FXUS66 KPDT 240543 AAA
AFDPDT
AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE PENDLETON OR
943 PM PST WED DEC 23 2009
UPDATED AVIATION DISCUSSION
.SHORT TERM...UPDATE...THE UPPER RIDGE ALONG WEST COAST WILL
CONTINUE TO BUILD THROUGH TONIGHT. THIS WILL KEEP THE REGION UNDER A
NORTH-NORTHWEST FLOW ALOFT. WILL CONTINUE TO SEE VARIABLE AMOUNTS OF
HIGH CLOUDINESS...WHICH SHOULD HELP SLOW ANY FOG DEVELOPMENT
TONIGHT. OVERALL INVERSIONS LOOK TO BE MINIMAL TONIGHT. THERE IS A
VERY WEAK INVERSION AROUND 3000 TO 3500 FEET OVER THE BASIN...BUT
THIS LOOKS TO FURTHER WEAKEN OVERNIGHT. RADIATIVE COOLING SHOULD
ALLOW FOR SOME SHALLOW LOW ELEVATION INVERSIONS TO FORM LATE IN THE
TONIGHT PERIOD...MAINLY TOWARDS DAYBREAK. THESE MAY BE ABLE TO TRAP
ENOUGH MOISTURE FOR FOG...MAINLY NEAR THE COLUMBIA RIVER AND IN THE
UPPER YAKIMA VALLEY. HAVE TWEAKED FORECASTS TO ACCOMMODATE THIS FOG
POSSIBILITY...THOUGH MAY WIND UP WITH TOO MUCH FROST OUT FOR ANY
FOG. THERE IS A PATCH LOW CLOUDS AND/OR FOG OVER GILLIAM COUNTY IN
NORTH CENTRAL OREGON AT THE MOMENT. AM UNSURE OF HOW THIS AREA WILL
PLAY OUT...BUT WILL FOR NOW GO WITH THE IDEA THAT ADVECTION OF DRIER
AIR LATER TONIGHT WILL CAUSE IT TO DISSIPATE (COULD JUST AS EASILY
SPREAD OUT IN ALL DIRECTIONS FROM THIS LOCATION OVERNIGHT). TEMPS
AND DEW POINTS HAVE NOT BEEN FALLING QUITE AS QUICKLY AS EXPECTED...
BUT COULD EASILY GET BACK ON TRACK. DID NUDGE A FEW TEMPS UP
THOUGH...PARTICULARLY IN THE YAKIMA AND KITTITAS VALLEYS AND NEAR
CLE ELUM. 90
.LONG TERM...PREVIOUS DISCUSSION...AN UPPER LEVEL RIDGE CONTINUES TO
LINGER OVER THE PACIFIC NORTHWEST. AREAS OF FREEZING FOG WILL
CONTINUE IN THE LOWER ELEVATIONS THROUGH MONDAY. CONDITIONS
ELSEWHERE WILL REMAIN COOL AND DRY. FORECAST BEYOND MONDAY WILL BE A
BIT TRICKY AS ECMWF AND GFS BOTH INDICATE A BREAKDOWN OF THE RIDGE
WITH THE NEXT SYSTEM. HOWEVER...QPF AMOUNTS AND PLACEMENT OF THE THE
PRECIPITATION IS STILL QUESTIONABLE. THE SYSTEM WILL CUT OFF THE
UPPER LEVEL RIDGE AND PROVIDE A GOOD SWATH OF MOISTURE TO THE
SOUTHWESTERN CONUS. ECMWF HAS A DEFORMATION ZONE OVER EASTERN
OREGON...BUT PRECIPITATION AMOUNTS FROM MONDAY MORNING TILL TUESDAY
EVENING ARE STILL FAIRLY WEAK. GFS HAS A WEAK LOW PRESSURE SYSTEM
RETROGRADING OVER THE SPOKANE AREA BY TUESDAY MORNING PULLING
MOISTURE IN FROM THE NORTHWEST. THIS PARTICULAR PATTERN USUALLY ENDS
UP WITH A RAINSHADOW EFFECT OFF THE CASCADES...KEEPING AREAS ALONG
THE EAST SLOPES WITH SLIGHT CHANCE SHOWERS...AND THE LOWER
ELEVATIONS DRY. UPSLOPE FLOW WILL ALLOW FOR SHOWERS TO REDEVELOP
ALONG THE FOOTHILLS OF THE BLUE MOUNTAINS AND PROGRESS EASTWARD.
AGAIN QPF AMOUNTS ARE STILL FAIRLY WEAK...AND DO NOT APPEAR TO BE OF
ANY THREAT FOR THE TIME BEING. MODELS HAVE BEEN BACK AND FORTH THE
PAST SEVERAL DAYS AS TO WHAT WILL HAPPEN IN THE EXTENDED...THEREFORE
FORECAST CONFIDENCE IS LOW.
&&
.AVIATION...06Z TAFS...VFR CONDITIONS ARE GENERALLY EXPECTED OVER
THE NEXT 24 HOURS AT ALL TAF SITES. WEAK INVERSIONS AT LOW
ELEVATIONS ARE EXPECTED TO DEVELOP LATER TONIGHT...TOWARDS DAYBREAK.
THESE INVERSIONS WILL MAINLY AFFECT SITES NEAR THE COLUMBIA RIVER
AND IN THE UPPER YAKIMA BASIN. THERE IS A SLIGHT DRYING TREND
INDICATED BY REGIONAL OBSERVATIONS AND SOME THIN HIGH CLOUDINESS
THAT MAY HAMPER INVERSION DEVELOPMENT. STILL WILL INDICATE SOME
LOWER VIS AND/OR CIGS AT KDLS AND KPSC BETWEEN 12 AND 18 UTC. FOR
KYKM...A LITTLE MIST IS CURRENTLY OCCURRING AND WILL INDICATE A SLOW
DEGRADATION THROUGH DAYBREAK. ELSEWHERE EXPECT ELEVATIONS ABOVE LOW
LEVEL INVERSIONS AND FROST OUT TO CURTAIL MOST FOG THREATS...THOUGH
SOME LIGHT MIST MAY ADVECT TO NEAR KALW LATE THURSDAY MORNING. 90
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 19 27 17 27 / 0 0 0 0
ALW 20 27 19 26 / 0 0 0 0
PSC 18 28 18 29 / 0 0 0 0
YKM 18 29 15 28 / 0 0 0 0
HRI 17 29 17 29 / 0 0 0 0
ELN 19 29 15 27 / 0 0 0 0
RDM 13 37 13 37 / 0 0 0 0
LGD 12 27 11 31 / 0 0 0 0
GCD 15 33 17 36 / 0 0 0 0
DLS 23 34 20 32 / 0 0 0 0
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY FROM 4 AM THURSDAY TO 4 PM PST SATURDAY
FOR ORZ041>044-049-501-504-505.
WA...AIR STAGNATION ADVISORY FROM 4 AM THURSDAY TO 4 PM PST SATURDAY
FOR WAZ024-026>029-501-502.
&&
THREAT INDEX
THURSDAY : GREEN
FRIDAY : GREEN
SATURDAY : 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
$$
90/89/90
