SPC MD 257

MD 0257 CONCERNING WINTER MIXED PRECIPITATION FOR PORTIONS OF NWRN NEB NEWD INTO NERN SD


MESOSCALE DISCUSSION 0257
NWS STORM PREDICTION CENTER NORMAN OK
0456 AM CST SAT MAR 09 2013

AREAS AFFECTED...PORTIONS OF NWRN NEB NEWD INTO NERN SD

CONCERNING...WINTER MIXED PRECIPITATION

VALID 091056Z - 091600Z

SUMMARY...WINTER MIXED PRECIPITATION WILL INCREASE IN COVERAGE THIS
MORNING...WITH SNOW BECOMING THE PREDOMINANT PRECIPITATION TYPE
ACROSS NWRN NEB AND SWRN/S-CNTRL SD BY 16-17Z.

DISCUSSION...AN ARC OF CONVECTION WITH POSSIBLE THUNDERSTORMS FROM
N-CNTRL NEB INTO NWRN NEB WILL CONTINUE TO ADVANCE NWD DURING THE
NEXT FEW HOURS. THIS ACTIVITY RESIDES WITHIN A ZONE OF MID-LEVEL
WAA/ISENTROPIC ASCENT WELL IN ADVANCE OF A DEEP CLOSED LOW NEAR THE
FOUR-CORNERS REGION. AS THIS ACTIVITY MOVES OVER SUB-FREEZING SFC
TEMPERATURES...FREEZING RAIN WILL LIKELY OCCUR ACROSS PARTS OF
CHERRY AND SHERIDAN COUNTIES NEB AND INTO ADJACENT S-CNTRL SD
THROUGH AT LEAST 1230Z. SLEET OR SNOW MAY OCCUR FARTHER N INTO SD AS
THE PRECIPITATION ENCOUNTERS RELATIVELY COOLER ELEVATED WARM NOSE
TEMPERATURES PER FORECAST SOUNDINGS.

ADDITIONAL PRECIPITATION WILL LIKELY DEVELOP ACROSS THE AREA THROUGH
THE MORNING. THIS WILL OCCUR AS AN 850-500-MB FRONTOGENETIC
CIRCULATION STRENGTHENS WHILE MULTIPLE MID-LEVEL IMPULSES TRACK
DOWNSTREAM OF THE LOW...AND THE IMPULSES INTERACT WITH A BACKGROUND
LOW/MID-LEVEL BAROCLINIC ZONE. A MIX OF PRECIPITATION TYPES WILL
LIKELY ENSUE...INCLUDING FREEZING RAIN...SLEET...AND SNOW...AND
THUNDERSTORMS WILL ALSO BE POSSIBLE WITH ENHANCED PRECIPITATION
RATES. FREEZING RAIN RATES OF 0.05-0.10 IN/HR WILL BE POSSIBLE WITH
THE STRONGEST CONVECTION.

WITH TIME...AS A STRONG COLD SURGE OCCURS E OF THE ROCKIES AND SFC
LOW PRESSURE DEEPENS OVER NWRN KS AND SWRN NEB...LOW-LEVEL COLD
ADVECTION WILL SUPPORT SNOW BECOMING THE PREDOMINANT PRECIPITATION
TYPE ACROSS NWRN NEB AND SWRN/S-CNTRL SD BY 16-17Z...WHILE MIXED
PRECIPITATION PERSISTS FARTHER NE. SNOWFALL RATES OF 1 IN/HR WILL BE
POSSIBLE...ESPECIALLY AFTER 14Z.

..COHEN.. 03/09/2013

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

ATTN...WFO...FSD...ABR...LBF...UNR...CYS...

LAT...LON   42650315 44310035 45249827 45409668 45019690 44239807
            43419946 42520098 41640210 41070303 41230400 42650315

via SPC Forecast Products http://www.spc.noaa.gov/products/md/md0257.html