000
FXUS66 KPDT 032357 AAA
AFDPDT
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
357 PM PST WED DEC 3 2008
UPDATED AVIATION DISCUSSION.
.SHORT TERM...TONIGHT THROUGH SATURDAY...ABUNDANT MOISTURE WITH A
FAVORED NORTHERLY UPSLOPE FLOW WILL KEEP POTENTIAL SHOWERS ACROSS
THE FAR NORTHEAST MOUNTAINS THROUGH THE OVERNIGHT HOURS. DON`T
EXPECT ANY SIGNIFICANT SNOW ACCUMULATIONS HOWEVER. OTHERWISE...
EXPECT SKIES TO GRADUALLY CLEAR HEADING INTO TOMORROW MORNING. FOG
MAY FORM NEAR RIVERS ACROSS THE LOWER COLUMBIA BASIN, BUT EXPECT IT
WILL BE PATCHY AS BEST WITH SOME FORM OF CLOUD COVER PERSISTING
UNTIL AROUND SUNRISE. ANY THAT DOES FORM WILL BE SLOW TO BURN OFF
GIVEN THE LOW SUN ANGLES THIS TIME OF YEAR IN ADDITION TO RELATIVELY
LIGHT SURFACE WINDS.
HIGH PRESSURE WILL CONTINUE TO SLOWLY BUILD OVER THE REGION THROUGH
MOST OF FRIDAY. DID NOT INCLUDE FOG AFTER TOMORROW AS NORTHERLY LOW
LEVEL FLOW WILL LIKELY FUNNEL A DRIER CONTINENTAL AIR MASS AND
PRECLUDE DEVELOPMENT. A SUBSIDENCE INVERSION WILL KEEP DAYTIME
TEMPERATURES ON THURSDAY SOMEWHAT LOWER THAN EXPECTED...ESPECIALLY
ACROSS THE COLUMBIA BASIN AND LARGER VALLEYS...GIVEN THE AMPLE
SUNSHINE. IN ADDITION...CLOUDS MOVING THROUGH THE UPPER FLOW WILL
LIMIT HEATING SOMEWHAT ON FRIDAY.
FRIDAY NIGHT AND SATURDAY REMAINED THE MOST SIGNIFICANT CHALLENGE
FOR THIS FORECAST AS A DIVERGENCE IN 12Z MODEL SOLUTIONS BECAME
APPARENT. THE NAM SHOWED A WAVE FLATTENING THE RIDGE AND ACTUALLY
BRINGING WARM PROCESS PRECIPITATION ACROSS THE NORTHEASTERN 2/3RDS
OF THE FORECAST AREA VERY LATE FRIDAY NIGHT AND MAINLY ON SATURDAY.
THE GFS AND THE ECMWF RETAINED THE STRENGTH OF THE RIDGE AND KEPT
THE WAVE NORTH ACROSS NORTHERN WASHINGTON AND SOUTHERN BRITISH
COLUMBIA. THE SREF AND GFS ENSEMBLES PROVIDED NON-TRIVIAL SUPPORT TO
THE NAM SO DECIDED TO CONTINUE CURRENT FORECAST THOUGHTS OF LOW END
POPS. ASSUMING THE NAM COMES TRUE, WOULD THEN HAVE SIGNIFICANT
CONCERN ABOUT COLD AIR BEING TRAPPED RESULTING IN SOME FORM OF
FREEZING PRECIPITATION POTENTIAL FOR THE COLUMBIA BASIN AND
ADJOINING VALLEYS. CONFIDENCE WAS FAR TOO LOW IN THIS SCENARIO, SO
DECIDED TO ASSUME THE TRAPPING WOULD NOT OCCUR AND MAINTAIN THE LOW
POPS ALONG WITH LOW QPF AMOUNTS. 18Z RUN OF THE NAM HAS BACKED OFF
ON BREAKING THE RIDGE DOWN, SO WOULD NOT BE SURPRISED IF FOLLOWING
SHIFTS REMOVE POPS ALTOGETHER. /JBONK
.LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY...MODELS ARE IN GOOD
AGREEMENT IN BRINGING A FRONTAL SYSTEM INTO THE AREA SATURDAY NIGHT
AND SUNDAY WITH A CHANCE OF RAIN TO MOST OF THE AREA. SNOW LEVELS
ARE GENERALLY ABOVE 5000 FEET SO SNOW SHOULD BE CONFINED TO THE
MOUNTAINS. RIDGING BUILDS OVER THE AREA SUNDAY NIGHT THROUGH MONDAY
NIGHT ALTHOUGH MODELS DIFFER TO THE STRENGTH OF THE RIDGE. A MOIST
NORTHWEST FLOW OVER THE RIDGE WILL KEEP A CHANCE OF RAIN IN THE
MOUNTAINS. WITH THE RIDGE IN PLACE AM ANTICIPATING A RETURN OF
COLUMBIA BASIN FOG AND COOL TEMPERATURES IN THE LOWER 40S DURING THE
DAY AND MID 30S AT NIGHT. THE REST OF THE AREA WILL SEE NEAR NORMAL
VALUES. LATE MONDAY NIGHT AND TUESDAY WILL SEE ANOTHER FRONTAL
SYSTEM MOVE THROUGH THE AREA WITH A CHANCE OF RAIN AND SNOW ABOVE
4500 FEET AND WARMER NEAR NORMAL TEMPERATURES. THE RIDGE WILL
REBUILD TUESDAY NIGHT AND WEDNESDAY WITH CONTINUED SHOWERS IN THE
MOUNTAINS DUE TO THE NORTHWEST FLOW. PERRY
&&
.AVIATION DISCUSSION...00Z TAFS...A STRATUS DECK AROUND 5000 FT AGL
WILL CONTINUE OVER THE COLUMBIA BASIN AND ADJACENT VALLEYS THIS
EVENING WITH BROKEN HIGH LEVEL CLOUDS ABOVE 12000 FT AGL OVER THE
REST OF THE AREA. LATER THIS EVENING THE STRATUS DECK WILL LOWER TO
AROUND 2500 FT AGL OVER KDLS...KALW...KPDT AND POSSIBLY KPSC. PATCHY
FOG WITH IFR CEILINGS AND MVFR VISIBILITIES IS POSSIBLE AFTER 10Z IN
THOSE LOCATIONS. SKIES WILL GENERALLY LIFT TO ABOVE 5000 FT AGL AND
PARTIALLY CLEAR AFTER 18Z TOMORROW MORNING. SURFACE WINDS WILL BE
UNDER 10 KTS. PERRY
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 29 37 24 42 / 10 0 0 10
ALW 29 36 26 40 / 10 0 0 10
PSC 22 37 24 40 / 10 0 0 10
YKM 23 41 22 43 / 0 0 0 10
HRI 23 38 22 42 / 10 0 0 10
ELN 26 40 23 44 / 0 0 0 10
RDM 25 43 20 49 / 0 0 0 0
LGD 29 40 26 44 / 20 0 0 10
GCD 34 43 27 47 / 10 0 0 0
DLS 33 44 26 44 / 0 0 0 10
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&
$$
TI:GGG
FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON
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