MD 0181 CONCERNING WINTER MIXED PRECIPITATION FOR FREEZING RAIN AND SLEET
MESOSCALE DISCUSSION 0181
NWS STORM PREDICTION CENTER NORMAN OK
0232 AM CST THU FEB 21 2013
AREAS AFFECTED...FREEZING RAIN AND SLEET
CONCERNING...WINTER MIXED PRECIPITATION
VALID 210832Z - 211430Z
SUMMARY...FREEZING RAIN RATES WILL INCREASE FROM SW-NE THROUGH THE
MORNING...WITH 0.10-0.25 INCH ICE ACCUMULATIONS POSSIBLE ON ELEVATED
SURFACES ACROSS NE OK/NW AR. PRIMARILY SLEET IS EXPECTED FROM SE KS
INTO PARTS OF SW MO WHERE THE BOUNDARY LAYER IS COLDER/DEEPER AND
THE WARM NOSE ALOFT IS LESS PRONOUNCED.
DISCUSSION...A SWATH OF PRECIPITATION IS EXPANDING OVER WRN/NRN OK
IN A ZONE OF STRONG LOW-LEVEL WAA/FRONTOGENESIS...AS WELL AS
DIFFERENTIAL CVA IN ADVANCE OF A STRONG SHORTWAVE TROUGH EJECTING
ENEWD FROM NM. THE OOZ SOUNDING FROM OUN SHOWED THE DEVELOPING WARM
NOSE NEAR 800 MB...AND THIS WARMING ABOVE THE SURFACE WILL CONTINUE
TO SPREAD NEWD WITH TIME. MEANWHILE...A SHALLOW BOUNDARY LAYER WITH
TEMPERATURES NEAR FREEZING HAS BEEN MAINTAINED ACROSS NE OK...NRN
AR...AND SW MO BY AN INFLUX OF CONTINENTAL AIR FROM THE SURFACE
RIDGE ACROSS THE OH VALLEY. AS PRECIPITATION RATES INCREASE THROUGH
THE MORNING...WET BULB COOLING WILL HELP MAINTAIN THE NEAR-FREEZING
BOUNDARY LAYER...AND THE RISK FOR ACCUMULATING FREEZING RAIN.
THOUGH HOURLY RAINFALL RATES COULD EXCEED 0.25 INCHES PER HOUR WITH
ELEVATED CONVECTION...THE SOMEWHAT MARGINAL SURFACE TEMPERATURES
SUGGEST THAT SOME OF THE RAINFALL WILL GO INTO RUNOFF PRIOR TO BEING
ABLE TO FREEZE. THUS...WHILE ICE ACCUMULATIONS COULD APPROACH 0.25
INCHES ON VEGETATION AND ELEVATED/EXPOSED SURFACES...THE RISK FOR
POWER OUTAGES AND MORE SERIOUS ICE ACCUMULATIONS ACROSS NE OK AND NW
AR WILL BE LIMITED BY THE MARGINAL TEMPERATURES. SOMEWHAT GREATER
ICE ACCUMULATIONS WILL BE POSSIBLE ALONG THE TRANSITION ZONE FROM
FREEZING RAIN TO SLEET ACROSS EXTREME SE KS/SW MO.
FARTHER N INTO SE KS AND SW MO...THE BOUNDARY LAYER WILL REMAIN
COLDER/DEEPER WITH A LESS-PRONOUNCED WARM NOSE ALOFT...AS SAMPLED BY
THE 06Z SPECIAL SOUNDING FROM SGF. THIS WILL FAVOR SLEET AS THE
PREDOMINANT PRECIPITATION TYPE...AND THERE WILL BE THE POTENTIAL FOR
A COUPLE OF INCHES OF SLEET ACCUMULATION GIVEN THE EXPECTED
PRECIPITATION RATES.
..THOMPSON.. 02/21/2013
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...LZK...SGF...EAX...TSA...TOP...ICT...OUN...
LAT...LON 38619441 38149346 37519265 36879232 36029215 35469225
35039255 34929324 35289433 35719541 35899701 36179766
36529777 37009730 37609643 38039526 38409462 38619441
via SPC Forecast Products http://www.spc.noaa.gov/products/md/md0181.html
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