Snow Advisory 9, NWS Pendleton, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
225 PM PST WED DEC 7 2005

.SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT...AN UPPER LEVEL
DISTURBANCE CROSSING INTO SOUTHWEST OREGON WILL SEND MOISTURE INTO
CENTRAL AND NORTH CENTRAL OREGON THIS EVENING.  A WEB CAM AT SUN
RIVER INDICATES THAN ABOUT A HALF INCH OF SNOW HAS ALREADY FALLEN.
ADDITIONAL SNOW ACCUMULATIONS OF AROUND AN INCH CAN BE EXPECTED THIS
EVENING IN CENTRAL OREGON...WITH SCATTERED SNOW SHOWERS WITH LITTLE
OR NO SNOW ACCUMULATION IN NORTH CENTRAL OREGON.  THIS SYSTEM WILL
DROP SOUTH ON THURSDAY BRINGING DRYING CONDITIONS TO THESE AREAS.

MEANWHILE...MODIFIED ARCTIC AIR HAS SPILLED INTO THE COLUMBIA BASIN
AND SURROUNDING VALLEYS.  A SURFACE LOW OVER SOUTHWEST OREGON IS
AIDING IN DRAWING THIS COLD AIR SOUTHWEST INTO CENTRAL AND NORTH
CENTRAL OREGON AS WELL WHERE TEMPERATURES HAVE REMAINING BELOW
FREEZING THROUGHOUT THE DAY.  NORTHERLY PRESSURE GRADIENTS WILL KEEP
COLD AIR FILTERING INTO THESE AREAS THROUGH TOMORROW WITH AREAS OF
FREEZING FOG TONIGHT AND PATCHY FREEZING FOG ON THURSDAY.  SOME
PATCHY FREEZING FOG MAY ALSO OCCUR TOMORROW ALONG AREA RIVERS IN THE
COLUMBIA BASIN...AS WELL AS NEAR THE BASE OF THE BLUE MOUNTAINS.
UPPER LEVEL HIGH PRESSURE WILL BUILD INTO THE AREA THURSDAY NIGHT
THROUGH FRIDAY NIGHT.  THIS WILL RESULT IN WARMING TEMPERATURES
ALOFT...WHILE COLD AIR REMAINS TRAPPED IN THE VALLEYS.  THIS WILL
RESULT IN STRENGTHENING TEMPERATURE INVERSIONS AND WILL LEAD TO
INCREASING AREAS OF FREEZING FOG AND LOW STRATUS WITH TIME ACROSS
THE COLUMBIA BASIN AND SURROUNDING VALLEY/FOOTHILL LOCATIONS...AS
WELL AS NORTH CENTRAL AND CENTRAL OREGON.  JW

.LONG TERM...SATURDAY THROUGH WEDNESDAY...GFS/ECMWF IN AGREEMENT
THROUGH EARLY NEXT WEEK...WITH A STRONG RIDGE BUILDING ACROSS THE
REGION. INVERSIONS WILL BE STRONGEST SATURDAY THROUGH MONDAY AS BOTH
THE SURFACE AND UPPER LEVEL RIDGES ARE OVERHEAD. WILL INCREASE FOG
COVERAGE TO AREAS AND EXPAND THE AREAL COVERAGE TO INCLUDE MOST
ELEVATIONS BELOW 2500-3000 FEET. WILL ALSO KEEP DAYTIME TEMPERATURES
QUITE LOW IN THESE AREAS...BELOW FREEZING FOR THE MOST PART...SO A
SIGNIFICANT FREEZING FOG EVENT IS POSSIBLE. MTN LOCATIONS WILL SEE
SOME WARMUP ABOVE THE INVERSION...BUT WITH MOST OF THESE AREAS
HAVING SNOW COVER...THE WARMUP WILL BE TEMPERED DURING THE DAY...AND
RADIATIONAL COOLING WILL BE SUBSTANTIAL AT NIGHT. GFS/ECMWF HINT AT
A POSSIBLE BREAKDOWN OF THE RIDGE BY MIDWEEK...BUT WITH EACH RUN
DELAYING THIS POSSIBILITY...WILL KEEP THE RIDGE SOLUTION THROUGH
WEDNESDAY.

&&

.AVIATION...VFR CONDITIONS WILL PREVAIL AT KPSC/KYKM/KDLS FOR THE
NEXT 24 HOURS. FOR KRDM...VLIFR CONDITIONS WILL LIKELY GIVE WAY TO
IFR CONDITIONS AS LOW PRESSURE CLIPS THE REGION...WITH THE VERY LOW
CLOUD DECK/FOG RETURNING LATE TONIGHT AS THE PRECIPITATION EXITS TO
THE SOUTH. FOR KALW...THE FOG THAT WAS OVER THE AREA THIS MORNING
WAS PUSHED EASTWARD...WITH A LOW CLOUD DECK REMAINING. THIS DECK
WILL REMAIN OVER THE AREA...WITH PERHAPS SOME BRIEF PERIODS OF
SCATTERING OUT LATE THIS AFTN. THE FOG WILL RETURN OVERNIGHT...WITH
VISIBILITIES REDUCED TO LESS THAN 1/2 MILE THURSDAY MORNING. KPDT
WILL HAVE PERIODS OF BROKEN LOW CLOUDS AS WELL LATE THIS AFTN BEFORE
VFR CONDITIONS PREVAIL OVERNIGHT.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  15  27  16  28 /   0   0   0   0
ALW  17  26  17  28 /   0   0   0   0
PSC  15  30  14  29 /   0   0   0   0
YKM  18  30  15  32 /   0   0   0   0
HRI  16  30  14  29 /   0   0   0   0
ELN  15  30  14  31 /   0   0   0   0
RDM  20  28  17  32 /  60  20   0   0
LGD  15  24  16  29 /   0   0   0   0
5J0  16  33  11  34 /  10  10   0   0
DLS  25  33  22  36 /  10   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&

TI:GGG
FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON
86/89/89

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