FXUS66 KPQR 101108
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
307 AM PST THU DEC 10 2009

.SYNOPSIS...AN ARCTIC AIR MASS WILL CONTINUE THROUGH THE END OF THE
WEEK. THE BRUNT OF A PACIFIC SYSTEM IS EXPECTED TO MOVE INTO
CALIFORNIA LATE FRIDAY...WITH SOME PRECIPITATION LIKELY MOVING UP
INTO THE REGION FRIDAY NIGHT AND SATURDAY. THIS PRECIPITATION MAY
START OUT AS A LIGHT WINTRY MIX SNOW OR FREEZING RAIN OVER
INLAND VALLEYS...WITH A WINTRY MIX POSSIBLY LINGERING INTO SATURDAY
NIGHT NEAR THE COLUMBIA GORGE. A LARGER WARMER SYSTEM IS EXPECTED FOR
EARLY NEXT WEEK.

&&

.SHORT TERM...ANOTHER COLD NIGHT LAST NIGHT...WITH MULTIPLE 
LOCATIONS RUNNING UP TO 4 DEGREES COOLER THAN THIS TIME YESTERDAY 
MORNING. LOWERED THIS MORNING/S MIN TEMPS A BIT TO ACCOUNT FOR THIS. 
SUBSEQUENTLY...THINK THE AFTERNOON HIGHS TODAY MAY ALSO BE 1-2 
DEGREES LOWER SO I ADJUSTED THOSE AS WELL. THOUGH IT SHOULD BE A FEW 
DEGREES WARMER TONIGHT...NO AIR MASS CHANGE TAKES PLACE SO EXPECT WE 
WILL ONCE AGAIN DROP INTO THE TEENS TONIGHT AND FRI MORNING.

BIGGEST SHORT-TERM FORECAST CONCERN REMAINS THE POSSIBILITY OF FROZEN
PRECIP DURING THE FRI/SAT TIME FRAME. AS NEXT SYSTEM PUSHES INTO
CALIFORNIA ON FRI...MODELS AGREE IN WANTING TO BRING ENERGY WITH THAT
SYSTEM NORTHWARD ACROSS THE FORECAST AREA. TIMING REMAINS AN ISSUE
WITH THIS FEATURE...WITH THE ECMWF...NAM AND CANADIAN FAVORING A
SLOWER AND MORE SOUTHERN SOLUTION WITH SYSTEM AND THUS A SLOWER
NORTHWARD PROGRESSION OF THE PRECIP INTO OUR AREA. ONCE AGAIN THE GFS
IS THE OUTLIER WITH REGARD TO TIMING AND HAVE STEERED AWAY FROM THIS.
AS SUCH...SHOULD SEE PRECIP BEGIN TO MOVE INTO THE SOUTHERN CWA BY
AROUND 06Z FRI EVENING. SWLY MID LEVEL FLOW WILL LIKELY WARM THE
COAST...COAST RANGE AND CASCADE FOOTHILLS UP ENOUGH FOR RAIN.
HOWEVER...OVERALL SURFACE FLOW WILL BE WEAK AND WILL LIKELY NOT SCOUR
OUT THE COLD AIR IN THE VALLEY...MAKING PRECIP TYPE A CONCERN THERE.
PRECIP WILL LIKELY START OFF AS SNOW DUE TO LOW WET BULB ZERO
HEIGHTS...THEN TRANSITION TO FREEZING RAIN AS H85 TEMPS WARM UP TO
SLIGHTLY ABOVE FREEZING. SINCE PRECIP WILL BE ARRIVING AT
NIGHT...HAVE GONE WITH A CHANCE OF RAIN/FREEZING RAIN OVERNIGHT
FRIDAY NIGHT IN THE SOUTH VALLEY. CURRENT MODEL RUNS SHOW PRECIP
MOVING NORTH DURING THE PRE-DAWN HOURS OF SATURDAY MORNING FOR A
SIMILAR PRECIP TRANSITION...SNOW/FREEZING RAIN CHANGING TO
RAIN/FREEZING RAIN. THE LAST PLACE TO TURN WOULD BE AREAS NEAR THE
WEST END OF THE GORGE. DEPENDING ON THE DEGREE OF MID LEVEL WARMING
AND PRECIP RATES...WHICH WILL BE LIGHT REGARDLESS...AREAS IN THE
PORTLAND METRO AND NEAR THE GORGE MAY NOT CHANGE FROM SNOW AT ALL.

AS ALWAYS...THE DEVIL IS IN THE DETAILS. UNFORTUNATELY THE DETAILS
REGARDING HOW THIS EVENT IS GOING TO UNFOLD ARE STILL NOT CLEAR.

NO CHANGES MADE TO SAT AND SUN. WILL LEAVE IN SOLID CHANCE POPS FOR
THE FORECAST AREA DUE TO MODEL DISCREPANCIES AND LEAVE IT AT THAT.
DALTON

.LONG TERM...TIMING OF FEATURES ARE DIFFERENT AMONGST VARIOUS MODELS
IN THE EXTENDED...AS IS USUAL...HOWEVER THE OVERALL TREND IS A MORE
PROGRESSIVE AND WET PATTERN BEGINNING EARLY NEXT WEEK. SHOULD SEE
TEMPS RETURN TO MORE NORMAL VALUES AND WILL LIKELY SEE A 2-3 FRONTS
MAKE THEIR WAY THROUGH THE AREA THROUGHOUT NEXT WEEK...WITH POSSIBLY
A BREAK IN THE RAIN CLOSER TO NEXT WEEKEND.  DALTON

&&

.AVIATION...OFFSHORE FLOW AND DRY AIR MASS WILL CONTINUE VFR 
CONDITIONS. VERY SHALLOW FREEZING GROUND FOG POSSIBLE IN WIND 
SHELTERED VALLEYS OF THE CENTRAL OREGON COAST RANGE AND THE SOUTH 
WILLAMETTE VALLEY. 

KPDX AND APPROACHES...VFR CONDITIONS FOR NEXT 24 HRS. LIGHT WINDS 
THROUGH MID MORNING THEN MODERATED EAST WINDS FROM THE GORGE WILL 
REACH KPDX. RUTHFORD

&&

.MARINE...OFFSHORE FLOW IS KEEPING THINGS QUIET OVER THE WATERS WITH 
EAST WINDS AROUND 15 KT AND WEST SWELL 5 TO 6 FEET. SEAS WILL DROP 
TO 3 TO 4 FT AND REMAIN IN THAT RANGE THROUGH SAT. WITH THE NEXT LOW 
TRACKING SOUTH OF THE AREA AND INTO NORTHERN CALIFORNIA...LIGHT TO 
MODERATE E TO NE WINDS WILL PREVAIL THROUGH SAT THEN BACK MORE N TO 
NW AS THE LOW MOVES INLAND SUN. MUCH OF THE SWELL ENERGY FROM THIS 
SYSTEM WILL STAY SOUTH OF OREGON. SOUTHERLY WINDS OF 25 TO 30 KT 
WILL RETURN TO THE AREA MON OR TUE AS THE JET STREAM LIFTS NORTH. 
RUTHFORD

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR/WA...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.