FXUS66 KPDT 242244
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
244 PM PST THU DEC 24 2009
.SHORT TERM...TONIGHT THROUGH SUNDAY...HIGH PRESSURE WILL REMAIN
ENTRENCHED OVER THE AREA THROUGH SATURDAY. THIS WILL LEAD TO A
STRENGTHENING INVERSION OVER THE REGION FOR AT LEAST THE NEXT COUPLE
OF DAYS. THE CURRENT AIR STAGNATION ADVISORY WILL LIKELY REMAIN IN
PLACE THROUGH SATURDAY AFTERNOON. SEE PRODUCT PDXNPWPDT FOR DETAILS.
THE MAIN FORECASTING CHALLENGE WILL BE THE PRESENCE OF LOW CLOUDS
AND FREEZING FOG IN THE COLUMBIA BASIN...ADJACENT VALLEYS AND NORTH
CENTRAL OREGON AT LEAST AS FAR SOUTH AS MADRAS. STRATUS HAS ALREADY
BEGIN TO DEVELOP AT AROUND 2000 FEET ALONG THE EDGES OF THE COLUMBIA
BASIN AND EXPECT THE COVERAGE WILL INCREASE OVERNIGHT. FREEZING FOG
HAS DEVELOPED AT THE WALLA WALLA AIRPORT AND EXPECT THAT TO EXPAND
OVERNIGHT TO OTHER PORTIONS OF THE COLUMBIA BASIN AS WELL. ONCE THE
FOG AND STRATUS FORMS...SEE LITTLE TO DISLODGE IT UNTIL A WEAK
SYSTEM MOVES IN FROM THE SOUTH LATE SATURDAY NIGHT AND SUNDAY. EVEN
AT THAT THE MODELS ARE SHOWING AT BEST MARGINAL STRENGTH TO SCOUR
OUT THE COLD AIR AT THE SURFACE. EXPECT THAT THE STRATUS AND FOG
WILL PERSIST THROUGH SUNDAY WITH PERHAPS SOME WEAKENING. THE SYSTEM
ON SATURDAY NIGHT AND SUNDAY WILL BRING SOME LIGHT SNOW SHOWERS TO
CENTRAL OREGON AND THE OCHOCO-JOHN DAY HIGHLANDS AS WELL ...BUT ONLY
MINOR ACCUMULATIONS ARE ANTICIPATED. TEMPERATURES FOR THE NEXT FEW
DAYS WILL BE DECIDEDLY COOL WITH ONLY CENTRAL OREGON...THE JOHN DAY
BASIN AND PERHAPS THE COLUMBIA GORGE WARMING ABOVE FREEZING. NIGHT
TIME TEMPERATURES WILL GENERALLY BE IN THE 10 TO 20 RANGE...A LITTLE
COOLER IN HIGHER MOUNTAIN VALLEYS THAT WILL BE ABOVE THE CLOUDS FOR
THE MOST PART. WINDS WILL BE LIGHT THROUGH THE PERIOD. PERRY
.LONG TERM...SUNDAY NIGHT THROUGH THURSDAY. A WEAK SYSTEM MOVES
THROUGH THE AREA MONDAY FOLLOWED BY ANOTHER ONE WEDNESDAY. THESE
SHOULD BRING LIGHT PRECIPITATION. A STRONGER SYSTEM WILL IMPACT THE
PACIFIC NORTHWEST THURSDAY WITH A BETTER CHANCE OF RAIN AND SNOW.
LOW LEVEL LAPSE RATES OFF THE GFS SUGGEST THE STRATUS AND FOG WILL
DISSIPATE ON TUESDAY. THE AIRMASS WILL REMAIN FAIRLY COLD THROUGH
THE PERIOD WITH TEMPERATURES BELOW NORMAL. SOME WARMING WILL LIKELY
OCCUR BY THURSDAY WITH WARM ADVECTION ASSOCIATED WITH THE OFFSHORE
STORM. WINDS WILL ALSO BE LIGHT THROUGH THE PERIOD POSSIBLY
INCREASING ON THURSDAY. 94
&&
.AVIATION...PREVIOUS AVIATION DISCUSSION...18Z TAFS. SOME CLOUDS
ALONG THE EAST SLOPES OF THE CASCADES TODAY WILL IMPACT YKM DLS WITH
CEILINGS 020-040. ALSO SOME LOW CLOUDS AND FOG IN THE COLUMBIA BASIN
IMPACTING PDT ALW. THE REMAINDER OF THE TAF SITES WILL BE MAINLY
CLEAR WITH CIRRUS AT TIMES TODAY. STRONG LOW LEVEL INVERSIONS WILL
LEAD TO INCREASED FOG AND LOW CLOUD DEVELOPMENT TONIGHT. WILL LIKELY
SEE MORE WIDESPREAD IFR AND LIFR LATE TONIGHT AND FRIDAY MORNING.
SURFACE WINDS REMAIN LESS THAN 10 KT. 94
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 17 27 19 29 / 0 0 0 0
ALW 19 26 20 29 / 0 0 0 0
PSC 18 29 20 31 / 0 0 0 0
YKM 16 28 18 31 / 0 0 0 0
HRI 18 30 19 30 / 0 0 0 0
ELN 16 28 17 30 / 0 0 0 0
RDM 13 37 14 37 / 0 0 0 0
LGD 12 31 15 31 / 0 0 0 0
GCD 17 36 17 36 / 0 0 0 0
DLS 21 33 22 35 / 0 0 0 0
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL 4 PM PST SATURDAY FOR ORZ041>044-
049-501-504-505.
WA...AIR STAGNATION ADVISORY UNTIL 4 PM PST SATURDAY FOR WAZ024-
026>029-501-502.
&&
THREAT INDEX
FRIDAY : GREEN
SATURDAY : GREEN
SUNDAY : GREEN
GREEN: NONE OR LIMITED NEED FOR WATCHES, WARNINGS, OR ADVISORIES.
YELLOW: A FEW WATCHES, WARNINGS, OR ADVISORIES POSSIBLE OR IN EFFECT.
RED: NUMEROUS WATCHES, WARNINGS, OR ADVISORIES POSSIBLE OR IN EFFECT.
FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON
$$
83/94/94
