MESO: Mesoscale Discussion 0248

ACUS11 KWNS 170535
SWOMCD
SPC MCD 170534
WIZ000-ILZ000-IAZ000-171030-

MESOSCALE DISCUSSION 0248
NWS STORM PREDICTION CENTER NORMAN OK
1134 PM CST SAT FEB 16 2008

AREAS AFFECTED...CENTRAL/EASTERN IA AND SOUTHERN WI/FAR NORTHERN IL

CONCERNING...FREEZING RAIN

VALID 170534Z - 171030Z

FREEZING RAIN IS EXPECTED TO INCREASE OVERNIGHT ACROSS SOUTH
CENTRAL/EAST CENTRAL/NORTHEAST IA INTO SOUTHERN WI/EXTREME NORTHERN
IL...WITH ICE ACCUMULATIONS POSSIBLE THROUGH SUNRISE.

OWING TO AMPLE LARGE SCALE FORCING FOR ASCENT DOWNSTREAM OF
NORTHEAST-TRANSITIONING SOUTH CENTRAL PLAINS CYCLONE...REGIONAL
RADAR MOSAIC TRENDS REFLECT A NORTHWARD EXPANSION OF PRECIPITATION
INTO SOUTHERN IA/NORTHERN IL OVER THE PAST SEVERAL HOURS. AS THIS
TREND CONTINUES OVERNIGHT...FREEZING RAIN IS EXPECTED TO EXPAND
NORTHWARD/INCREASE OVERNIGHT ACROSS PORTIONS OF CENTRAL/EASTERN IA
AND EXTREME NORTHERN IL INTO SOUTHERN WI. A SHALLOW SUB-FREEZING
LAYER EXISTS ACROSS THE REGION PER SURFACE NETWORK OBSERVATIONS AND
00Z OBSERVED DAVENPORT IA RAOB AND MORE RECENT REGIONAL TAMDAR/ACARS
SOUNDINGS FROM LA CROSSE/MOLINE/ROCKFORD. ATOP THIS SUB-FREEZING
BOUNDARY LAYER...AN ELEVATED WARM LAYER OF 3-7C BASED AROUND 850-900
MB WILL BE SUFFICIENT FOR FULL MELTING ALOFT AS SATURATION OCCURS
OVERNIGHT. THIS IDEA IS WELL SUPPORTED BY 00Z NAM/03Z RUC FORECAST
SOUNDINGS THROUGH DAYBREAK...AS WELL AS 21Z SREF PRECIP TYPE
PROBABILITIES. THUS IT APPEARS FREEZING RAIN WILL BE THE DOMINANT
PRECIPITATION TYPE OVERNIGHT ACROSS PORTIONS OF SOUTH CENTRAL/EAST
CENTRAL/NORTHEAST IA...INCLUDING A CORRIDOR FROM DES MOINES TO CEDAR
RAPIDS/WATERLOO/DUBUQUE...INTO MUCH OF SOUTHERN WI INCLUDING THE
LONE ROCK/MADISON VICINITIES. ICE ACCUMULATIONS ARE POSSIBLE WHERE
SUB-32F SURFACE TEMPERATURES WILL BE MAINTAINED THROUGH EARLY
MORNING.

.GUYER.. 02/17/2008

..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...MKX...DVN...ARX...DMX...

43858869 43698796 42438823 42079024 41319232 40639398
41109456 42489318 43499118

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