000
FXUS66 KPDT 201756 AAA
AFDPDT
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
953 AM PST THU NOV 20 2008
UPDATED AVIATION DISCUSSION
.UPDATE...REST OF TODAY AND THIS EVENING...HAVE INCREASED POPS AND
QPF IN MOST AREAS FOR TODAY AND FOR EASTERN AREAS THIS EVENING AS
SHARP NEGATIVE TILT TROUGH CROSSING CASCADES THIS MORNING PROVIDING
GOOD DYNAMICS. WITH SOUTHERLY FLOW AND STRONG LIFT EXPECT CASCADES
WILL HAVE LITTLE EFFECT ON PRECIPITATION PATTERN. REST OF FORECAST
OK AT THIS TIME.
.AVIATION...18Z TAFS...PATCHY DENSE FOG IS EXPECTED THROUGH 20Z AT
KPDT. ELSEWHERE...VISIBILITIES AND CEILINGS SHOULD HOVER AROUND
MVFR CONDITIONS THROUGH MUCH OF THE AFTERNOON AS A WEATHER SYSTEM
PRODUCES LIGHT RAIN ACROSS THE AREA. CEILINGS AND VISIBILITIES WILL
IMPROVE TO VFR TONIGHT BEHIND A COOL FRONT. EARLE
&&
.PREV DISCUSSION... /ISSUED 635 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...12Z TAFS...PATCHY DENSE FOG WILL BE AN ISSUE FOR
KPDT...AND KPSC. ALL OTHER TAF SITES MAY SEE TIMES OF MVFR TO IFR
CONDITIONS DUE TO LOW CIG`S AND/OR LOWERED VISIBILITIES...ACCEPT TAF
SITE KYKM IS EXPECTED TO STAY IN VFR CONDITIONS THROUGHOUT THE NEXT
24 HOURS. AN UPPER LEVEL DISTURBANCE IS PUSHING IN OFF THE WEST
COAST THIS MORNING. SHOWER ACTIVITY WILL PICK UP INTO THE DAYTIME
HOURS FOR ALL TAF SITES AS THIS SYSTEM MAKES ITS WAY ACROSS THE
AREA. WEBER
&&
.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 / 50 10 0 20
YKM 48 30 47 31 / 50 10 0 20
HRI 51 33 52 35 / 50 10 0 20
ELN 45 31 45 32 / 50 10 0 20
RDM 49 26 50 29 / 60 10 10 20
LGD 50 32 46 33 / 70 50 10 20
GCD 52 32 48 35 / 70 30 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
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