MESO: Mesoscale Discussion 2544

ACUS11 KWNS 291112
SWOMCD
SPC MCD 291112
ORZ000-291415-

MESOSCALE DISCUSSION 2544
NWS STORM PREDICTION CENTER NORMAN OK
0512 AM CST MON DEC 29 2008

AREAS AFFECTED...MUCH OF THE OREGON CASCADES

CONCERNING...HEAVY SNOW

VALID 291112Z - 291415Z

HEAVY SNOW IS IN THE PROCESS OF DEVELOPING ACROSS HIGHER ELEVATIONS
OF THE OREGON CASCADES. SNOW RATES ARE EXPECTED TO INCREASE THROUGH
MID MORNING...AND PROBABLY WILL BE ENHANCED BY CONVECTIVE BURSTS.

A NARROW TONGUE OF MOISTURE...CHARACTERIZED BY PRECIPITABLE WATER
VALUES OF .75-1 INCH...IS ADVECTING NORTHWARD ALONG THE WESTERN
SLOPES OF THE OREGON CASCADES...AHEAD OF A VIGOROUS SHORT WAVE
IMPULSE RAPIDLY APPROACHING THE PACIFIC NORTHWEST COAST. MODELS
SUGGEST THAT A 110+ KT 500 MB JET STREAK ASSOCIATED WITH THIS
PERTURBATION WILL NOSE INLAND LATER THIS MORNING. THIS IS EXPECTED
TO BE ACCOMPANIED BY STRONG DYNAMIC MID-LEVEL COOLING...ASSOCIATED
WITH AGEOSTROPHIC FORCING IN THE EXIT REGION OF THIS
FEATURE...COUPLED WITH INCREASING OROGRAPHIC LIFT ASSOCIATED WITH A
STRENGTHENING UPSLOPE COMPONENT ALONG THE WESTERN MOUNTAIN SLOPES.
AND...STEEPENING MID-LEVEL LAPSE RATES WILL LIKELY PROMOTE
INCREASING/DEEPENING CONVECTION CAPABLE OF PRODUCING HEAVY SNOW
BURSTS. OCCASIONAL LIGHTNING STRIKES MAY ACCOMPANY ACTIVITY WHICH
COULD...AT LEAST BRIEFLY...YIELD SNOW RATES WELL IN EXCESS OF 2
INCHES PER HOUR. THIS MAY COMMENCE AS EARLY AS THE 13-15Z TIME
FRAME...THEN CONTINUE THROUGH LATE MORNING...BEFORE PRECIPITATION
BECOMES MORE SHOWERY IN THE WAKE OF THE UPPER IMPULSE BY/SHORTLY
AFTER 18Z. SNOW LEVELS MAY REMAIN STEADY OR RISE A BIT IN 3000-4000
FOOT RANGE...BEFORE LOWERING NEAR OR BELOW 3000 FEET TOWARD MID DAY.

..KERR.. 12/29/2008

...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...MFR...PQR...

LAT...LON 45322275 45382232 45292196 44692193 43472253 43192264
43122314 43342357 44392316 44822292 45322275

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