FXUS66 KPDT 301723
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
920 AM PST MON NOV 30 2009
.UPDATE...A WEAKENING FRONT IS SAGGING SOUTH OUT OF THE GULF OF
ALASKA THIS MORNING AND IS APPROACHING THE OLYMPIC PENINSULA THIS
MORNING. THE FRONT IS FLATTENING THE RIDGE OVER THE AREA AND SENDING
MID AND HIGH LEVEL CLOUDS INTO THE WASHINGTON CASCADES. HAVE BEEFED
UP CLOUD COVER FOR THE APPROACHING FRONT TODAY...TONIGHT AND TUESDAY
MORNING. PATCHY FOG AND FREEZING FOG REMAINS IN PORTIONS THE YAKIMA
AND KITTITAS VALLEYS...THE LOWER COLUMBIA BASIN AND WALLOWA COUNTY.
HAVE ISSUED NOWCASTS TO COVER THE SITUATION. EXPECT THAT THE FOG
WILL LIFT BY THIS AFTERNOON BUT HAVE LOWERED TEMPERATURES A FEW
DEGREES TODAY IN THE FOG AFFECTED AREAS. WINDS HAVE BEEN STRONGER
THAN FORECAST IN THE GRANDE RONDE VALLEY SO HAVE BUMPED THEM UP TO
20 TO 30 MPH TODAY AND 10 TO 20 MPH TONIGHT. LADD CANYON HAS BEEN
APPROACHING WIND ADVISORY LEVELS AT TIMES AND FURTHER STRENGTHENING
MAY REQUIRE A WIND ADVISORY BUT WILL HOLD OFF FOR NOW. CURRENT
FORECAST HAS WINDS STRENGTHENING IN THE KITTITAS VALLEY THIS
AFTERNOON AND THAT LOOKS PROBABLE AS THE FRONT APPROACHES. WILL
ISSUE A FORECAST UPDATE SHORTLY. PERRY
.AVIATION...18Z TAFS. LIFR CONDITIONS AT PSC DLS WILL CONTINUE FOR A
FEW MORE HOURS AS AREAS OF FOG ARE LIMITING VISIBILITY IN THE
COLUMBIA BASIN AND ADJACENT VALLEYS. OTHERWISE VFR CONDITIONS TODAY
WITH HIGH LEVEL CLOUDS AND CEILINGS 150-250. SURFACE WINDS 5-10 KT.
A WEAK COLD FRONT WILL MOVE THROUGH TONIGHT WITH LOWER CEILINGS AT
040-060. SURFACE WINDS 5-15 KT. 94
&&
.PREV DISCUSSION... /ISSUED 755 AM PST MON NOV 30 2009/
SHORT TERM...MONDAY THROUGH WEDNESDAY...A FLAT RIDGE WILL REMAIN
OVER THE PACIFIC NORTHWEST TODAY. PATCHY FOG HAS DEVELOPED IN THE
YAKIMA VALLEY..AND MAY DEVELOP IN OTHER LOCATIONS IN THE COLUMBIA
BASIN THIS MORNING...PARTICULARLY NEAR THE RIVERS. A WEAKENING FRONT
WILL MOVE THROUGH THE RIDGE TONIGHT...BUT IS TOO DRY TO HAVE MUCH
IMPACT. THE DRIER COLDER AIR MASS BEHIND THE FRONT SHOULD HELP
WEAKEN AND MIX OUT THE SURFACE INVERSIONS THAT HAVE ALLOWED PATCHY
FOG TO DEVELOP AT NIGHT. THE UPPER LEVEL RIDGE WILL REBUILD OFFSHORE
TUESDAY AND WEDNESDAY WITH DRY NORTHERLY FLOW OVER EASTERN
WASHINGTON AND OREGON. THE MAIN CHANGES IN THE FORECAST WERE IN SKY
COVER. VERY LITTLE CLOUD COVER CURRENTLY OVER THE AREA SO REDUCED
CLOUDS FOR TODAY...INCREASED IT WITH THE APPROACHING FRONT THIS
AFTERNOON AND OVERNIGHT...THEN DECREASED CLOUDS AGAIN TUESDAY AND
WEDNESDAY WITH THE DRIER AIR MOVING IN BEHIND THE FRONT. COONFIELD
LONG TERM...WEDNESDAY NIGH THROUGH MONDAY...MODELS CONTINUE TO SHOW
SIGNIFICANT DIFFERENCES IN THE LONG TERM AND CONTINUE TO CHANGE
THEIR SOLUTIONS FROM RUN TO RUN. CONFIDENCE IS NOT HIGH AND HAVE
TRIED TO MAINTAIN A MIDDLE GROUND BETWEEN THE VARIOUS SOLUTIONS.
INITIALLY A STRONG RIDGE WILL BE CENTERED OVER THE WEST COAST FOR
FAIR AND DRY CONDITIONS. GIVEN INCREASING HIGH CLOUDS AND A LACK OF
SIGNIFICANT LOW LEVEL MOISTURE...HAVE CHOSEN TO REMOVE FOG FROM
THURSDAY MORNINGS FORECAST. HOWEVER...SMALL AREAS OF PATCHY FOG
COULD STILL BE POSSIBLE IN AND AROUND THE RIVER VALLEYS OF THE
COLUMBIA BASIN SINCE WINDS WILL BE LIGHT. A TROUGH IS THEN EXPECTED
TO SWING THROUGH NORTHERN PORTIONS OF THE AREA LATE THURSDAY OR
THURSDAY NIGHT. THIS DISTURBANCE COULD BRING RAIN OR SNOW SHOWERS TO
THE EASTERN SLOPES OF THE CASCADES...AND THEN TO THE MOUNTAINS OF
NORTHEAST OREGON AND SOUTHEAST WASHINGTON BY FRIDAY. FROM FRIDAY
NIGHT ONWARD THERE ARE TOO MANY MODEL DIFFERENCES TO DETERMINE WHEN
AND HOW MUCH PRECIPITATION WILL FALL OVER THE WEEKEND AND INTO NEXT
WEEK. HOWEVER...THE GENERAL CONSENSUS IS THAT LARGE SCALE TROUGHING
WILL DEVELOP OVER THE PACIFIC NORTHWEST...USHERING IN MUCH COLDER
AIR. IT IS NOT YET CERTAIN HOW COLD IT WILL BE ON SUNDAY AND
MONDAY...BUT IT IS A FAIR BET THAT ANY PRECIPITATION THAT DOES FALL
WILL BE IN THE FORM OF SNOW...ESPECIALLY ON MONDAY. 82
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 47 34 44 24 / 0 10 10 0
ALW 47 35 39 28 / 0 10 10 0
PSC 43 31 43 25 / 0 10 0 0
YKM 45 29 45 25 / 0 0 0 0
HRI 43 30 45 22 / 0 10 10 0
ELN 46 32 43 23 / 0 10 0 0
RDM 51 20 46 20 / 0 0 0 0
LGD 42 28 42 22 / 0 10 10 0
GCD 46 28 44 26 / 0 0 10 0
DLS 47 35 47 33 / 0 0 0 0
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&
THREAT INDEX
TODAY : GREEN
TUESDAY : GREEN
WEDNESDAY : 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
$$
99/94
