FXUS66 KPDT 260549 AAA
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
949 PM PST FRI DEC 25 2009
UPDATED SHORT TERM AND AVIATION DISCUSSIONS
.SHORT TERM...UPDATE...A HIGH AMPLITUDE UPPER RIDGE REMAINS ALONG
THE WEST COAST THIS EVENING. AS SUCH A FAIRLY STRONG INVERSION...
WITH A TOP NEAR 4500 FEET MSL...REMAINS OVER THE INTERIOR NORTHWEST.
MOISTURE REMAINS TRAPPED BELOW THIS INVERSION WITH STRATUS AND FOG
LINGERING OVER SOUTHEASTERN WASHINGTON AND PORTIONS OF NORTHEAST AND
CENTRAL OREGON. THE THICKEST FOG IS ROUGHLY FROM AROUND 2500 TO 3000
FEET MSL TO THE TOP OF THE INVERSION. HAVE UPDATED FORECASTS TO
BETTER REPRESENT THE DISTRIBUTION OF AREAS OF FOG VERSUS PATCHY FOG.
ALSO UPDATED TO NUDGE TEMPS UP IN AREAS UNDER THE LOWER LEVEL CLOUD
COVER. THE UPPER RIDGE WILL PINCH OFF AS IT IS UNDERCUT BY PACIFIC
ENERGY THAT IS DRIVING TOWARDS CALIFORNIA. AS THE HIGH PINCHES...A
PIECE OF THE ENERGY DRIVING OVER THE ROCKIES WILL SHEAR WEST OVER
THE PACIFIC NORTHWEST. THIS PIECE OF ENERGY FROM THE EAST WILL BE
DRY BUT MAY AFFECT THE INVERSIONS OVER THE INTERIOR NORTHWEST. SOME
CLEARING OF THE CLOUDS OVER KITTITAS AND NORTHWEST YAKIMA COUNTIES
MAY BE DUE TO THIS SYSTEM TRYING TO PUSH SLIGHTLY DRIER AIR INTO
THOSE AREAS. WILL SHOW LESS CLOUD COVER AND FOG...PLUS LOWER TEMPS
BACK...ACROSS THE CENTRAL WASHINGTON CASCADE EAST SLOPES DUE TO
CONTINUED DRYING THERE. 90
.LONG TERM...PREVIOUS DISCUSSION...MODELS HAVE THEIR DIFFERENCES FOR
THIS TIME PERIOD ESPECIALLY ON TIMING. HOWEVER IT APPEARS THAT A FEW
WEAK SYSTEMS WILL MOVE THROUGH THE REGION. THIS SHOULD BRING SOME
LIGHT PRECIPITATION AND MOSTLY CLOUDY SKIES. COLUMBIA BASIN STRATUS
AND FOG WILL LIKELY CONTINUE INTO MONDAY THEN DIMINISH ON TUESDAY.
TEMPERATURES WILL REMAIN A LITTLE BELOW NORMAL WITH LIGHT WINDS.
THURSDAY AND FRIDAY...NORTHWEST FLOW WILL CONTINUE THURSDAY WITH A
FEW UPSLOPE SHOWERS ALONG THE MOUNTAINS OF EASTERN OREGON AND THE
EAST SLOPES OF THE CASCADES. ANOTHER DISTURBANCE WILL MOVE IN LATE
THURSDAY EARLY FRIDAY AND WILL BRING A CHANCE FOR SNOW SHOWERS
CHANGING OVER TO RAIN SHOWERS. CURRENT MODELS INDICATE FAIRLY STRONG
WINDS AT THE 850MB LEVEL AND THAT WAA WITH THE APPROACHING SYSTEM
WILL ALLOW FOR THE COLD AIR TO MIX OUT OF THE LOWER ELEVATIONS.
HOWEVER...MODEL SOUNDINGS INDICATE THAT THERE MAY BE A SLIGHT CHANCE
OF FREEZING RAIN BEFORE THE WARM AIR PUSHES MIXES DOWN FRIDAY...BUT
TOO FAR IN THE EXTENDED TO ADD TO THE TEXT FORECAST.
&&
.AVIATION...06Z TAFS...A STRONG LOW LEVEL INVERSION WILL KEEP MVFR
OR LOWER CONDITIONS GOING AT KRDM...KPDT AND KALW THROUGH THE NEXT
24 HOURS. KDLS...KYKM AND KPSC SHOULD SEE EITHER LOW VFR OR MVFR
CONDITIONS. THE WILD CARD FOR KYKM AND KPSC (TO A LESSER EXTENT
KDLS) IS SOME DRIER AIR TRYING TO INTRUDE FROM THE NORTHWEST. IF
THIS MAKES IT INTO THESE SITES COULD SEE CLEARING OF THE CURRENT
STRATUS WHICH IN TURN COULD LEAD TO MUCH LOWER CIGS/VIS. FOR NOW
WILL SHOW THIS POSSIBILITY AT KPSC AND KYKM...BUT CONFIDENCE HAS
BECOME LOW AS TO POTENTIAL TRENDS AT THESE TWO SITES. SURFACE WINDS
WILL BE LESS THAN 10 KTS. 90
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 23 29 17 30 / 0 0 0 0
ALW 25 28 19 30 / 0 0 0 0
PSC 23 32 19 31 / 0 0 0 0
YKM 23 31 16 29 / 0 0 0 0
HRI 24 31 17 30 / 0 0 0 0
ELN 19 29 18 31 / 0 0 0 0
RDM 17 27 20 31 / 0 0 10 10
LGD 15 25 16 29 / 0 0 0 0
GCD 17 36 16 34 / 0 0 10 10
DLS 29 34 21 33 / 0 0 10 0
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL 4 PM PST SATURDAY FOR ORZ041>044-
049-501-504-505.
WA...AIR STAGNATION ADVISORY UNTIL 4 PM PST SATURDAY FOR WAZ024-
026>029-501-502.
&&
THREAT INDEX
SATURDAY : GREEN
SUNDAY : GREEN
MONDAY : 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
$$
90/94/90
