MESO: Mesoscale Discussion 2263

ACUS11 KWNS 271829
SWOMCD
SPC MCD 271828
WAZ000-ORZ000-CAZ000-272200-

MESOSCALE DISCUSSION 2263
NWS STORM PREDICTION CENTER NORMAN OK
1228 PM CST THU DEC 27 2007

AREAS AFFECTED...WRN ORE/WRN WA

CONCERNING...HEAVY SNOW

VALID 271828Z - 272200Z

SNOW RATES OF 1 INCH PER HOUR ARE POSSIBLE IN THE LOWER ELEVATIONS
OF WRN ORE/WA THIS AFTERNOON...WITH RATES OF 2 INCHES PER HOUR IN
THE HIGHER TERRAIN.

SATELLITE IMAGERY/SHORT-RANGE MODELS ARE IN GOOD AGREEMENT WITH THE
LOCATION AND INTENSITY OF A VIGOROUS SHORTWAVE TROUGH CURRENTLY
MOVING SEWD ALONG BC COAST. THE MAXIMUM IN SYNOPTIC-SCALE ASCENT
SHOULD REACH THE COASTAL RANGE OF WA/ORE AT 21 UTC...AND RESIDE OVER
THE CASCADE MTNS AROUND 00 UTC PER THE LATEST SREF. THE 12 UTC SLE
RAOB INDICATED A FREEZING LEVEL OF 1100 FEET MSL...BUT SUBSTANTIAL
VEERING OF THE LOWER/MIDDLE TROPOSPHERIC WIND PROFILE IMPLIES A
GRADUAL RISE SHOULD OCCUR THROUGH THE DAY. A CLOSE EXAMINATION OF
THE NAM FORECAST SOUNDINGS SHOWS THE FREEZING LEVEL AT 1600-1700
FEET MSL BY LATE THIS AFTERNOON...AND STRONG ASCENT THROUGH THE
DENDRITIC CRYSTAL GROWTH ZONE. THE SNOW LEVEL SHOULD THEREFORE RISE
TO 600-1200 FEET MSL...ALTHOUGH A NOTABLE EXCEPTION MAY BE THE NRN
WILLAMETTE VALLEY/PDX METRO AREA WHERE A WEAK ELY COMPONENT OF THE
LOW-LEVEL FLOW WILL MAINTAIN A SLIGHTLY LOWER SNOW LEVEL. THE HIGHER
ELEVATIONS AROUND PDX AND THE ERN PDX METRO AREA WILL LIKELY SEE THE
PRECIPITATION TYPE REMAIN ENTIRELY SNOW. IN TERMS OF TIMING...THE
HIGH-RESOLUTION WINDOW RUNS /WRF-NMM AND WRF-ADW/ AND THE 09 UTC
SREF ARE IN EXCELLENT AGREEMENT DEPICTING SNOW RATES OF 1 INCH PER
HOUR /AND 2 INCHES PER HOUR IN THE HIGHER TERRAIN/ OVER THE COASTAL
RANGE AT 21 UTC...AND PEAKING OVER THE CASCADE MOUNTAINS AT 00 UTC.

.BRIGHT.. 12/27/2007

..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...PDT...MFR...SEW...PQR...EKA...

43432428 46062401 47592433 48212412 47052171 45232132
43392146 42592166 41842237 41882365

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