE VORT
MAX CROSSES THE AREA.

...AFTER 21Z...
PRECIPITATION WILL PROGRESSIVELY TRANSITION TO SNOW FROM W TO E AS
DEEPER COLD AIR ENTERS THE AREA...WHILE WRAPPING AROUND THE DEEP
CYCLONE. SNOWFALL RATES OF 1-1.5 IN/HR WILL REMAIN POSSIBLE INTO THE
EVENING...AS ASCENT IS MAINTAINED IN ASSOCIATION WITH CONFLUENT FLOW
ON THE BACKSIDE OF THE CORRESPONDING 700-MB CYCLONE.

..COHEN.. 12/25/2012

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

ATTN...WFO...LZK...SHV...TSA...FWD...OUN...

LAT...LON   35399524 36029298 35759177 35189158 34719181 34089318
            33889456 33839605 34029672 34679667 35399524

Mesoscale Discussions in Arkansas, 2012Mesoscale Discussions in Oklahoma, 2012Every mesoscale discussion in 2012

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.