FXUS66 KPDT 262230
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
230 PM PST SAT DEC 26 2009
.SHORT TERM...TONIGHT THROUGH MONDAY NIGHT...IMMEDIATE SHORT TERM
CONCERN IS THE STABLE CONDITIONS AND STAGNANT AIR MASS CONTINUING IN
THE FORECAST AREA. A HIGHLY AMPLIFIED LONG WAVE PATTERN IN THE
MID/UPPER LEVELS ACROSS THE NORTHERN PACIFIC OCEAN AND NORTH AMERICA
WILL KEEP HIGH PRESSURE OVER THE REGION THROUGH MONDAY NIGHT. THIS
PATTERN WILL ALLOW A PERSISTENT TEMPERATURE INVERSION BELOW 10000
FEET TO PRODUCE A STAGNANT... SUBFREEZING AIR MASS WITH VERY LIGHT
OR CALM WINDS IN THE BOUNDARY LAYER...WHICH WILL TRAP MOISTURE
RESULTING IN EXTENSIVE LOW STRATUS CLOUD DECK AND PATCHY FREEZING IN
THE LOWER COLUMBIA BASIN AND ADJACENT VALLEYS AS WELL AS ALONG THE
FOOTHILLS OF THE BLUE MOUNTAINS AND IN NORTH CENTRAL OREGON THROUGH
THE PERIOD. THE AIR STAGNANT ADVISORY HAS BEEN EXTENDED IN TIME AND
IS NOW IN EFFECT UNTIL 4 PM PST MONDAY. FOR ADDITIONAL INFORMATION
CONCERNING THE AIR STAGNATION ADVISORY SEE PRODUCT PDXNPWPDT. POLAN
.LONG TERM...TUESDAY THROUGH THURSDAY NIGHT...MODELS ARE IN FAIRLY
GOOD AGREEMENT IN BRINGING A FRONT TO THE PACIFIC NORTHWEST COAST ON
TUESDAY. THIS WILL BRING A WESTERLY FLOW TO THE AREA AND A SLIGHT
CHANCE OF SNOW TO THE EAST SLOPES OF THE CASCADES AND THE EASTERN
MOUNTAINS AND PERHAPS CENTRAL OREGON IN THE LATE AFTERNOON. AREAS
BELOW 3000 FEET WILL CONTINUE TO HAVE LOW STRATUS AND PATCHY FOG AND
FREEZING FOG. TEMPERATURES WILL REMAIN IN THE UPPER 20S TO MID 30S.
THE FRONT WILL MOVE THROUGH THE AREA TUESDAY NIGHT AND WEDNESDAY AND
THOUGH MODELS DISAGREE SOMEWHAT ON THE STRENGTH AND TIMING...
PRECIPITATION AMOUNTS DO NOT LOOK VERY SUBSTANTIAL. FOR NOW WILL
FORECAST THE LOW STRATUS AND FOG TO BE SCOURED OUT OF THE LOWER
ELEVATIONS BUT AM NOT VERY CONFIDENT THE FRONT WILL BE STRONG ENOUGH
TO DO THAT. THE ECMWF BRINGS IN A FAIRLY STRONG SYSTEM WITH GOOD
MOISTURE THURSDAY AND THURSDAY NIGHT MAINLY IN THE SOUTHERN HALF OF
THE AREA. THE GFS BRINGS IN A WEAKER SYSTEM ON THURSDAY NIGHT WITH
MOST OF THE ENERGY IN THE NORTH. HAVE LEANED TOWARDS THE GFS AND
GIVEN THE ENTIRE AREA A CHANCE OF SNOW ON THURSDAY NIGHT.
TEMPERATURES WILL CONTINUE IN THE UPPER 20S TO MID 30S IN THE DAY
AND IN THE UPPER TEENS TO UPPER 20S AT NIGHTS. PERRY
FRIDAY AND SATURDAY...MODELS CONTINUE TO INDICATE A BREAK DOWN OF
THE RIDGE WITH THE NEXT APPROACHING SYSTEM. STRONG 850 WINDS AND WAA
ADVECTION ASSOCIATED SHOULD RAISE SNOW LEVELS NEAR THE CASCADE CREST
FRIDAY AFTERNOON. SHOWER ACTIVITY SHOULD BE MAINLY IN THE FORM OF
RAIN. THE BETTER CHANCE FOR SHOWERS WILL BE ALONG THE EAST SLOPES OF
THE CASCADES AND AND THE MOUNTAINS OF NORTHEAST OREGON. ELSEWHERE
WILL HAVE A CHANCE FOR RAIN SHOWERS. THERE IS STILL A CHANCE IF THE
WINDS DO NOT MIX THE WARM AIR DOWN THAT THIS COULD BE ANOTHER
CLASSIC FREEZING RAIN SITUATION. WILL MONITOR THE SYSTEM EACH DAY
AND MAKE ADJUSTMENTS ACCORDINGLY. WEBER
&&
.PREVIOUS AVIATION DISCUSSION...18Z TAFS...A STRONG LOW LEVEL
INVERSION WILL WEAKEN SOMEWHAT TODAY DUE TO A PASSING WEAK
DISTURBANCE BUT WILL RESTRENGTHEN TONIGHT. MVFR AND IFR CONDITIONS
WILL CONTINUE THROUGH TOMORROW MORNING AT KALW...KPSC...KPDT AND
KRDM. KYKM AND KDLS WILL HAVE VFR CONDITIONS THROUGH THIS AFTERNOON
THEN WILL DROP TO MVFR LEVELS THROUGH TOMORROW MORNING. SURFACE
WINDS WILL CONTINUE TO BE UNDER 10 KTS. PERRY
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 20 29 19 30 / 0 0 10 0
ALW 23 29 21 30 / 0 0 0 0
PSC 21 30 19 30 / 0 0 0 0
YKM 18 30 17 30 / 0 0 0 0
HRI 19 30 17 30 / 0 0 10 0
ELN 16 31 17 30 / 0 0 0 0
RDM 19 36 18 37 / 10 30 30 20
LGD 15 29 19 31 / 0 0 0 0
GCD 15 34 20 35 / 10 20 20 20
DLS 24 33 23 34 / 10 10 20 10
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL 4 PM PST MONDAY FOR
ORZ041>044-049-501-504-505.
WA...AIR STAGNATION ADVISORY UNTIL 4 PM PST MONDAY FOR
WAZ024-026>029-501-502.
&&
THREAT INDEX
SUNDAY : GREEN
MONDAY : GREEN
TUESDAY : 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
$$
99/83/83
