584
FXUS66 KPQR 271633
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
833 AM PST FRI NOV 27 2009
SYNOPSIS
SLOW MOVING FRONTAL SYSTEM HAS FINALLY MOVED SOUTH AND
EAST OF THE FORECAST AREA. SOME LINGERING WRAPAROUND MOISTURE FROM
THE ASSOCIATED LOW PRESSURE SYSTEM IS STILL KEEPING SOME AREAS OF
RAIN AND MOUNTAIN SNOW AROUND THE AREA THIS MORNING...BUT THESE
SHOWERS WILL GRADUALLY TAPER OFF AS THE DAY PROGRESSES. HIGH PRESSURE
WILL BUILD ACROSS OREGON THIS WEEKEND LEADING TO GENERALLY DRIER
WEATHER...BUT THE TAIL END OF A WARM FRONT MAY CLIP OUR NORTHERN
ZONES WITH CLOUDS AND POSSIBLE RAIN FOR THE NORTH COAST. LONG RANGE
MODELS SUGGEST A RELATIVELY DRIER WEATHER REGIME SHOULD LAST THROUGH
MUCH OF NEXT WEEK.
SHORT TERM
RAIN IS GRADUALLY TAPERING OFF FROM WEST TO EAST ACROSS
THE FORECAST AREA THIS MORNING...AS OUR SLOW MOVING FRONTAL SYSTEM
HAS FINALLY PUSHED EAST OF THE CASCADES. SATELLITE AND DOPPLER RADAR
STILL INDICATE A BAND OF WRAPAROUND/DEFORMATION RAINFALL...WHICH
MOVED THROUGH THE PDX-SLE-EUG AREA EARLIER THIS MORNING AND IS NOW
SLOWLY PROGRESSING INTO THE CASCADE FOOTHILLS. PRECIPITATION RATES
ARE RESPECTABLE WITHIN THIS DEFORMATION BAND... LOCALLY 0.10-0.20
INCH PER HOUR. AS THIS BAND MOVES INTO THE CASCADES...A QUICK BURST
OF A COUPLE INCHES OF SNOW IS POSSIBLE OVER THE NEXT FEW HOURS BEFORE
PRECIPITATION TAPERS OFF THIS AFTERNOON.
AS THE UPPER LEVEL TROUGH MOVES EAST OF THE DISTRICT THIS AFTERNOON
AND EVENING...HIGH PRESSURE WILL BUILD ACROSS OREGON AND BEGIN TO DRY
THINGS OUT FOR THE AREA. 12Z GFS ALREADY SHOWS SOME MODEST UPPER
LEVEL RIDGING BEGINNING TO DEVELOP INTO THE PACIFIC NORTHWEST
TONIGHT. AS UPPER RIDGING DEVELOPS...VALLEY INVERSIONS WILL
STRENGTHEN AND SO WILL THE LIKELIHOOD OF FOG IN THE VALLEYS. WITH THE
GROUND SO WET FROM RECENT RAINS...LONG NIGHTS...AND LOW DAYTIME SUN
ANGLES...THE CONDITIONS WILL BE NEAR IDEAL FOR PERSISTENT INVERSION
CONDITIONS TO DEVELOP IN THE INLAND VALLEYS. THIS WILL MAKE MAX
TEMPERATURE FORECASTING TRICKY FOR THE WEEKEND...BUT FOR NOW HIGHS IN
THE 40S AND LOWER 50S LOOK GOOD. THE INVERSION WILL PROBABLY ALSO
CAUSE AIR QUALITY TO DETERIORATE OVER THE NEXT FEW DAYS...ESPECIALLY
IN THE CENTRAL AND SOUTHERN WILLAMETTE VALLEY.
FURTHER NORTH IN OUR DISTRICT...SOME CLOUDS MAY MOVE IN FROM TIME TO
TIME THIS WEEKEND IN ASSOCIATION WITH THE TAIL END OF A WARM FRONT
AFFECTING MAINLY BRITISH COLUMBIA AND WASHINGTON. MODELS HAVE SHOWN
SOME DISAGREEMENT ON THE POSSIBILITY OF RAIN FOR OUR DISTRICT DUE TO
THE WARM FRONT...BUT THEY ALL AGREE THE BEST CHANCES WILL BE ALONG
OUR FAR NORTHERN COAST...FROM ASTORIA NORTHWARD. CURRENT FCST OF
CHANCE POPS NORTH COAST AND SLIGHT CHANCE OR NO MENTION OF RAIN
ELSEWHERE THIS WEEKEND LOOKS GOOD. AGAIN...PERSISTENT FOG AND
DETERIORATING AIR QUALITY WILL PROBABLY BE THE MAIN ISSUES FOR OUR
SOUTHERN VALLEY ZONES AS WE PROGRESS LATER INTO THE WEEKEND AND EARLY
NEXT WEEK. WEAGLE
LONG TERM
MODELS AGREE THAT AN UPPER LEVEL RIDGE WILL AMPLIFY
BEGINNING OF THE EXTENDED PERIOD. THIS BRIEF POST FRONTAL RIDGE WILL
BRING PARTLY CLOUDY WEATHER TO THE REGION BY SUN AFTERNOON. A BRIEF
SHORTWAVE PASSES TO THE NORTH OF THE PAC NW MON AFTERNOON. THIS
DISTURBANCE LEVELS THE UPPER RIDGE AT THIS TIME...AND CAUSES
DISAGREEMENT AMONG THE MODELS. GFS AMPLIFIED THE RIDGE SO MUCH...THE
SHORTWAVE IMPACTS ONLY THE FAR NORTH BORDER OF WASHINGTON. AGREED
MORE WITH THE ECMWF...WHERE THE SHORTWAVE FLATTENS THE RIDGE ENOUGH
TO BRING RAIN TO NW OREGON TUE. MODELS BECOME INCONSISTENT WITH A
SYSTEM EXPECTED TO APPROACH THE COAST FRI. GFS PUSHES THIS SYSTEM
THROUGH THE FORECAST AREA QUICKLY...HAVING THIS STRONG SYSTEM HOVER
OVER THE AREA FOR THE WEEKEND. ECMWF IS MORE CONSERVATIVE...KEEPING
THE SYSTEM STALL OFFSHORE THROUGH SAT. NEVERTHELESS...BOTH MODELS
SUGGEST A STRONG RIDGE RETURN ONCE AGAIN. LRAMIREZ
AVIATION
RATHER DISTINCT LINE EXISTS ALONG THE PRECIPITATION BAND
NOW OVER CASCADES FOOTHILLS. LOW MVFR AND RAIN TO THE EAST OF LINE
THAT TRANSITIONS QUICKLY TO SCATTERED TO BROKEN VFR TO THE WEST.
WILL SEE SCATTERED TO BROKEN VFR OVER ENTIRE AREA BY 19Z...AS LAST
TO IMPROVE WILL BE CASCADES EXTENDING SSW TOWARDS KEUG. SKIES
CLEARING AFTER 23Z AS AIR MASS STABILIZES. THIS CLEARING...COMBINED
WITH LIGHT WIND AND MOIST GROUND...WILL SET UP IDEAL CONDITIONS FOR
EXTENSIVE FOG LATER TONIGHT.
KPDX AND APPROACHES...VFR CONDITIONS TODAY INTO THIS EVENING WITH
LIGHT NWLY ONSHORE FLOW. EXPECT FOG AND IFR CONDITIONS TO DEVELOP
AFTER 09Z TONIGHT UNDER STABLE CONDITIONS.
MARINE...GRADIENTS TIGHT THIS AM
WITH GALE FORCE WIND GUSTS OVER
THE CENTRAL OREGON COASTAL WATERS. GRADIENT WILL GRADUALLY RELAX
TODAY...WITH GALE FORCE GUSTS ENDING MID MORNING. AFTERWARDS...WILL
MAINTAIN SMALL CRAFT ADVISORIES FOR WINDS AND SEAS THROUGH REST OF
THE DAY. WINDS DROP OFF THIS EVENING...BUT SEAS BIT SLOWER TO EASE.
SEAS BRIEFLY DROP BELOW 10 FT FOR APPROX 24 HOURS BEGINNING LATE
THIS EVENING...BUT RISE ABOVE 10 FT AGAIN BY LATE SAT.
PQR WATCHES/WARNINGS/ADVISORIES
WA/OR...GALE WARNING FOR COASTAL WATERS FROM CASCADE HEAD TO
FLORENCE UNTIL 10 AM THIS MORNING.
SMALL CRAFT ADVISORY FOR WIND CAPE SHOALWATER TO CASCADE
HEAD TODAY.
SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS CAPE SHOALWATER TO
FLORENCE THROUGH THIS EVENING.
SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA BAR CONDITIONS THRU
THIS EVENING.
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.
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