FXUS66 KPQR 231628
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
830 AM PST WED DEC 23 2009
.SYNOPSIS...COOL DRY OFFSHORE FLOW FOR REST OF THE WEEK...AS STORMS
HOLD UP OVER THE N PAC. WILL SEE FOGGY WEATHER IN THE CENTRAL AND
SOUTH WILLAMETTE VALLEY NEXT SEVERAL DAYS...BUT EAST WINDS WILL KEEP
OTHER AREAS PARTLY TO MOSTLY SUNNY.
&&
.SHORT TERM...PLENTY OF FOG ACROSS THE REGION THIS MORNING...WITH
AREAS OF DENSE FOG STILL REPORTED ACROSS MUCH OF THE INTERIOR. WILL
EXTEND DENSE FOG ADVISORY UNTIL 11 AM.
THE RIDGE ALOFT WILL CONTINUE TO STRENGTHEN AND SHARPEN A BIT
TOMORROW THEN SHIFT EAST SO THAT ITS AXIS ALONG THE COAST BY THU AM.
IN RESPONSE OFFSHORE FLOW WILL DEVELOP WITH EAST WINDS STRENGTHENING
THROUGH THE COLUMBIA RIVER GORGE AND OTHER GAPS AND PASSES IN THE
CASCADES. EAST WINDS WILL INCREASE GRADUALLY TODAY...REACHING THE 15
TO 20 KT RANGE IN THE W GORGE. WINDS WILL PICK UP MORE RAPIDLY
TONIGHT AND THU AS A STRONG OFFSHORE PRES GRADIENT SETS UP ALONG
THE CASCADES. SUSTAINED WINDS WILL LIKELY PEAK OUT AROUND 40 OR 45
KNOTS WITH GUSTS TO 50 OR 60 KNOTS IN THE WINDIEST LOCATIONS SUCH AS
ROOSTER ROCK. EAST WINDS WILL DIMINISH THIS WEEKEND.
ASIDE FROM THE INCREASING GAP WINDS...FOG IN THE WIND SHELTERED
VALLEYS INCLUDING MUCH OF THE WILLAMETTE VALLEY WILL BE THE MAIN
FORECAST CHALLENGE FOR THE REMAINDER OF THE WEEK. HAVE ADJUSTED
TEMPS FOR A BIT WARMER ON THE HIGHER TERRAIN ABOVE THE LOWLAND
INVERSION...AND BIT COOLER THROUGH THE COLUMBIA GORGE AND INTERIOR
VALLEYS. PLENTY OF COOL AIR ON EAST SIDE...WHICH WILL SPILL
WESTWARD. WILL PUSH NIGHT TEMPS DOWN INTO THE 20S FOR MOST AREAS OF
LOWLANDS...BUT IN WIND SHELTERED AREAS MAY BE A BIT COLDER. ROCKEY
.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...AN UPPER LEVEL
RIDGE PERSISTS THROUGH THE FORECAST AREA THROUGH THE END OF THE WEEK.
MODELS VARY SIGNIFICANTLY WITH THE BREAKDOWN OF THE RIDGE NEXT
WEEKEND AND THE ARRIVAL OF ANY SUBSEQUENT SYSTEMS...AS SHOWN BY
INCREASING ENSEMBLE SPREADS. EXPECT A SLIGHT CHANCE OF PRECIP
SOMETIME LATE SAT/EARLY SUN THROUGH EARLY NEXT WEEK...WITH A STRONG
SYSTEM APPROACHING THE REGION BY MID NEXT WEEK. HAVE KEPT POPS
SLIGHTLY BELOW CLIMATOLOGY GIVEN THE CONTINUED INFLUENCE OF THE RIDGE
AND MODEL INCONSISTENCIES. RAMIREZ
&&
.AVIATION...WIDESPREAD LIFR THROUGHOUT THE INLAND VALLEYS AND MAINLY
VFR AT THE COAST. STILL HAVE WEAK ONSHORE LOW-LEVEL FLOW OVER THE
NORTH PART OF THE FORECAST AREA WHICH IS ALLOWING SOME STRATOCUMULUS
TO PERSIST ALONG THE S WA AND N OREGON COAST. SATELLITE FOG DEPTH
PRODUCT INDICATES TOPS RANGING FROM 200 TO 400 METERS OR ROUGHLY 600
TO 1200 FEET. EXPECT VALLEY IMPROVEMENT TO VFR AROUND 20Z IN THE
NORTH TO AS LATE AS 22Z AROUND KEUG. THERE IS A 50 PERCENT
PROBABILITY THAT KEUG MAY NOT SEE VFR TODAY. OFFSHORE GRADIENT PICKS
UP AFTER 00Z THU WHICH WILL ELIMINATE FOG THREAT FOR KPDX AND KTTD.
HOWEVER...EXPECT CENTRAL AND SOUTH VALLEY TO GO BACK DOWN TO LIFR IN
THE 00Z TO 06Z TIME PERIOD. INCREASING WIND NEAR KTTD AFTER 00Z THU
WITH GUSTS UP TO 30 KT BY 12Z.
KPDX AND APPROACHES...LIFR AS OF 16Z. THE FOG DEPTH PRODUCT FROM 12Z
SHOWED A DEPTH AROUND 200 TO 300 METERS OR 600 TO 900 FEET. USING
THIS AS INPUT INTO THE FOG BREAKOUT PROGRAM THE RESULT SHOWS
IMPROVEMENT TO VFR AROUND 20Z. OFFSHORE GRADIENT BEGINS TO DEVELOP
AROUND 00Z BUT DO NOT EXPECT IT TO REACH THE TERMINAL UNTIL 03Z OR
SO. THIS WILL KEEP FOG FROM RETURNING. WEISHAAR
&&
.MARINE...HIGH PRES OFFSHORE WILL SLOWLY SHIFT INLAND OVER PAC NW
OVER THE NEXT FEW DAYS. THIS WILL BRING LIGHT OFFSHORE WINDS INTO
THE WEEKEND. NO SIGNIFICANT MARINE CONCERNS THROUGH AT LEAST FRI.
WEISHAAR
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...DENSE FOG ADVISORY FOR WILLAMETTE VALLEY TIL 11 AM.
WA...DENSE FOG ADVISORY FOR CLARK COUNTY TIL 11 AM.
PZ...NONE.
&&
$$
MORE WEATHER INFORMATION ONLINE AT...
HTTP://WEATHER.GOV/PORTLAND
THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON FROM
THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS COMMONLY
REFERRED TO AS THE FORECAST AREA.
