MESO: Mesoscale Discussion 2066

ACUS11 KWNS 050032
SWOMCD
SPC MCD 050031
MTZ000-WYZ000-050630-

MESOSCALE DISCUSSION 2066
NWS STORM PREDICTION CENTER NORMAN OK
0731 PM CDT SUN OCT 04 2009

AREAS AFFECTED...CENTRAL-NRN WY AND SRN MT

CONCERNING...HEAVY SNOW

VALID 050031Z - 050630Z

SNOWFALL RATES OF 1-2 IN/HR ARE FORECAST TO BECOME MORE PROBABLE
OVER PORTIONS OF CENTRAL-NRN WY AND SRN MT DURING THE
OVERNIGHT...WITH LOCALLY HIGHER RATES POSSIBLE ALONG ERN SLOPES OF
NORTH-SOUTH MOUNTAIN RANGES.

SHORT TERM MODEL GUIDANCE INDICATES THAT A 100+ KT H25 JET WILL
BEGIN TO SPREAD DOWNSTREAM OF A CLOSED UPPER LOW POSITIONED OVER THE
NRN GREAT BASIN. AS THIS OCCURS...THE UPPER TROUGH WILL BEGIN TO
OPEN UP SLIGHTLY AND LIFT ENE. AS A RESULT...LARGE SCALE LIFT IS
FORECAST TO STRENGTHEN OVER NRN WY AND SRN MT...WITH THE STRONGEST
MESOSCALE ASCENT /LOW LEVEL CONVERGENCE AND WAA/ FORECAST TO BECOME
MAXIMIZED INVOF THE WY/MT BORDER TOWARD 06Z AS A 50 KT SLY 700 MB
SPEED MAX ENCOUNTERS ELY LOW LVL FLOW OVER MT. PRECIPITATION
INTENSITY IS EXPECTED TO INCREASE IN RESPONSE TO THESE
FEATURES...WITH SNOWFALL RATES OF 1-2 IN/HR INITIALLY EXPECTED OVER
PORTIONS OF CENTRAL-NRN WY BY 03Z...AND THEN SPREADING TOWARD AND
EVENTUALLY N OF THE WY/MT BORDER BETWEEN 06-09Z. IN ADDITION...LOCAL
OROGRAPHIC ENHANCEMENT OF SNOWFALL RATES IS POSSIBLE ALONG ERN
SLOPES OF NORTH-SOUTH MOUNTAIN RANGES /SUCH AS THE BIGHORNS IN NRN
WY AND ABSAROKA RANGE IN NWRN WY AND SWRN-SRN MT/ IN RESPONSE TO
ENELY LOW LEVEL FLOW. MODEL FORECAST SOUNDINGS INDICATE A SHALLOW
SURFACE WARM LAYER WILL INITIALLY BE PRESENT OVER THE LOWER
ELEVATIONS...WITH SNOW LEVELS GENERALLY LOCATED ABOVE 5000 FT
MSL...BUT FALLING BELOW 5000 FT MSL AFTER 06Z IN RESPONSE TO DYNAMIC
AND UPSLOPE COOLING AS WELL AS EVAPORATIVE COOLING.

..GARNER.. 10/05/2009

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

ATTN...WFO...UNR...BYZ...RIW...

LAT...LON 46690746 46240535 45020454 43710556 43170891 43681027
44971086 46180986 46690746

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