FXUS66 KPDT 250539 AAA
AFDPDT
AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE PENDLETON OR
939 PM PST THU DEC 24 2009
UPDATED AVIATION DISCUSSION
.SHORT TERM...UPDATE...A HIGH AMPLITUDE UPPER RIDGE REMAINS ALONG
THE WEST COAST THIS EVENING. AS A RESULT THE PACIFIC NORTHWEST
REMAINS UNDER A NORTHERLY FLOW ALOFT. AREAS OF LOW CLOUDS AND FOG
DEVELOPED ALONG THE EAST SLOPES OF THE WASHINGTON CASCADES...THE
BLUE MOUNTAIN FOOTHILLS AND AROUND THE COLUMBIA RIVER GORGE EARLIER
TODAY. THESE CLOUDS AND FOG HAVE DEVELOPED UNDER INVERSIONS THAT RUN
FROM NEAR 3000 FEET MSL IN THE EAST TO NEAR 4000 FEET MSL NEAR THE
CASCADES. THERE IS A CLEAR ZONE OVER PORTIONS OF THE LOWER COLUMBIA
BASIN THAT IS EXPECTED TO MOSTLY FILL IN OVERNIGHT. MEANWHILE THE
NORTHERLY FLOW AND GRADIENTS OVER NORTH CENTRAL OREGON HAS BEEN
ALLOWING FOR A RAPID SOUTHWARD PLUNGE OF THE LOW CLOUDS AND FOG. AS
SUCH EXPECT THE LOW CLOUDS AND FOG TO MOVE INTO NORTHERN DESCHUTES
COUNTY BY MIDNIGHT. DUE TO THE HIGH ELEVATION OF THE INVERSION TOPS
THE THICKER FOG IS GENERALLY ABOVE 1700 FEET ALONG THE BLUE MOUNTAIN
FOOTHILLS AND ABOVE 2200 TO 2500 FEET OVER CENTRAL OREGON AND
CENTRAL WASHINGTON. UPDATES THIS EVENING HAVE BEEN TO ADJUST SKY
COVER AND FOG AREAS BASED ON CURRENT TRENDS. ALSO TEMPS SHOULD BE
SLOWER TO FALL WITHIN THE AREAS UNDER THE LOW CLOUDS AND FOG...AND
HAVE THEREFORE NUDGED SOME LOW TEMPS UP FOR TONIGHT. 90
.LONG TERM...PREVIOUS DISCUSSION...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.
&&
.AVIATION...06Z TAFS...STRONG LOW LEVEL INVERSIONS...WITH TOPS
RANGING FROM NEAR 3000 FT EAST SIDE TO NEAR 4000 FT WEST SIDE...
WILL CONTINUE OVER THE REGION DURING THIS PERIOD. THUS WIDESPREAD
MVFR OR LOWER CONDITIONS CAN BE EXPECTED AT ALL TAF SITES. LOCAL
LIFR AND VLIFR CONDITIONS ARE POSSIBLE AT ANY TIME...WITH KRDM A
PRIME CANDIDATE. SURFACE WINDS WILL REMAIN LESS THAN 10 KTS. 90
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 22 27 19 29 / 0 0 0 0
ALW 24 26 20 29 / 0 0 0 0
PSC 20 29 20 31 / 0 0 0 0
YKM 21 28 18 31 / 0 0 0 0
HRI 21 30 19 30 / 0 0 0 0
ELN 22 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 26 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
$$
90/94/90
