MESO: Mesoscale Discussion 2143

ACUS11 KWNS 290059
SWOMCD
SPC MCD 290058
CAZ000-290700-

MESOSCALE DISCUSSION 2143
NWS STORM PREDICTION CENTER NORMAN OK
0658 PM CST TUE DEC 28 2010

AREAS AFFECTED...SIERRA NEVADA MOUNTAINS

CONCERNING...HEAVY SNOW

VALID 290058Z - 290700Z

SNOWFALL RATES OF 2 IN/HR ARE FORECAST TO DEVELOP AT ELEVATIONS
ABOVE 4000-5000 FT OVER THE NRN SIERRA NEVADA MOUNTAINS DURING THE
03-06Z TIME PERIOD...AND THEN SPREAD SWD INTO THE SRN SIERRA NEVADA
MOUNTAINS BY 06-09Z...WHERE RATES UP TO 3 IN/HR WILL BE POSSIBLE.

WV IMAGERY SHOWS AN UPPER-LEVEL S/W TROUGH LOCATED 400-500 MILES NW
OF THE PAC NW COAST AT 00Z...WITH A SECOND DISTURBANCE AND
ASSOCIATED WLY UPR JET /SPEEDS AT 9 KM AGL AROUND 120 KT BASED ON
BHX VWP/ POSITIONED TO ITS S. IN ADDITION...SATELLITE DERIVED PW
GUIDANCE INDICATES A PROMINENT ATMOSPHERIC RIVER OF MOISTURE BEING
TRANSPORTED EWD INTO NRN CA...CHARACTERIZED BY PWAT VALUES SEVERAL
STANDARD DEVIATIONS ABOVE NORMAL FOR THE REGION AND TIME OF YEAR. AS
THE NRN STREAM DISTURBANCE CONTINUES TO DIGS SEWD TOWARD THE ORE/WA
COAST DURING THE NIGHT...THE WLY MID/UPPER LEVEL JET AND STRONG
MOISTURE TRANSPORT REGIME WILL SHIFT SWD ACROSS THE NRN SIERRA
NEVADA MOUNTAINS DURING THE 03-06Z TIME PERIOD...AND THEN THE SRN
SIERRA MOUNTAINS BY 06-09Z. THE COMBINATION OF STRONG LARGE-SCALE
ASCENT ASSOCIATED WITH THE APPROACHING UPPER TROUGH...AND MOIST
UPSLOPE AUGMENTATION ALONG THE WINDWARD SIDE OF THE MOUNTAINS...ARE
EXPECTED TO YIELD AN ENVIRONMENT FAVORABLE FOR WIDESPREAD 2 IN/HR
SNOWFALL RATES ABOVE 4000-5000 FT...WITH 3 IN/HR RATES LOCALLY
POSSIBLE OVER PORTIONS OF THE SRN SIERRA...WHERE WINDS WILL BE MORE
PERPENDICULAR TO THE MOUNTAIN RANGE.

..GARNER.. 12/29/2010

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

ATTN...WFO...VEF...REV...HNX...STO...

LAT...LON 40442175 40692172 40762130 38991999 38441953 37141842
36171828 35971861 36571889 38112031 38882058 39912148
40442175

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