Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 282242
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
240 PM PST FRI NOV 28 2014

.SYNOPSIS...A WELL-DEFINED COLD FRONT WILL MOVE SOUTHEAST ACROSS THE
FORECAST THIS AFTERNOON AND EVENING...FOLLOWED BY A SHARP DROP IN
TEMPERATURE OVERNIGHT. WELL BELOW NORMAL TEMPERATURES WILL PERSIST
THROUGH THE WEEKEND...WITH SNOW LEVELS HOVERING JUST ABOVE THE COAST
AND VALLEY FLOORS. MIXED RAIN AND SNOW SHOWERS WILL PERSIST INTO
SATURDAY AS AN UPPER LEVEL TROUGH PASSES THROUGH...WITH PERHAPS A
SLUSHY INCH OR TWO OF SNOW ACCUMULATION IN THE HIGHER HILLS. WET
SNOWFLAKES MAY MIX IN FROM TIME TO TIME DOWN TO THE VALLEY FLOORS.
HIGH PRESSURE WILL SETTLE IN EAST OF THE CASCADES SATURDAY NIGHT AND
SUNDAY...BRINGING STRONG AND CHILLY EAST WINDS THROUGH THE GORGE AND
ACROSS THE PORTLAND METRO AREA. A SYSTEM COMING UP FROM THE SOUTH IS
LIKELY TO SPREAD MOISTURE OVER THE COLD AIR MONDAY...POSSIBLY
RESULTING IN SOME FREEZING RAIN NORTH OF SALEM DURING THE MORNING...
ESPECIALLY IN AND NEAR THE GORGE.

&&

.SHORT TERM...TONIGHT THROUGH MONDAY...A POTENT FRONTAL SYSTEM
EXTENDS FROM ABOUT KELSO TO TILLAMOOK AT THE MOMENT...PRESSING
SOUTHEASTWARD AT ABOUT 20-25 MPH. THE FRONT SHOULD BE THROUGH
PORTLAND AROUND 4-5 PM AND EUGENE AROUND 10-11 PM. GUSTY SOUTH WINDS
CONTINUE AHEAD OF THE FRONT...WITH WINDS GENERALLY GUSTING 30-40 MPH
BOTH IN THE WILLAMETTE VALLEY AND ALONG THE COAST. BEHIND THE FRONT
AN ABRUPT SHIFT TO GUSTY NORTHWEST WINDS OCCURS...ALONG WITH A QUICK
5-10 DEGREE F TEMPERATURE DROP. BY WEST COAST STANDARDS...THIS IS A
FAIRLY WELL-DEFINED COLD FRONT.

DESPITE THE SHARP DROP IN TEMPERATURE ASSOCIATED WITH THE FRONT...A
LOOK AT WSDOT WEBCAMS SHOWS SNOW IS ONLY FALLING TO ABOUT 3000 FEET
AT STEVENS PASS ROUGHLY 3 HOURS AFTER THE COLD FRONT MOVED THROUGH.
WE INITIALLY HAD SOME CONCERN THAT SNOW LEVELS WOULD DROP QUICKLY
ENOUGH TO PROVIDE ADVISORY ACCUMULATIONS FOR OUR CASCADES AND
FOOTHILL ZONES...BUT BASED ON WHAT IS HAPPENING TO OUR NORTH IT
APPEARS POST-FRONTAL SNOW ACCUMULATIONS SHOULD BE LIMITED TO A COUPLE
INCHES OR SO. TEMPERATURES HAVE ONLY FALLEN INTO THE LOWER 40S BEHIND
THE FRONT IN THE LOWLANDS AROUND SEATTLE...SO IT APPEARS UNLIKELY
THAT OUR VALLEYS WILL SEE SNOW FROM THE INITIAL SHOT OF PRECIPITATION
ASSOCIATED WITH THE FRONT.

COLD ADVECTION WILL CONTINUE TONIGHT...BUT SHOWERS ARE EXPECTED TO
DECREASE IN THE SUBSIDENCE BEHIND THE FRONT. HOWEVER THE MAIN UPPER
TROUGH WILL SWING THROUGH THE PAC NW SATURDAY...CAUSING A RESURGENCE
IN SHOWER ACTIVITY. WITH TEMPS MAINLY IN THE 30S WET SNOWFLAKES WILL
BE POSSIBLE DOWN TO THE VALLEY FLOORS...HOWEVER STICKING SNOW SHOULD
BE RELEGATED TO THE HILLS. THE WEST HILLS OF PORTLAND AND THE
CASCADE/COAST RANGE FOOTHILLS SURROUNDING THE WILLAMETTE VALLEY COULD
SEE AN INCH OR TWO OF ACCUMULATION...BUT IT SHOULD MAINLY BE ON
GRASSY SURFACES DUE TO OUR RECENT WARM SPELL. ABOVE 1000-1500 FT IS
WHERE SNOW MAY START TO STICK ON THE ROADS AND PRESENT TRAVEL
ISSUES...THOUGH THERE MAY BE SOME SUN BREAKS BETWEEN THE SHOWERS TO
MITIGATE THIS SATURDAY AFTERNOON.

COLD HIGH PRESSURE WILL SETTLE IN SAT NIGHT/SUNDAY FOR DRIER WEATHER.
AS HIGH PRESSURE STRENGTHENS EAST OF THE CASCADES... EASTERLY
PRESSURE GRADIENTS WILL RAMP UP THROUGH THE COLUMBIA GORGE. STRONG
AND CHILLY EAST WINDS WILL RESULT...AND THE COLD POOL AGAIN APPEARS
DEEP ENOUGH FOR THE EAST WINDS TO AFFECT THE WHOLE PORTLAND/VANCOUVER
METRO AREA. WITH THE 12Z 4KM UW WRFGFS KTTD-KDLS PRESSURE GRADIENTS
APPROACHING -9 TO -10 MB AND KOTH-KGEG PRESSURE GRADIENTS APPROACHING
-17 TO -19 MB...THIS EAST WIND EVENT IS NOT EXPECTED TO BE QUITE AS
STRONG AS OUR BIG EAST WIND EVENT EARLIER THIS MONTH BUT IT WILL
STILL BE FORMIDABLE. EXPECT EAST WIND GUSTS 60-70 MPH IN THE WEST END
OF THE COLUMBIA GORGE AND GUSTS 40-50 MPH IN THE GREATER
PORTLAND/VANCOUVER METRO AREA. THIS WOULD WARRANT A WIND
ADVISORY...WHICH MAY BE ISSUED BY SUBSEQUENT SHIFTS IF MODELS
CONTINUE TO PROJECT OFFSHORE GRADIENTS OF THIS MAGNITUDE.

THE STRONG EAST WINDS WILL DRY OUT OUR AIR MASS SUNDAY...ALLOWING
TEMPS TO FALL BELOW FREEZING MOST AREAS SUNDAY NIGHT. MODELS ARE MORE
OR LESS IN CONSENSUS NOW THAT SOME PRECIPITATION WILL SPREAD
NORTHWARD ACROSS OUR FORECAST AREA MONDAY MORNING. WITH THE
COMBINATION OF COLD AIR IN PLACE AND OVERRUNNING PRECIPITATION...
THERE IS SOME CONCERN FOR FREEZING RAIN IN OUR NORTHERN VALLEYS. THE
GREATEST THREAT IS IN AND NEAR THE GORGE WHERE COLD AIR WILL BE MOST
STUBBORN. HOWEVER THERE IS STILL A LOT OF UNCERTAINTY AS TO HOW THIS
EVENT WILL PLAY OUT...BUT FOR NOW WE INCREASED POPS...FREEZING RAIN
CHANCES...AND POTENTIAL ICE ACCUMULATIONS IN THE GRIDS MONDAY. KEPT
ICE ACCUMULATIONS FAIRLY MINIMAL AT THIS POINT DUE TO THE
UNCERTAINTY...THOUGH IF CURRENT MODELS ARE TO BE BELIEVED THERE COULD
BE MORE SIGNIFICANT ICING THAN PRESENTLY FORECAST.  WEAGLE

.LONG TERM...MONDAY NIGHT THROUGH FRIDAY...EXTENDED MODELS ARE IN
DECENT AGREEMENT HAVING THE NEXT PACIFIC FRONTAL SYSTEM LIFT A WARM
FRONT INTO THE PACIFIC NORTHWEST LATE MONDAY INTO TUESDAY MORNING.
12Z MODELS SUGGEST THE FRONT WILL STALL OVER THE REGION THROUGH
MIDDAY TUESDAY...WITH A GOOD AMOUNT OF QPF DUMPED OVER THE CENTRAL
PART OF THE FORECAST AREA. PREVAILING EAST WINDS WILL CONTINUE
THROUGH THE COLUMBIA RIVER GORGE...AND AS THE PRECIP LIFTS NORTH-
NORTHEAST OVER THE AREA...COULD SEE SOME THREAT FOR FREEZING RAIN
OVER THE UPPER HOOD RIVER VALLEY AND THE GORGE MONDAY NIGHT. THIS
WILL BE SHORT-LIVED AS MODELS DRAG THE PARENT LOW FURTHER SOUTH
ALONG THE CALIFORNIA COAST LATE TUESDAY. MODEL SOLUTIONS DIVERGE
STARTING WEDNESDAY...AS UPPER LEVEL ONSHORE FLOW DEVELOPS. STILL LOW
CONFIDENCE CONCERNING THE OVERALL TRACK OF THIS PACIFIC SYSTEM. IT
COULD EITHER PUSH ONSHORE INTO NORTHERN CALIFORNIA AND MAINTAIN
SEASONABLY WET CONDITIONS AS THE 12Z ECMWF SUGGESTS...OR THE LOW
COULD PUSH INLAND OVER CENTRAL CALIFORNIA WITH MUCH OF THE PRECIP
STAYING SOUTH OF OUR AREA AS THE 12Z GFS SUGGESTS. WENT MORE TOWARDS
CLIMO FOR THE END OF THE WEEK. /27

&&

.AVIATION...WIDESPREAD MVFR CIGS WITH FEW POCKETS OF IFR THIS
AFTERNOON. AT 2 PM...COLD FRONT EXTENDED FROM JUST N OF KTMK TO
KKLS TO MT RAINIER. THIS FRONT WILL PUSH S ACROSS NW OREGON THIS
EVENING. ONCE FRONT PUSHES S...AREAS BEHIND THE FRONT WILL SLOWLY
IMPROVE TO MVFR AND LOW VFR THAT WILL PERSIST INTO SAT AM. EXPECT
HIGHER TERRAIN TO BE OBSCURED IN PRECIP AND CLOUD THROUGH SAT AM.
COLD AIR SPREADING INTO REGION LATER TONIGHT...WITH MIX OF SNOW
AND RAIN DOWN TO VALLEY FLOORS EARLY SAT. SKIES WILL GRADUALLY
CLEAR FROM N TO S SAT AFTERNOON AND DRIER AIR ARRIVES.

KPDX AND APPROACHES...BREEZY AND RAINY WITH MVFR INTO EARLY THIS
EVENING. FRONT WILL MOVE ACROSS OPS AREA BETWEEN 00Z AND 02Z.
WINDS WILL TURN W OR NW...WITH RAIN DECREASING AFTER 04Z. WILL
SEE LOW VFR WITH OCCASIONAL MVFR AND SHOWERS INTO SAT AM. WILL SEE
SNOW IN SHOWERS AFTER 12Z...BUT NO ACCUMULATIONS EXPECTED AS
GROUND REMAINS TOO WARM. DRYING AND VFR AFTER 20Z SAT. ROCKEY.

&&

.MARINE...BREEZY S WINDS ON THE COASTAL WATERS...WITH GUSTS 25 TO
30 KT. STRONGEST WINDS WILL BE CLOSE TO SHORE THROUGH EARLY THIS
AFTERNOON. AT 2 AM FRI...THE STRONG COLD FRONT WAS JUST N
TILLAMOOK...AND WILL CONTINUE PUSHING SOUTHWARD THROUGH THIS
EVENING. WINDS WILL TURN NW BEHIND THE FRONT...AND REMAIN GUSTY
THROUGH SAT AM.

SEAS RUNNING 11 TO 14 FT INTO EARLY THIS EVENING...BUT WILL SLOWLY
SUBSIDE TONIGHT AND SAT. HOWEVER...LIKELY TO HOLD CLOSE TO 10 FT
ON THE WATERS THROUGH SAT AFTERNOON.

WINDS EASE LATER SAT AND SAT NIGHT...WITH GRADIENTS BECOMING
OFFSHORE AND STRENGTHENING AS HIGH PRES BUILDS OVER PAC NW. LIKELY
SEE GUSTS 20 TO 30 KT IN THE COASTAL GAPS ON SUN AND SUN NIGHT.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS ON ALL WATERS THROUGH SAT AM.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS ON ALL WATERS THROUGH
      SAT AFTERNOON.
     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR TONIGHT
      THROUGH SAT AM.

&&

$$

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.


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