FXUS66 KPQR 112230
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
229 PM 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...NOT A LOT OF CHANGE FROM WHAT I SPOKE ABOUT THIS
MORNING SO WILL ELABORATE ON SOME EXTRA FUN DETAILS. THE UPPER HOOD
RIVER VALLEY IS IN A FAVORABLE POSITION FOR DECENT UPSLOPE COMBINED
WITH THE EASTERN EDGE OF DEFORMATION WHICH WILL ENHANCE SNOWFALL IN
THAT AREA. BECOMING CLEAR THAT DEFORMATION BAND WILL BE OVER CENTRAL
OR NORTHERN WILLAMETTE VALLEY THUS UPGRADED ADVISORIES TO WARNINGS
FOR CENTRAL AND NORTH WILLAMETTE VALLEY. ALSO GORGE WILL SEE SOME OF
THE DEFORMATION BANDS INFLUENCE. ALREADY SEEING SOME SNOWFLAKES FROM
OBSERVERS NEAR EUGENE. STILL BELIEVE 4 TO 8 INCHES AND POSSIBLY MORE
IS NOT OUT OF THE QUESTION FOR THE AREA UNDER THE DEFORMATION
BAND...STILL MOST LIKELY JUST SE OF THE PORTLAND METRO AREA THOUGH
STILL NOT EXTREMELY CLEAR. 2 TO 4 INCHES STILL SEEMS REASONABLE FOR
PORTLAND METRO AREA EVEN IF THE BAND DOES NOT PASS DIRECTLY OVER THE
AREA. SALEM WILL BE A MESS WITH WHEN TO TRANSITION OUT OF
FZRA...LIKELY AROUND 6 PM SATURDAY. NORTH COAST SHOULD NOT SEE MUCH
PRECIPITATION THOUGH IT IS COLD ENOUGH THAT ANY THAT DOES FALL WILL
BE FROZEN ESPECIALLY IF WE MAINTAIN OFFSHORE FLOW AS MODELS SUGGEST.
OTHER INTERESTING MODEL PARAMETERS...A LOT OF VERTICAL VELOCITY AT
700 MB SETS UP RIGHT OVER PORTLAND INDICATING LIFT FROM DEFORMATION
BAND. FURTHER DECENT LIFT IN THE DENDRITIC GROWTH ZONE WITH 6
MICROBAR PER SECOND LIFT IN SATURATED AIR BETWEEN -10 AND -15 C OVER
MUCH OF THE VALLEY TONIGHT. WRFGFS BRINGS LITTLE SNOW TO VALLEY FLOOR
BUT BELIEVE IT IS WAY TO FAST IN SCOURING COLD LAYER. AND IF COLD AIR
STAYS AND PRECIP IS CORRECT...WRFGFS WILL GIVE PORTLAND A GOOD DOSE
OF SNOW BRINGING DEFORMATION BAND RIGHT OVER THE METRO AREA. WOLFE
THATS ALL FOR THE UPDATE.
PREVIOUS DISCUSSION FOLLOWS...
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...EXTENDED MODELS REASONABLY CONSISTENT THIS TIME AROUND.
UPPER FLOW TURNS TO THE W OR SW FOR MUCH OF NEXT WEEK...WITH THE
INITIAL PACIFIC FRONT PUSHING IN BY MON NIGHT. CHANCES FOR RAIN RUN
HIGHER THAN CLIMATOLOGY...WITH A RETURN TO MORE SEASONAL TEMPS.
OFFSHORE FLOW THROUGH THE GORGE AHEAD OF THE FIRST COLD FRONT
SUGGESTS STILL SOME POTENTIAL FOR FREEZING RAIN MON NIGHT AND
POSSIBLY INTO EARLY TUE. OVERALL LITTLE CHANGE PLANNED TO PREVIOUS
FORECAST.
&&
.AVIATION...PRECIP BAND HAS BEGUN TO MOVE INTO THE FAR SOUTH
REACHES OF THE FORECAST AREA...WITH VFR CIGS SOON TO GIVE WAY TO
MVFR AT KEUG AND ALREADY AT KONP. AS THE BAND MOVES NORTH...A MIX
OF WINTRY PRECIP WILL SPREAD NORTH THROUGH THE EVENING AND
OVERNIGHT...REACHING KPDX BY MIDNIGHT AND KAST SHORTLY THEREAFTER.
DEGRADING CONDITIONS SHOULD FOLLOW ALONG AND BEHIND THE
FRONT...WITH IFR CONDITIONS POSSIBLE MOST AREAS SOUTH OF KPDX BY
SAT MORNING. WINTRY CONDITIONS WILL CONTINUE THROUGH THE DAY SAT.
KPDX AND APPROACHES...VFR CONDITIONS WILL CONTINUE THROUGH THIS
EVENING. LIGHT OFFSHORE FLOW WILL BEGIN TO TURN SLY LATER THIS
EVENING. PRECIP REACHING KPDX BY OR JUST BEFORE MIDNIGHT...WITH
SNOW EXPECTED TO BE THE PRIMARY PRECIPITATION TYPE THROUGH THE
NIGHT. ACCUMULATIONS SHOULD BE SOMEWHAT LIGHT OVERNIGHT. SNOW MAY
BE MIXED WITH LIGHT FREEZING RAIN AT TIMES...THOUGH MOST LIKELY
TOWARDS SAT MORNING. BROWN
&&
.MARINE...LOW PRESSURE SYSTEM NOW NEAR 41N 130W 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.
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER STORM WARNING FROM 8 PM THIS EVENING TO 6 AM PST SUNDAY
FOR GREATER PORTLAND METRO AREA-UPPER HOOD RIVER VALLEY-
WESTERN COLUMBIA RIVER GORGE.
WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 6 AM PST
SUNDAY FOR NORTHERN OREGON CASCADE FOOTHILLS.
WINTER WEATHER ADVISORY UNTIL 8 AM PST SATURDAY FOR CASCADE
FOOTHILLS IN LANE COUNTY-CENTRAL COAST RANGE OF WESTERN
OREGON-SOUTH WILLAMETTE VALLEY.
WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 6 AM PST
SUNDAY FOR COAST RANGE OF NORTHWEST OREGON-LOWER COLUMBIA.
WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 10 PM PST
SATURDAY FOR NORTH OREGON COAST.
WINTER WEATHER ADVISORY UNTIL MIDNIGHT PST TONIGHT FOR CENTRAL
OREGON COAST.
WINTER STORM WARNING FROM 5 PM THIS AFTERNOON TO 10 PM PST
SATURDAY FOR CENTRAL WILLAMETTE VALLEY.
WA...WINTER STORM WARNING FROM 8 PM THIS EVENING TO 6 AM PST SUNDAY
FOR GREATER VANCOUVER AREA-WESTERN COLUMBIA RIVER GORGE.
WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 6 AM PST
SUNDAY FOR I-5 CORRIDOR IN COWLITZ COUNTY-SOUTH WASHINGTON
CASCADE FOOTHILLS.
WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 10 PM PST
SATURDAY FOR SOUTH WASHINGTON COAST.
PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 1 AM TO 4 PM PST SATURDAY
FOR 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.
