FXUS66 KPQR 110455
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
855 PM PST THU DEC 10 2009
.SYNOPSIS...AN ARCTIC AIR MASS WILL CONTINUE OVER THE PACIFIC
NORTHWEST TONIGHT AND FRIDAY...AND BEGIN TO ERODE A BIT THIS WEEKEND.
A PACIFIC SYSTEM MOVING INTO CALIFORNIA TONIGHT AND FRIDAY WILL SEND
SOME MOISTURE NORTH OVER NORTHWEST OREGON AND SOUTHWEST WASHINGTON
BEGINNING LATE FRIDAY BUT MAINLY ON FRIDAY NIGHT. THIS WILL RESULT IN
A WINTRY MIX OF PRECIPITATION ACROSS THE FORECAST AREA. THE
PRECIPITATION WILL LIKELY CHANGE TO RAIN FROM THE SOUTH POSSIBLY AS
EARLY AS LATE FRIDAY NIGHT IN THE SOUTH BUT MORE LIKELY SLOWLY
THROUGH THE DAY ON SATURDAY...EXCEPT PERHAPS IN THE GORGE AND AND
NEAR THE WEST NED OF THE GORGE. HOWEVER THE DETAILS ARE VERY COMPLEX
AND THERE STILL EXISTS A DEGREE OF UNCERTAINTY IN HOW THIS SCENARIO
WILL PLAY OUT. SHOWERS WILL CONTINUE SUNDAY AND SUNDAY NIGHT AS A
COOL SYSTEM SWINGS THROUGH FROM THE NORTHWEST. A WARMER AND MORE
ORGANIZED SYSTEM IS EXPECTED FOR EARLY NEXT WEEK MONDAY NIGHT AND
TUESDAY...WITH A WINTRY MIX AGAIN POSSIBLE MAINLY IN THE GORGE AND
POSSIBLY NEAR THE WEST END OF THE GORGE.
&&
.SHORT TERM...CLEAR SKIES WITH AN ARCTIC AIR MASS SPELLS ANOTHER VERY
COLD NIGHT TONIGHT. ONE SLIGHT SAVING GRACE IS THAT DEW POINTS ARE
RUNNING 3 TO 7 DEGREES HIGHER THAN THOSE 24 HOURS AGO...SO EXPECT MIN
TEMPS TONIGHT TO AVERAGE AROUND 5 DEGREES WARMER THAN LAST NIGHT.
THAT IS STILL VERY COLD.
THE MODELS CONTINUE TO SHOW THAT A DEFORMATION BAND FROM A SYSTEM
MOVING WELL SOUTH INTO CALIFORNIA WILL LIFT NORTH THROUGH OUR AREA
MAINLY FRIDAY NIGHT. THE LEADING EDGE COULD REACH THE COTTAGE GROVE
AND EUGENE AREA LATE FRIDAY...AND UP NEAR PORTLAND PROBABLY AFTER
MIDNIGHT. WITH THE LOW DEWPOINTS AND THE FACT WE WILL JUST CROSS THE
FREEZING MARK FRIDAY AFTERNOON...WE WILL SEE A WINTRY MIX OF
PRECIPITATION AS THIS LIFTS NORTH. IN THE CENTRAL AND SOUTH
VALLEY...FOOTHILLS AND COASTAL MOUNTAINS IT WILL PROBABLY BE MAINLY A
FREEZING RAIN EVENT...THOUGH SOME BRIEF SNOW OR SLEET IS POSSIBLE
EARLY IN THE EVENT. WE COULD ALSO SEE SOME SNOW UP AGAINST THE EAST
SLOPES OF THE COASTAL MOUNTAINS FROM ABOUT MCMINNVILLE NORTH. NAM12
MODEL SOUNDINGS SUGGEST THE SOUTH VALLEY MAY TURN TO RAIN EITHER LATE
FRIDAY NIGHT OR MORE LIKELY SATURDAY MORNING...WITH THE CENTRAL
VALLEY MORE LIKE MID DAY OR SO. UP NORTH NEAR PORTLAND IT WILL BE
MORE SNOW AND LESS FREEZING RAIN INITIALLY...THEN TRANSITION TO MORE
FREEZING RAIN ON SATURDAY. AREAS AWAY FROM THE GORGE MAY EVEN SEE
RAIN LATE SATURDAY OR SATURDAY EVENING. THE GORGE AND UPPER HOOD
RIVER VALLEY PROBABLY WILL NOT GET OUT OF THE MIX THROUGH THE EVENT.
WILL NEED TO WATCH IF THE BAND STALLS IN THE SOUTH WASHINGTON
CASCADES...AS IF IT DOES...MAY NEED TO ISSUE SOMETHING THERE
EVENTUALLY.
ON SUNDAY AND SUNDAY NIGHT MORE SHOWERS ARE EXPECTED AS A VERY COOL
SHORT WAVE FROM THE NORTHWEST SWINGS THROUGH. THE SNOW LEVEL WILL BE
QUITE LOW BUT PROBABLY RAIN AT THE LOWEST ELEVATIONS AS THE LOW LEVEL
FLOW IS ONSHORE. THE NEXT SYSTEM FOR MONDAY NIGHT AND TUESDAY LOOKS
LIKE A WINTRY MIX FOR THE GORGE AND POSSIBLY NEAR THE WEST END AT
THIS POINT. TOLLESON
.LONG TERM...EXTENDED MODELS SHOWING A LITTLE MORE CONSISTENCY TODAY
AS OPPOSED TO PREVIOUS DAYS. GFS AND ECMWF OPERATIONAL RUNS CONTINUE
TO SUGGEST THE E PAC RIDGE SHIFTING E ACROSS THE REGION MON...
FOLLOWED BY WESTERLY FLOW ALOFT BREAKING THROUGH MON NIGHT WHICH
PUSHES A PACIFIC FRONTAL SYSTEM INLAND BY TUE. WITH THE OFFSHORE
FLOW AHEAD OF THIS SYSTEM...IT IS POSSIBLE THAT PRECIPITATION IN THE
GORGE COULD BE A WINTERY MIX AT THE BEGINNING OF THE EVENT MON
NIGHT.
DETAILS ARE LESS CLEAR BEYOND TUE...BUT THE COMMON GROUND IN THE
MODELS IS A CONTINUATION OF WESTERLY FLOW ALOFT. WILL TREND LATTER
PERIODS TOWARDS CLIMATOLOGY POPS AND TEMPS.
&&
.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 LATE TONIGHT AND EARLY FRI MORNING. INCREASING
MID TO HIGH LEVEL CLOUDS FROM THE SOUTH LATER FRI...POSSIBLY
RESULTING IN MIXED PRECIPITATION KEUG SOUTHWARD BY 23Z.
KPDX AND APPROACHES...VFR WITH OCCASIONAL EAST WIND THROUGH FRI
AFTERNOON. SOME HAZE/MIST MAY CAUSE VSBYS TO APPROACH 5SM FOR A
BRIEF PERIOD AROUND DAYBREAK. WEAGLE
&&
.MARINE...LIGHT TO MODERATE OFFSHORE FLOW WILL CONTINUE THROUGH
FRIDAY. POORLY ORGANIZED LOW PRESSURE SYSTEM OFF CALIFORNIA COAST
WILL DRIFT NE TOWARD CAPE BLANCO FRI. MUCH OF THE WIND AND SWELL
ENERGY ASSOCIATED WITH THIS SYSTEM WILL STAY SOUTH...AND IMPACT
CALIFORNIA. STRONGER LOW PRESSURE WILL MOVE INTO NORTHERN
CALIFORNIA SAT/SAT NIGHT...AGAIN AFFECTING MAINLY CALIFORNIA WITH
WIND AND SWELL. STORM TRACK IS EXPECTED TO LIFT FURTHER NORTH
EARLY NEXT WEEK...WITH A PACIFIC FRONTAL SYSTEM LIKELY TO IMPACT
THE PACIFIC NORTHWEST COASTAL WATERS WITH STRONGER WINDS AND SEAS
MONDAY AND TUESDAY. WEAGLE
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER STORM WATCH FROM FRIDAY EVENING THROUGH SATURDAY
AFTERNOON FOR COAST RANGE OF NORTHWEST OREGON-GREATER
PORTLAND METRO AREA-LOWER COLUMBIA-UPPER HOOD RIVER VALLEY-
WESTERN COLUMBIA RIVER GORGE.
WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SATURDAY
AFTERNOON FOR CENTRAL WILLAMETTE VALLEY-NORTHERN OREGON
CASCADE FOOTHILLS.
WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH LATE FRIDAY
NIGHT FOR CASCADE FOOTHILLS IN LANE COUNTY-CENTRAL COAST
RANGE OF WESTERN OREGON-SOUTH WILLAMETTE VALLEY.
WA...WINTER STORM WATCH FROM FRIDAY EVENING THROUGH SATURDAY
AFTERNOON FOR GREATER VANCOUVER AREA-I-5 CORRIDOR IN
COWLITZ COUNTY-WESTERN COLUMBIA RIVER GORGE.
WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SATURDAY
AFTERNOON FOR SOUTH WASHINGTON CASCADE FOOTHILLS.
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.
