FXUS66 KPQR 252302
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
300 PM PST WED NOV 25 2009
.SYNOPSIS...A MOIST FRONTAL SYSTEM WILL SLOWLY APPROACH THE COAST
THIS EVENING...GRADUALLY SPREADING RAIN ONSHORE THROUGH THANKSGIVING
DAY. LOW PRESSURE IS DEVELOPING ALONG THE FRONT WELL OFF THE NORTHERN
CALIFORNIA COAST...AND WILL RIDE NORTHEAST ALONG THE FRONT AS IT
MOVES ONSHORE THURSDAY. THIS WILL PROVIDE A FOCUS FOR RAINFALL DURING
THE DAY THURSDAY...ESPECIALLY ALONG THE NORTHERN OREGON AND SOUTH
WASHINGTON COAST RANGE WHERE RAIN COULD BE LOCALLY HEAVY FOR A FEW
HOURS. RAIN WILL TAPER TO SHOWERS THURSDAY NIGHT AND FRIDAY AS THE
LOW PRESSURE AND FRONT MOVE EAST OF THE CASCADES. SNOW LEVELS WILL
FALL BELOW THE CASCADE PASSES BY FRIDAY MORNING...WITH A FEW INCHES
OF ACCUMULATION POSSIBLE. A STALLED FRONT MAY BRING MORE
PRECIPITATION MAINLY TO NORTHERN AREAS FOR THE WEEKEND...THEN A
DRIER WEATHER IS LOOKING POSSIBLE FOR MUCH OF NEXT WEEK.
&&
.SHORT TERM...IT WAS A WARM LATE NOVEMBER DAY TODAY IN MANY AREAS
ACROSS THE DISTRICT...ESPECIALLY IN THE FOOTHILLS JUST ABOVE THE
VALLEY INVERSIONS AND ALONG THE CENTRAL COAST. MANY OF THESE
LOCATIONS ROSE INTO THE 60S TODAY...WHILE PORTIONS OF THE WILLAMETTE
VALLEY REMAINED TRAPPED UNDER THE INVERSION AND STUCK IN THE 40S OR
LOWER 50S MUCH OF THE DAY.
MID TO HIGH LEVEL CLOUD COVER IS BEGINNING TO INCREASE THIS AFTERNOON
IN ADVANCE OF A SLOW MOVING COLD FRONT WHICH EXTENDS FROM VANCOUVER
ISLAND SOUTHWEST INTO THE PACIFIC. SATELLITE IMAGERY INDICATES LOW
PRESSURE IS BEGINNING TO DEVELOP ALONG THE FRONT IN THE VICINITY OF
40N/135W THIS AFTERNOON. THIS LOW WILL TRAVEL NORTHEAST ALONG THE
FRONT...LIKELY REACHING THE COAST SOMEWHERE BETWEEN HOQUIAM AND NORTH
BEND THURSDAY AFTERNOON. MODELS HAVE HAD A HARD TIME PINPOINTING THE
STRENGTH AND LANDFALL LOCATION OF THIS LOW...AS BOTH WILL BE STRONGLY
CORRELATED WITH ONE ANOTHER. FOR NOW...THE LATEST GFS/NAM/ECMWF ALL
KEEP THE LOW FAIRLY WEAK AS IT MOVES ONSHORE...WHICH WOULD FAVOR A
MORE SOUTHERN LANDFALL. IF THE LOW STRENGTHENS A BIT FASTER THAN THE
MODELS CURRENTLY INDICATE... WHICH SEEMS QUITE POSSIBLE GIVEN THE JET
ENERGY INJECTING INTO THE UPPER TROUGH OFFSHORE...THE LOW WOULD
PROBABLY MOVE ONSHORE FURTHER NORTH...CLOSER TO ASTORIA OR HOQUIAM.
THIS WOULD ALSO FAVOR STRONGER WINDS ALONG THE COAST AS THE LOW MAKES
LANDFALL...BUT AT THIS POINT IT APPEARS WINDS WILL REMAIN WELL BELOW
HIGH WIND WARNING CRITERIA. PERHAPS SOME GUSTS 35-45 MPH ALONG THE
COASTAL HEADLANDS SHOULD DO IT AS THE LOW AND FRONT MOVE ONSHORE THU
AFTERNOON AND EVENING.
THE LOW WILL ALSO PROVIDE A FOCUSING MECHANISM FOR RAINFALL...AS A
DECENT MOISTURE PLUME IS EVIDENT ON AMSU PRECIPITABLE WATER IMAGERY
EXTENDING FROM THE FRONT SW INTO THE SUBTROPICS. GFS SUGGESTS PW
VALUES AROUND 1.25-1.50 INCHES AS THE FRONT MOVES ONSHORE THURSDAY.
THIS MOISTURE RICH ENVIRONMENT COULD LEAD TO SOME PRETTY GOOD RAIN
RATES AS THE FRONT MOVES ONSHORE...ESPECIALLY IN THE NORTH COAST AND
COAST RANGE. IT STILL APPEARS SOME AREAS IN THE COAST RANGE COULD
RECEIVE AS MUCH AS 2-4 INCHES OF RAIN LOCALLY...WITH INLAND
LOCATIONS RECEIVING A BIT LESS...CLOSER TO ONE HALF TO ONE INCH. FOR
NOW...IT APPEARS THIS WILL NOT BE ENOUGH TO CREATE ANY MAJOR
HYDROLOGIC PROBLEMS IN OUR AREA...BUT WILL CONTINUE TO MONITOR AS IT
APPEARS THIS FRONTAL SYSTEM DOES HAVE ACCESS TO SOME SUBTROPICAL
MOISTURE.
INCREASING OROGRAPHICS AND LOWERING SNOW LEVELS SHOULD CAUSE A FEW
INCHES OF SNOW ACCUMULATION IN THE CASCADES LATER THU NIGHT INTO
FRI...BUT LATEST GUIDANCE SUGGESTS THE QPF WILL PROBABLY NOT BE
ENOUGH TO AVERAGE THE 6 INCHES PER 12 HOURS REQUIRED FOR A WINTER
WEATHER ADVISORY. SNOW LEVELS IN THE HEART OF THE COLD AIR COULD GET
AS LOW AS 1500 TO 2000 FEET...WHICH WOULD DUST THE HIGHER ELEVATIONS
OF THE COAST RANGE AND THE HIGHER CASCADE FOOTHILLS WITH SOME SNOW.
WEAGLE
.LONG TERM...MODELS IN FAIRLY GOOD AGREEMENT THROUGH THE EXTENDED
PERIOD. A BRIEF POST FRONTAL RIDGE WILL BRING GENERALLY MOSTLY
CLOUDY WEATHER TO THE FORECAST AREA SUNDAY AND MOST OF MONDAY. A
SHORTWAVE WILL PASS BY TO THE NORTH LATE MONDAY AND TUESDAY BRINGING
RAIN TO THE AREA...MAINLY TO THE NORTH PART. THE RIDGE APPEARS TO
REBOUND AGAIN FOR THE MIDDLE OF NEXT WEEK...WITH ALL MODELS COMING
INTO AGREEMENT FOR THIS SOLUTION THROUGH THE END OF THE WEEK. BROWN
&&
.AVIATION...THE NEXT FRONT STALLS OFFSHORE THIS EVENING...SLOWLY
WEAKENING AS IT MOVES INLAND TONIGHT. WHILE PASSING...WINDS VEER SE
AS AN UPPER LOW APPROACHES THE COAST THURS. RAIN AND LOW MVFR
CONDITIONS ARE POSSIBLE ALONG THE NORTH COAST EARLY THURS. MAINLY
VFR OVERNIGHT AND EARLY TOMORROW INLAND...UNTIL LOWER CLOUDS IMPACT
THE AREA AROUND 00Z FRIDAY.
KPDX AND APPROACHES...EXPECT VFR CONDITIONS OVERNIGHT AND EARLY
TOMORROW. MID LEVEL CLOUDS WILL INCREASE IN THE AFTERNOON.
&&
.MARINE...CONTINUATION OF SMALL CRAFT FOR HAZARDOUS SEAS CONTINUES
THROUGH THURS EVENING. SMALL CRAFT FOR WINDS BEGIN 18Z THURS...WITH
THE SOUTHERN WATERS IMPACTED BY THE NEXT FRONTAL SYSTEM FIRST. SEAS
SHOULD RISE TO NEAR 14 FT OVERNIGHT AS THE NEXT FRONTAL SYSTEM
ARRIVES. SOUTHERLY GALES ARE POSSIBLE THURS AS LOW PRES MOVES
INLAND...WITH BEST CHANCE SOUTH OF CASCADE HEAD. SEAS NOT LIKELY TO
DROP BELOW 10 FT UNTIL LATE WEEKEND OR EARLY NEXT WEEK.
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
WA/OR...SMALL CRAFT ADVISORY FOR WIND CAPE SHOALWATER
TO CASCADE HEAD THROUGH THIS EVENING...THEN AGAIN
THU AND THU EVENING.
SMALL CRAFT ADVISORY FOR WIND CASCADE HEAD TO FLORENCE
EARLY THU MORNING THROUGH THU EVENING.
SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS CAPE
SHOALWATER TO FLORENCE LATE THROUGH THU NIGHT.
SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR
CONDITIONS THROUGH LATE THU NIGHT.
&&
$$
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.
