SWOMCD
SPC MCD 010629
IAZ000-NEZ000-SDZ000-WYZ000-011000-
MESOSCALE DISCUSSION 2170
NWS STORM PREDICTION CENTER NORMAN OK
1229 AM CST SAT DEC 01 2007
AREAS AFFECTED...FAR SERN WY....MUCH OF NRN/CNTRL NEB...SRN SD
CONCERNING...WINTER MIXED PRECIPITATION
VALID 010629Z - 011000Z
A MIX OF SLEET/FREEZING RAIN/SNOW WILL DEVELOP AS LOW/MID-LEVEL
ASCENT STRENGTHENS OVERNIGHT. THERMODYNAMIC PROFILES APPEAR TO FAVOR
MAINLY SLEET ACROSS NEB...WITH A TRANSITION TO FREEZING RAIN LIKELY
OCCURRING ALONG AND JUST N OF THE I-80 CORRIDOR TOWARDS 12Z. ACROSS
S-CNTRL/SERN SD...PTYPE IS MORE UNCERTAIN WITH EITHER SNOW OR SLEET
BECOMING MODERATE IN INTENSITY BY 12Z.
RECENT SATELLITE IMAGERY DEPICTS COOLING CLOUD TOPS ARCING FROM THE
SRN ROCKIES ONTO THE CNTRL SRN HIGH PLAINS INDICATIVE OF
STRENGTHENING ASCENT DOWNSTREAM OF LARGE-SCALE TROUGH OVER THE WRN
CONUS. LATEST SHORT-TERM MODEL FORECAST GUIDANCE INDICATES RAPID
STRENGTHENING OF 850 TO 700 MB S/SWLY FLOW ACROSS THE CNTRL PLAINS
WITH INCREASING FRONTOGENETICAL FORCING BECOMING CENTERED FROM THE
NEB PANHANDLE E/NEWD TOWARDS SERN SD/NERN NEB. THE END RESULT SHOULD
BE A FOCUSED AXIS OF WINTERY PRECIPITATION COMMENCING BY
09Z...INCREASING IN INTENSITY/COVERAGE TOWARDS DAYBREAK.
THERE IS SOME UNCERTAINTY IN EXPECTED PTYPE GIVEN THAT REGIONAL 00Z
RAOBS INDICATED WET-BULB TEMPERATURES AOB FREEZING THROUGHOUT THE
ATMOSPHERIC COLUMN. MODEL FORECAST SOUNDINGS AND SREF PROBABILISTIC
GUIDANCE SEEM TO FAVOR SLEET AS THE PREDOMINANT PTYPE WITH A
TRANSITION TO FREEZING RAIN ALONG THE SRN PORTION OF THE MD AREA
OWING TO INTENSE WARM/MOIST ADVECTION IN THE LOW-LEVELS. FARTHER N
ACROSS S-CNTRL/SERN SD...INITIAL SNOW MAY TRANSITION TO A MIX OF
SNOW/SLEET WITH TIME.
.GRAMS.. 12/01/2007
..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...FSD...OAX...ABR...GID...LBF...UNR...GLD...CYS...
42969622 42169590 41479590 41409726 41319824 40929934
40320004 40320077 40720158 41180232 41320310 41400387
41690455 42020491 42710473 43210373 43880151 44149849
44129732 43739672
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