SWOMCD
SPC MCD 202332
WAZ000-ORZ000-210330-
MESOSCALE DISCUSSION 2492
NWS STORM PREDICTION CENTER NORMAN OK
0532 PM CST SAT DEC 20 2008
AREAS AFFECTED...W CNTRL WA AND ORE
CONCERNING...WINTER MIXED PRECIPITATION
VALID 202332Z - 210330Z
MIXED WINTER PRECIPITATION WILL TRANSITION TO FREEZING RAIN ACROSS
NWRN ORE IN VALLEY LOCATIONS NEAR SALEM AND PORTLAND. RATES NEAR
0.05 INCH PER HOUR ARE POSSIBLE. ELSEWHERE...HEAVY SNOW WILL
INCREASE ACROSS A BROADER AREA...WITH RATES NEAR 1 TO 2 INCHES AN
HOUR. SNOW WILL BE LIKELY EVEN IN VALLEY LOCATIONS...ALTHOUGH WITH
SMALLER RATES OF ACCUMULATION. INCREASING WINDS THROUGH FAVORED W-E
ORIENTED CANYONS AND PASSES WILL CAUSE BLOWING SNOW/WHITE OUT
CONDITIONS...ESPECIALLY CLOSER TO 06Z.
A VIGOROUS UPPER LOW AND SUBSTANTIAL MOISTURE CONTINUE TO MOVE
TOWARDS THE COAST. WARM ADVECTION HAS BEEN STEADILY INCREASING
THROUGH THE DAY...WITH VERY STRONG WAA NOTED FROM 0 TO 3 KM ON THE
PORTLAND VAD WIND PROFILER. RECENT ACARS SOUNDINGS INDICATE A WARM
NOSE BEGINNING TO DEVELOP JUST ABOVE THE SURFACE...WHICH SEEMS TO BE
SUPPORTED BY TEMPERATURE INCREASES ACROSS A FEW OBSERVATIONAL SITES
AROUND 4000 FT. HOWEVER...AN INCREASING PRESSURE GRADIENT WILL ALLOW
COLD ARCTIC AIR TO QUICKLY MOVE WWD THROUGH THE COLUMBIA RIVER GORGE
INTO VALLEY LOCATIONS NEAR PORTLAND. COOLING TEMPERATURES AT THE
SURFACE AND WARM AIR JUST ABOVE WILL ALLOW FOR FREEZING RAIN TO
DEVELOP...ALREADY REFLECTED WITH RECENT OBSERVATIONS AT SALEM
OREGON. RATES NEAR 0.05 INCH PER HOUR WILL BE LIKELY OVER THE NEXT
FEW HOURS. AROUND 03Z...THE APPROACHING SYSTEM WILL ALLOW WINDS TO
VEER AND TEMPERATURES TO INCREASE...AND MIXED PRECIPATION WILL BE
MORE LIKELY.
FARTHER N AND OVER THE OLYMPICS AND CASCADES...INITIAL THERMODYNAMIC
PROFILES THIS MORNING WERE SOMEWHAT DRY...BUT CONTINUED MOISTURE
ADVECTION AHEAD OF THE SYSTEM HAS ALLOWED SUBSTANTIAL
MOISTENING...AND SNOWFALL RATES HAVE ALREADY BEGUN TO INCREASE ALONG
THE WASHINGTON COAST. AN UPSLOPE REGIME AND A STRONG SLY/SWLY LOW
LEVEL JET WILL AID IN THE ASCENT OF MOIST AIR OVER COLD SURFACE
TEMPERATURES...WITH THE HIGHEST ACCUMULATIONS EXPECTED ACROSS THE
WRN SLOPES OF THE CASCADES. ALTHOUGH THE ERN SLOPES WILL HAVE
SOMEWHAT DRIER LOW LEVEL PROFILES IN DOWNSLOPING...SIGNIFICANT
ACCUMULATIONS WILL STILL BE LIKELY. FURTHERMORE...THE PRESSURE
GRADIENT WILL CONTINUE TO INCREASE AS COLD ARCTIC AIR REMAINS TO THE
LEE OF THE CASCADES...WHILE WARM MARITIME AIR PROGRESSES FROM THE W.
ELY WINDS WILL BE STRONGEST THROUGH FAVORED W-E ORIENTED CANYONS AND
PASSES...AND BLOWING SNOW WILL CREATE WHITE OUT CONDITIONS.
..HURLBUT/RACY.. 12/20/2008
...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...SEW...PQR...
LAT...LON 44522348 45802373 46642374 47242317 47522235 47062133
45622124 44632169 44012229 44162311 44522348
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
To unsubscribe from WX-STORM send e-mail to LISTSERV@LISTSERV.ILLINOIS.EDU with
"unsub wx-storm" in the body of your message. For more information write cnovy@cox.net.
No comments:
Post a Comment