SWOMCD
SPC MCD 142347
ILZ000-MOZ000-IAZ000-ARZ000-OKZ000-KSZ000-150345-
MESOSCALE DISCUSSION 2470
NWS STORM PREDICTION CENTER NORMAN OK
0547 PM CST SUN DEC 14 2008
AREAS AFFECTED...SWRN MO/FAR NWRN AR TO CNTRL IL/FAR ERN IA
CONCERNING...WINTER MIXED PRECIPITATION
VALID 142347Z - 150345Z
A NARROW SWATH OF SHOWERS AND ISOLATED TSTMS PRODUCING FREEZING RAIN
AND/OR SLEET WILL LIKELY INCREASE IN THE WAKE OF AN ARCTIC COLD
FRONT PASSAGE. LIQUID EQUIVALENT PRECIPITATION RATES WHERE
TEMPERATURES ARE SUB-FREEZING SHOULD RANGE FROM 0.05 TO 0.15 IN PER
3-HR PERIOD.
ARCTIC COLD FRONT STRETCHED FROM ABOUT 20 W RFD TO 20 W MKO AT
23Z...WITH SEWD MOVEMENT AROUND 20 KTS /PER RECENT SURFACE
ANALYSES/. SHOWERS HAVE GRADUALLY INCREASED ON THE COOL SIDE OF THE
BOUNDARY...LIKELY AIDED BY 1) PLUME OF 50S SURFACE DEW POINTS
COLOCATED WITH STRONG LOW-LEVEL FRONTOGENESIS/MASS CONVERGENCE AND
2) ASCENT ASSOCIATED WITH MID-LEVEL SHORT WAVE EJECTING NEWD ACROSS
THE CNTRL PLAINS. SURFACE FREEZING LINE LAGS FRONTAL PASSAGE BY
ABOUT 50-75 NM...WITH BULK OF PRECIPITATION ATTM WITHIN THIS RANGE
/EXCEPT OVER ERN IA/. AFTERNOON MODEL GUIDANCE SUGGESTS
PRECIPITATION WILL GRADUALLY INCREASE WITHIN THE SUB-FREEZING
SURFACE AIR MASS AS CAA CONTINUES. THE SLOPED LOW-LEVEL THERMAL
GRADIENT WILL BE CONDUCIVE TO FREEZING RAIN WITHIN ABOUT A 20-40 NM
CORRIDOR BEFORE TRANSITIONING TO SLEET. ALTHOUGH OVERALL DURATION OF
ICE ACCUMULATIONS AT ANY ONE POINT SHOULD BE SHORT...GIVEN THE
PROGRESSIVE NATURE OF THE FRONT...CONVECTIVE PRECIPITATION RATES MAY
LOCALLY EXCEED 0.10 IN/HR AT TIMES.
..GRAMS.. 12/14/2008
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
...NOTICE...
SPC WINTER WEATHER MESOSCALE DISCUSSIONS WILL BE ISSUED ON A
SCHEDULED BASIS FROM DECEMBER 1 THROUGH FEBRUARY 28...FOUR
TIMES A DAY...AROUND 00 UTC...06 UTC...12 UTC...AND 18 UTC
FOR SIGNIFICANT SHORT RANGE WINTER WEATHER EVENTS.
ATTN...WFO...LOT...ILX...LSX...DVN...LZK...SGF...EAX...TSA...
LAT...LON 39148987 37109203 36179309 35919427 36139479 37149465
38099373 39839238 39929231 41239180 42149092 42348997
42218905 41508857 40368892 39148987
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