Strong Wind in Oregon, December 2, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
855 AM PST TUE DEC  2 2014

.SYNOPSIS...OFFSHORE LOW-LEVEL FLOW WILL STRENGTHEN TODAY...THEN
SLOWLY WEAKEN TONIGHT AND WEDNESDAY. AN OCCLUDED FRONT WILL APPROACH
FROM THE SOUTH LATE THIS EVENING AND SPREAD LIGHT ACCUMULATING RAIN
FROM SOUTH TO NORTH LATE TONIGHT THROUGH WEDNESDAY MORNING. SURFACE
TEMPERATURES MAY REMAIN NEAR FREEZING AS THE PRECIPITATION ARRIVES
NEAR SALEM AND OVER IN THE CASCADE FOOTHILLS WITH THE POSSIBILITY OF
PATCHY FREEZING RAIN EARLY WEDNESDAY MORNING. RAIN CHANCES WILL
INCREASE WEDNESDAY NIGHT AND THURSDAY AS A LOW OFF THE CENTRAL OREGON
COAST WEDNESDAY DRIFTS NORTH TO NORTHEAST. FRIDAY WILL BE MOSTLY DRY
BEFORE A STRONGER FRONT ARRIVES FRIDAY EVENING. UNSETTLED WEATHER
CONTINUES THROUGH THE WEEKEND.

&&

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT...MINIMAL CHANGES TO THE
ONGOING SHORT TERM FORECAST. THE BIG PICTURE CONSISTS OF A CLOSED LOW
CENTERED NEAR 35N 131W WITH CONSIDERABLE MOISTURE STREAMING INTO
CALIFORNIA AND EXTREME SW OREGON. MUCH DRIER AIR ALOFT...AS SEEN IN
THE LATEST WATER VAPOR IMAGERY...IS OVER SRN WA AND NRN OREGON THIS
MORNING. KRTX DOPPLER RADAR NOT SHOWING ANY PRECIPITATION ECHOES AS
OF 1630Z BUT INFRA-RED SATELLITE IMAGERY INDICATES PLENTY OF MID AND
HIGH CLOUDS OVER THE SRN HALF OF THE FORECAST AREA. FOG PRODUCT
SHOWED AREAS OF LOW CLOUDS OVER THE S WILLAMETTE VALLEY AND INTO THE
CENTRAL OREGON CASCADE FOOTHILLS.

MAIN WEATHER FEATURE TODAY WILL BE THE INCREASING OFFSHORE LOW-LEVEL
FLOW. THE 16Z KTTD-KDLS GRADIENT WAS AT -7.4 MB...PRETTY CLOSE TO THE
12Z NAM INITIALIZATION. NAM SHOWS THIS GRADIENT STRENGTHENING
TODAY...PEAKING AT CLOSE TO -10 MB LATE THIS AFTERNOON AND EVENING.
NWS PORTLAND RULES OF THUMB SUGGEST A -10 MB GRADIENT WILL PRODUCE
PEAK GUSTS 70-80 MPH IN THE WINDIEST PART OF THE COLUMBIA GORGE...
AND AREAS LIKE CROWN POINT. ALSO...A GRADIENT OF THIS MAGNITUDE TENDS
TO PRODUCE GUSTS 40-45 MPH AT KTTD. WRF TIME-HEIGHT SECTION FOR KTTD
SHOWS A CORE OF 40-45 KT WIND SPEEDS 00Z-09Z WED FROM ABOUT 975 MB TO
935 MB. THIS APPEARS TO BE A GAP WIND EPISODE AND NOT A MORE
WIDESPREAD MOUNTAIN WAVE EVENT. CONTEMPLATED THE NEED FOR A WIND
ADVISORY FOR THE USUAL SUSPECT PORTIONS OF THE N WILLAMETTE VALLEY
NEAR THE GORGE AND IN CLARK COUNTY BUT WILL HOLD OFF. A COUPLE THINGS
GOING AGAINST MAJOR IMPACTS DESPITE THE FACT THIS LOOKS TO BE SIMILAR
IN MAGNITUDE TO THE EVENT THIS PAST WEEKEND. MOST OF THE LEAVES ARE
OFF THE TREES...IT HAS BEEN RELATIVELY DRY FOR THE PAST WEEK THUS
SOILS ARE OVERLY SATURATED AND PEAK GUSTS EXPECTED TO BE GENERALLY IN
THE 35-45 MPH. IT IS LIKELY THERE WILL BE LOCAL AREAS IN THE EAST
PORTLAND METRO AND VANCOUVER AREAS THAT GET GUSTS OVER 45 MPH...BUT
DO NOT THINK COVERAGE WILL BE SUCH TO WARRANT AN ADVISORY.

THE OTHER SHORT-TERM ISSUE IS THE THREAT OF FREEZING PRECIPITATION
LATE TONIGHT AND WED MORNING. LATEST MODEL RUNS SHOW THE LOW OFF THE
N CALIFORNIA COAST SLOWLY DRIFTING N TO NE TONIGHT. DIFFLUENT FLOW
ALOFT ON THE N PERIPHERY OF THE LOW...OVER SRN OREGON THIS
EVENING...GRADUALLY SHIFTS N TONIGHT. MID AND HIGH CLOUDS EXPECTED TO
INCREASE FROM THE S TONIGHT...BUT LIMITED OVER FAR NWRN OREGON AND
INTO SW WA DUE TO THE STRONG LOW-LEVEL OFFSHORE FLOW. TRICKY PART IS
DETERMINING THE EXACT EXTENT OF PRECIP. AREAS IN THE CENTRAL
WILLAMETTE VALLEY AND ADJACENT CASCADE FOOTHILLS SHOULD DIP AT OR
JUST BELOW FREEZING BEFORE THE CLOUD SHIELD ARRIVES. THE 00Z NAMM
SOUNDING FOR KSLE BRINGS PRECIP TO KSLE AROUND 17Z...LATE ENOUGH TO
FALL AS RAIN. HOWEVER...SHOULD PRECIP OCCUR AN HOUR OR TWO
EARLIER...THE SOUNDING WOULD SUGGEST A THREAT OF LIGHT -FZRA. ANY
ACCUMULATIONS LOOK TO BE VERY LIGHT...SIMILAR TO MONDAY MORNING...
BUT MAY STILL RESULT IN VERY SLICK ROADS.

THE RAIN CHANCES WILL INCREASE WEDNESDAY NIGHT THROUGH THURSDAY
MORNING AS THE LOW MOVES NORTHWARD OFFSHORE THE OREGON COAST. SNOW
LEVELS SHOULD WARM ABOVE THE CASCADE PASSES BY THIS TIME WITH RAIN
MELTING ANY LOWER ELEVATION SNOW. SHOWERS WILL DECREASE FROM THE
SOUTH TO THE NORTH THURSDAY NIGHT. WEISHAAR

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...MODELS
CONTINUE TO SHOW AN ACTIVE WEATHER PATTERN THROUGHOUT THE EXTENDED
FORECAST. EXPECT TEMPERATURES TO WARM TOWARDS SEASONAL NORMALS BY THE
END OF THE WEEK. TEMPERATURES OVER THE WEEKEND MAY DROP
SLIGHTLY...BUT NOT BY MUCH. NUMEROUS FRONTAL SYSTEMS WILL KEEP AT
LEAST A CHANCE OF RAIN OVER THE REGION INTO THE BEGINNING OF NEXT
WEEK. /64

&&

.AVIATION...SOME SCATTERED FOG AROUND THE AREA...BUT NORTHERN
SITES MAINLY VFR. WINDS AT KTTD CURRENTLY GUSTING TO 30 KTS...AND
AS THE EAST-WEST PRESSURE GRADIENT INCREASES TODAY THESE WINDS
SHOULD MAKE IT IN TO KPDX. EXPECT WINDS GUSTING TO 35 TO 40 KT THIS
AFTERNOON AT THESE TWO SITES. SOUTHERN WILLAMETTE VALLEY CURRENTLY
HAS MVFR CIGS...AND SHOULD REMAIN MVFR/IFR FOR MOST OF THE DAY
TODAY AS LOW STRATUS DOES NOT SEEM LIKELY TO CLEAR OUT. COASTAL
SITES TO STAY VFR TODAY AS DRY EASTERLY WINDS ARE KEEPING ANY LOW
CLOUDS FROM FORMING.

KPDX AND APPROACHES...SKY IS MOSTLY CLEAR ALOFT BUT KPDX AND
CAMERAS SHOW SCATTERED FOG IN THE AREA. THIS SHOULD BE MOSTLY CLEARED
OUT BY 18Z. WINDS LOOK TO PICK UP AROUND 21Z OUT OF THE EAST THIS
AFTERNOON...GUSTING TO 35 KT THIS EVENING.

-MCCOY

&&

.MARINE...WINDS OVER THE OUTER WATERS GUSTING TO 25 KT. THIS
SHOULD REMAIN CONFINED TO THE OUTER WATERS...THOUGH A FEW GUSTS TO
25 KT WILL LIKELY BE OBSERVED NEAR COASTAL TERRAIN GAPS. CLOSED
LOW PRESSURE SYSTEM WEAKENS AS IT SLOWLY DRIFTS OFF TO THE
NORTHEAST OVER THE NEXT TWO DAYS. BEHIND THIS SYSTEM THE WEATHER
PATTERN BECOMES MORE ACTIVE AS A STRONGER SYSTEM APPROACHES LATE
THIS WEEK. THIS SYSTEM WILL LIKELY BRING SMALL CRAFT ADVISORY WINDS
AND SEAS...THOUGH THE NEXT SYSTEM LATE THIS WEEKEND COULD
POTENTIALLY BRING SOME GALES. LOTS OF UNCERTAINTY IN THE FORECAST
EXISTS IN TIMING AND STRENGTH OF THESE SYSTEMS AS THEY ARE FAR OUT
IN THE FORECAST PERIOD.

SEAS LOOK TO REMAIN BELOW 10 FT THROUGH FRIDAY...APPROACHING 10
FT AHEAD OF THE AFOREMENTIONED FRONTAL SYSTEM LATE THIS WEEK. SEAS
COULD REMAIN AROUND 10 FT THROUGH THE WEEKEND.

-MCCOY

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 10 PM PST THIS EVENING FOR
     WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR FROM 10
     TO 60 NM-WATERS FROM CASCADE HEAD TO FLORENCE OR FROM 10 TO
     60 NM.

&&

INTERACT WITH US VIA SOCIAL MEDIA
WWW.FACEBOOK.COM/NWSPORTLAND
WWW.TWITTER.COM/NWSPORTLAND

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.