SWOMCD
SPC MCD 212317
WAZ000-ORZ000-220315-
MESOSCALE DISCUSSION 2500
NWS STORM PREDICTION CENTER NORMAN OK
0517 PM CST SUN DEC 21 2008
AREAS AFFECTED...ORE CASCADES
CONCERNING...HEAVY SNOW
VALID 212317Z - 220315Z
SNOWFALL RATES WILL INCREASE DRAMATICALLY...ESPECIALLY ACROSS THE
ORE CASCADES THROUGH MID-EVENING WITH HOURLY RATES OF 1-2".
SFC LOW AROUND 350NM WNW OF KPDX AT 22Z IS EXPECTED TO DIG SEWD THIS
EVENING. ASSOCD OCFNT WAS ARRIVING ONSHORE WITH A HEALTHY BAND OF
PCPN SPREADING INLAND. HEAVIEST PCPN RATES APPEAR TO BE OCCURRING
ACROSS THE CSTL ZONES OF NWRN ORE/SWRN WA LATE THIS AFTN. LATEST
NAM GUIDANCE SUGGESTS THAT THE 95 KT H5 JET WILL SINK INTO NRN CA
WITH STRONGEST UPR DIVERGENCE SPREADING INTO WRN/CNTRL ORE WITH TIME
THIS EVENING. EXPECT THAT THE STRONGEST LARGE SCALE UVV WILL BOOST
UPSLOPE MOST FAVORABLY ACROSS THE ORE CASCADES THROUGH MID-EVENING.
HEAVIEST SNOWFALL SHOULD FALL GENERALLY IN THE 00-06Z TIME FRAME.
ELSEWHERE...LIGHTER...BUT STILL SIGNIFICANT SNOWFALL WILL OCCUR
ACROSS WRN/CNTRL WA...LIKELY PEAKING EARLY THIS EVENING. THE LWR
COLUMBIA RVR VLY AND PORTLAND ORE AREAS...SUFFICIENT WARM AIR JUST
ABOVE THE SHALLOW ARCTIC BOUNDARY LAYER WILL KEEP A RISK FOR ZR THIS
EVENING BEFORE TURNING TO SNOW AS THE COLUMN COOLS WITH THE APCH OF
THE PRIMARY UPR LOW.
..RACY.. 12/21/2008
...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...PDT...MFR...SEW...PQR...
LAT...LON 42892291 44742317 46282292 46652233 46662178 46502119
45182100 43532140 42582166 42392229 42892291
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