FXUS66 KPQR 111700
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
859 AM PST FRI DEC 11 2009
.SYNOPSIS...A COLD AIR MASS WILL BE RELUCTANT TO MOVE OUT OF THE AREA
OVER THE NEXT COUPLE OF DAYS. IN THE MEANTIME A SYSTEM MOVING INTO
CALIFORNIA WILL ROTATE PRECIPITATION NORTHWARD OVER THE COLD AIR MASS
THE PRECIP THAT DOES FALL WILL BE FROZEN. DIFFICULT TO SAY IF ALL OF
THE COLD AIR WILL SCOUR BY SUNDAY AS ANOTHER WEAK SYSTEM SWINGS DOWN
FROM THE NORTH...THOUGH WITH ONSHORE FLOW BELIEVE ANY FROZEN PRECIP
WITH THIS SYSTEM WILL BE SHORT LIVED BEFORE CHANGING OVER TO RAIN.
NEXT WEEK LOOKS VERY WET WITH A LARGE TROPICAL SYSTEM MOVING INTO THE
REGION WHICH WILL LIKELY BRING A LOT OF QPF.
&&
.SHORT TERM...ALL FOCUS TURNS TO THE NEXT 36 TO 48 HOURS. IT APPEARS
MODELS ARE BEGINNING TO COME INTO AGREEMENT WITH THE TIMING OF THE
ONSET OF HEAVIER PRECIP BEING SOMETIME SATURDAY...HOWEVER...THERE
WILL BE A WEAKER BAND THAT MOVES THROUGH TONIGHT THAT WILL LIKELY BE
IN THE FORM OF SNOW THOUGH ACCUMULATIONS ARE NOT EXPECTED TO BE MUCH
WITH THIS WEAKER BAND.THOUGH TOMORROW WILL BE A DIFFERENT STORY.
ON SATURDAY MODELS HAVE REALIZED...AT LEAST A LITTLE...THE RELUCTANCE
OF THE COLD AIR TO LEAVE...AND THEREFORE THE PRECIP WILL LIKELY FALL
AS SNOW FROM SALEM NORTH. THAT BEING SAID THERE WILL BE A LOT OF
ACCUMULATION SOMEWHERE THOUGH GIVEN THE DYNAMIC FORCING MECHANISM...A
DEFORMATION BAND...WHICH ACTS TO INCREASE INSTABILITY OVER A NARROW
BAND...IT IS DIFFICULT TO NAIL DOWN WHERE THE HEAVIEST SNOW WILL
FALL. THE ORIENTATION OF THIS BAND WILL BE FROM THE SOUTHWEST TO
NORTHEAST AND AS OF NOW LOOKS LIKE IT WILL BE SOMEWHERE TO THE
SOUTHEAST OF THE PORTLAND METRO AREA. AS DETAILS UNFOLD...WILL TRY TO
ASSESS A MORE ACCURATE PLACEMENT THOUGH. THIS IS NOT TO SAY THAT
PORTLAND WILL NOT GET ANY ACCUMULATION AND ON THE OTHER HAND THE BAND
MAY VERY WELL SET UP OVER PORTLAND. SO BELIEVE A WARNING IS NECESSARY
FOR A LOCATION IN THE NORTH VALLEY OR CENTRAL VALLEY...AND WILL
REANALYZE THIS THIS MORNING BEFORE ISSUING.
THIS IS FOR CERTAIN...ALL MODELS HAVE INCREASED THE LONGEVITY OF THE
COLD AIR. THEY ALL HAVE INCREASED QPF AMOUNTS TO NEAR 0.40 INCHES TO
0.8 INCHES BY SUN MORNING WHICH TRANSLATES TO 4 TO 8 INCHES OF SNOW
IF IT ALL FALLS AS SNOW...EVEN IF IT FALLS AS ICE THIS WILL BE A
MESS. THE GOOD NEWS IS THE HEAVIEST AMOUNTS WILL BE SOMEWHAT LOCAL IN
NATURE. BECOMING FAIRLY CONFIDENT IN PRECIP TYPE. TIMING APPEARS TO
BE LIGHT PRECIP MOST OF THE DAY SATURDAY WITH A HEAVIER BAND SAT
NIGHT. LOW TO MODERATE CONFIDENCE IN WHERE THE HEAVIEST PRECIPITATION
WILL BE. LOW TO MODERATE CONFIDENCE IN WHEN PRECIP WILL CHANGE TO
FZRA OR RAIN IN THE NORTH IF EVER. MODERATE CONFIDENCE IN THE SOUTH
VALLEY.
QUICK PARAGRAPH ABOUT THE COAST...IF FLOW REMAINS OFFSHORE THERE WILL
LIKELY BE SOME FREEZING PRECIP THERE AS WELL THOUGH ACCUMULATIONS
SHOULD NOT BE TO THE MAGNITUDE OF THE VALLEY...MORE LIKE AN EIGHTH OF
AN INCH OF ICE.
PLEASE STAY TUNED AS THIS COMPLEX SCENARIO UNFOLDS IT HAS A LOT OF
POTENTIAL TO CREATE HAVOC IN SOME AREAS AND WILL LIKELY AFFECT MOST
OF THE FORECAST AREA IN ONE WAY OR ANOTHER. WOLFE
.LONG TERM...NO CHANGES...PREVIOUS DISCUSSION FOLLOWS. 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 DURING THE DAY TODAY. INCREASING MID TO HIGH LEVEL CLOUDS
FROM THE SOUTH LATER TODAY...POSSIBLY RESULTING IN MIXED
PRECIPITATION KEUG SOUTHWARD BY 22Z-00Z. MIXED PRECIP SPREADING
NORTH DURING THE EVENING AND OVERNIGHT.
KPDX AND APPROACHES...VFR WITH OCCASIONAL EAST WIND THROUGH THIS
AFTERNOON. PRECIP REACHING KPDX AROUND MIDNIGHT. SNOW WILL BE THE
PRIMARY PRECIPITATION TYPE BUT MAY BE MIXED WITH LIGHT FREEZING RAIN
AT TIMES...ESPECIALLY TOWARDS SAT MORNING.
&&
.MARINE...LIGHT TO MODERATE OFFSHORE FLOW WILL CONTINUE THROUGH
TODAY. POORLY ORGANIZED LOW PRESSURE SYSTEM OFF CALIFORNIA COAST
WILL DRIFT NE TOWARD CAPE BLANCO TODAY. MUCH OF THE WIND AND SWELL
ENERGY ASSOCIATED WITH THIS SYSTEM WILL STAY SOUTH. STRONGER LOW
PRESSURE WILL MOVE INTO NORTHERN CALIFORNIA SAT/SAT NIGHT...AGAIN
AFFECTING MAINLY CALIFORNIA WITH WIND AND SWELL. SCA WINDS WILL
SPREAD TO SOUTHERN WATERS LATE TONIGHT THROUGH SAT AFTERNOON.
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/RUTHFORD
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 6 PM PST
SATURDAY FOR COAST RANGE OF NORTHWEST OREGON-GREATER
PORTLAND METRO AREA-LOWER COLUMBIA-UPPER HOOD RIVER VALLEY-
WESTERN COLUMBIA RIVER GORGE.
WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 6 PM PST
SATURDAY FOR CENTRAL WILLAMETTE VALLEY-NORTHERN OREGON
CASCADE FOOTHILLS.
WINTER WEATHER ADVISORY FROM 2 PM THIS AFTERNOON TO 4 AM PST
SATURDAY FOR CASCADE FOOTHILLS IN LANE COUNTY-CENTRAL COAST
RANGE OF WESTERN OREGON-SOUTH WILLAMETTE VALLEY.
WINTER WEATHER ADVISORY FROM 2 PM THIS AFTERNOON TO MIDNIGHT PST
TONIGHT FOR CENTRAL OREGON COAST.
WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 1 AM PST
SATURDAY FOR NORTH OREGON COAST.
WA...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 6 PM PST
SATURDAY FOR GREATER VANCOUVER AREA-I-5 CORRIDOR IN COWLITZ
COUNTY-WESTERN COLUMBIA RIVER GORGE.
WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 6 PM PST
SATURDAY FOR SOUTH WASHINGTON CASCADE FOOTHILLS.
PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 1 AM TO 4 PM PST SATURDAY
FOR COASTAL COASTAL WATERS FROM CASCADE HEAD OR TO FLORENCE OR.
&&
$$
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.
