000
FXUS66 KPDT 201042
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
240 AM PST THU NOV 20 2008
.SHORT TERM...TODAY THROUGH FRIDAY NIGHT...AN UPPER HIGH PRESSURE
RIDGE WILL BREAK DOWN TODAY AND MOVE EAST ENABLING THE FLOW TO TURN
TO THE SOUTHWEST AS AN UPPER TROUGH OFF THE COAST MOVES CLOSER TO
THE COAST. THERE WILL BE A WEAK WAVE IN THE FLOW WHICH WILL MOVE
ACROSS THE FORECAST AREA THIS MORNING WITH A LITTLE MOISTURE. THEN
MORE SIGNIFICANT MOISTURE WILL MOVE IN BEHIND IT THIS AFTERNOON AND
TONIGHT AS A SECONDARY UPPER TROUGH TAKES ON A NEGATIVE TILT AS IT
MOVES INLAND. THERE WILL BE A FAIRLY SIGNIFICANT SLUG OF MOISTURE
WITH THIS SECOND TROUGH CAUSING ALL AREAS TO LIKELY SEE AT LEAST
SOME RAINFALL...WITH SNOW ONLY IN THE HIGHER MOUNTAINS MAINLY
TONIGHT. WITH SNOW LEVELS BEING FAIRLY HIGH WILL NOT NEED TO BE
CONCERNED ABOUT SNOW ADVISORY SNOW ACCUMULATIONS. THIS WEATHER
SYSTEM WILL ENABLE BETTER MIXING OF THE LOWER ATMOSPHERE TO ALLOW
TRAPPED POLLUTANTS TO ESCAPE THE VALLEYS. WILL LIKELY BE ABLE TO END
THE AIR STAGNATION ADVISORY LATER THIS MORNING AS A RESULT. WEAK
HIGH PRESSURE AND DRY CONDITIONS WILL RETURN BEHIND THIS SYSTEM BY
FRIDAY MORNING. THE PRECIPITATION WILL DECREASE FROM WEST TO EAST
LATE TONIGHT AND FRIDAY. ANOTHER WEATHER DISTURBANCE...THOUGH
WEAK...WILL MOVE ACROSS THE PACIFIC NORTHWEST AGAIN FRIDAY NIGHT
THROUGH SATURDAY MORNING. THERE WILL BE MUCH LESS MOISTURE WITH THIS
NEXT SYSTEM AND PRECIPITATION WILL MAINLY BE IN THE MOUNTAINS...
HOWEVER THERE COULD BE SOME LIGHT SHOWERS IN THE LOWER ELEVATIONS AS
WELL. 88
.LONG TERM...SATURDAY THROUGH WEDNESDAY NIGHT...MODELS ARE IN GOOD
AGREEMENT FOR THE FORECAST PERIOD. A WEAK UPPER LEVEL DISTURBANCE
WILL PUSH OUT OF THE AREA SATURDAY NIGHT. SHOWER ACTIVITY WILL
DIMINISH EXCEPT FOR SOME LINGERING SHOWERS OVER THE EAST SLOPES OF
THE WASHINGTON CASCADES AND THE BLUE MOUNTAINS ON SUNDAY MORNING. AN
UPPER LEVEL RIDGE WILL PROVIDE DRY CONDITIONS FOR THE AREA...BUT FOG
IS A CONCERN AS WELL DUE TO THE MOISTURE FROM THE PREVIOUS SYSTEMS.
AS HIGH PRESSURE EXIT THE AREA MONDAY NIGHT BOTH ECMWF AND GFS
SUGGEST A CLOSED LOW OFF THE SOUTHERN CALIFORNIA COAST ACCOMPANIED
BY A MODERATE TROUGHING PATTERN OVER BRITISH COLUMBIA. THE QUESTION
REMAINS IF THIS SYSTEM WILL FOLLOW THIS PATTERN...OR IF IT WILL BE A
MORE AMPLIFIED TROUGH. RIGHT NOW SHOWER ACTIVITY LOOKS TO BE MAINLY
IN THE MOUNTAINS AS THE CURRENT TROUGH PATTERN HAS MORE OF AN IMPACT
TO THE NORTH IN SPOKANE. THE REST OF THE AREA WOULD BE UNDER SPLIT
FLOW BETWEEN THE TWO SYSTEMS. IF THE TWO SYSTEMS MERGE AS ONE IN
FUTURE MODEL RUNS IT IS MORE LIKELY THAT WE WILL SEE ACTIVE WEATHER
TUESDAY AND INTO WEDNESDAY. WEBER
&&
.AVIATION...06Z TAFS...A WEAK DISTURBANCE MOVING THROUGH THE AREA
ALONG WITH SOUTHERLY WINDS HAVE GIVEN THE AREA SOME BRIEF RELIEF
FROM THE LOW CLOUDS AND FOG OVER COLUMBIA BASIN. THE FOG SHOULD
RETURN LATER TONIGHT AND VISIBILITY IS ALREADY DROPPING IN A FEW
PLACES. DO NOT EXPECT IT TO BE AS DENSE OR WIDESPREAD. MVFR/IFR
CEILINGS AND VISIBILITY ARE POSSIBLE AT ALL TAF LOCATIONS...BUT
ESPECIALLY AT KPDT AND KALW. THE FOG SHOULD LIFT IN THE LATE
MORNING AS A FRONT MOVES INTO THE AREA WITH RAIN AND OCCASIONAL
MVFR CEILINGS. WINDS WILL BE UNDER 10 KTS THROUGH EARLY TOMORROW
AFTERNOON. THE FRONT WILL THEN BRING WINDS OF 10 TO 20 KTS WITH
GUSTS TO 25 KTS THROUGH TOMORROW EVENING. PERRY
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 51 36 50 39 / 60 20 0 20
ALW 52 37 51 39 / 60 20 10 20
PSC 51 34 51 36 / 40 10 0 20
YKM 48 30 47 31 / 50 10 0 20
HRI 51 33 52 35 / 40 10 0 20
ELN 45 31 45 32 / 50 10 0 20
RDM 49 26 50 29 / 40 10 10 20
LGD 50 32 46 33 / 70 40 10 20
GCD 52 32 48 35 / 70 20 10 20
DLS 51 36 52 40 / 50 10 0 30
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL NOON PST TODAY FOR ORZ041-044-501.
WA...AIR STAGNATION ADVISORY UNTIL NOON PST TODAY FOR WAZ024-026>029.
&&
$$
TI:GGG
FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON
88/89/89
