SWOMCD
SPC MCD 270021
ORZ000-WAZ000-270515-
MESOSCALE DISCUSSION 0088
NWS STORM PREDICTION CENTER NORMAN OK
0621 PM CST SAT JAN 26 2008
AREAS AFFECTED...COLUMBIA RIVER VALLEY/BASIN OF NRN ORE/SRN
WA...NRN/CENTRAL ORE CASCADES
CONCERNING...WINTER MIXED PRECIPITATION
VALID 270021Z - 270515Z
FREEZING RAIN WILL CONTINUE TO DEVELOP OVER MUCH OF THE COLUMBIA
RIVER BASIN THROUGH THE EVENING HOURS. FURTHER WEST...FREEZING RAIN
IS EXPECTED TO CHANGE OVER TO RAIN OVER THE COLUMBIA GORGE BY 04Z.
HEAVY SNOW IS ALSO EXPECTED TO DEVELOP OVER THE CENTRAL/NRN OREGON
CASCADES THIS EVENING...WITH HRLY RATES OVER 1 INCH PER HR ON WEST
FACING SLOPES.
LATEST RADAR IMAGERY INDICATES THAT PRECIPITATION CONTINUES TO
EXPAND IN AREAL COVERAGE OVER THE COLUMBIA RIVER BASIN AS LOW LEVELS
CONTINUE TO SATURATE OWING TO STRONG WAA /EVIDENT BY 1 MB/HR SFC
PRESSURE FALLS AND PDT VWP DATA/. RAWS/ASOS DATA IN AND AROUND THE
COLUMBIA RIVER BASIN INDICATES THAT TOP THE SHALLOW SUBFREEZING
AIRMASS IS AROUND 2000-2500 FT...AND THAT THE ELEVATED WARM LAYER
WAS AROUND 2500 FT DEEP. A CONTINUATION OF STRONG WAA SHOULD
GRADUALLY ERODE THE DEPTH OF THIS LAYER...BUT SEVERAL MORE HRS OF
LIGHT TO OCCASIONALLY MODERATE FREEZING RAIN IS EXPECTED. WHERE THE
TEMPERATURES ARE AROUND 32 F AT 00Z /COLUMBIA RIVER GORGE/ FREEZING
RAIN IS EXPECTED TO CHANGEOVER TO RAIN BY 04Z AS THE ELY SFC
GRADIENT THAT EXISTED EARLIER TODAY CONTINUES TO DIMINISH LIMITING
DRY AIR ENTRAINMENT INTO THIS AREA.
FURTHER SOUTHWEST...WV IMAGERY SHOWS A WELL DEFINED SHORTWAVE OFF
THE WA/ORE COAST. THE COMBINATION OF INCREASING LIFT IN THE MID
LEVELS AHEAD OF THIS FEATURE...STRONG/VEERING 850 MB WINDS /ALREADY
EVIDENT ON THE PORTLAND VWP/ AND LOW LEVEL COOLING SHOULD SUPPORT
INCREASING SNOWFALL RATES AND LOWERING SNOW LEVELS ACROSS THE
NRN/CENTRAL ORE CASCADES AFTER 03Z. OVER 1 INCH/HR SNOWFALL RATES
ARE POSSIBLE ABOVE 3500 FT.
.CROSBIE.. 01/27/2008
..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...OTX...PDT...MFR...PQR...
46272055 46082157 45582271 45092300 43412316 43132260
43882209 44932172 45311954 45491873 45771809 46231781
46691818 46861852 46791955 46422012
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