Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 272252
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
251 PM PST SAT DEC 27 2014

.SYNOPSIS...A COLD FRONT IS PUSHING DOWN THE BRITISH COLUMBIA COAST
THIS MORNING...AND WILL SPREAD RAIN AND MOUNTAIN SNOW SOUTHWARD
ACROSS THE FORECAST AREA TODAY AND TONIGHT. A TRAILING SECONDARY WAVE
WILL MAINTAIN SHOWERS SUNDAY INTO MONDAY. SNOW LEVELS WILL BE LOW
ENOUGH TO AFFECT THE CASCADE PASSES AND POSSIBLY SOME OF
THE HIGHER FOOTHILLS THIS WEEKEND. COLD AIR BEHIND THE FRONT WILL
DROP SNOW LEVELS FURTHER MONDAY MORNING...POSSIBLY MIXING SOME WET
SNOW DOWN TO THE VALLEY FLOOR AS SHOWERS TAPER OFF MONDAY. AT THIS
POINT VALLEY ACCUMULATIONS ARE NOT EXPECTED...BUT THE HILLS COULD GET
A DUSTING MONDAY MORNING. COLD AND DRY AIR WILL THEN DOMINATE MUCH OF
THE UPCOMING WEEK...WITH GUSTY NORTHEAST WINDS DEVELOPING LATE MONDAY
AND CONTINUING AT LEAST THROUGH MIDWEEK. PRECIPITATION CHANCES RETURN
FRIDAY AFTER A FEW DAYS OF DRY BUT COLD WEATHER.

&&

.SHORT TERM...TODAY THROUGH TUESDAY...IR IMAGERY THIS AFTERNOON SHOWS
AN UPPER LOW OVER WESTERN BRITISH COLUMBIA WITH A COLD FRONT SWINGING
SOUTH INTO NW WASHINGTON. AHEAD OF THE FRONT...PRECIP HAS SPREAD
ACROSS THE LOCAL FORECAST AREA WITH RATE OF UP TO ABOUT 0.10"/HR IN
THE HIGHER TERRAIN DUE TO OROGRAPHIC ENHANCEMENT. BASED ON
OBSERVATIONS...THERE HAS BEEN LITTLE MEASURABLE RAIN IN THE VALLEY
BUT IT SEEMS LIKELY THAT MOST LOCATIONS HAVE SEEN AT LEAST A TRACE OF
RAIN. RADAR CONTINUES TO SHOW SOME PRECIP MAKING IT INTO THE VALLEY
SO LOW LEVEL FLOW IS PROBABLY STILL A BIT SOUTHWESTERLY BUT SHOULD
VEER ALMOST DUE WEST SHORTLY...WHICH MAY SIGNIFICANTLY DECREASE
VALLEY POPS THROUGH TONIGHT. KEPT WITH THE NAM TREND FOR POPS WHICH
FAVORS THE HIGHER TERRAIN FOR PRECIP AND LEAVES THE WESTERN VALLEY
MOSTLY DRY AFTER SUNSET DUE TO THE RAIN SHADOW OF THE COAST RANGE.

NAM STILL SEEMS TO HAVE A GOOD HOLD ON THE NEAR-TERM SO FAVORED IT
FOR POPS...QPF...AND SNOW LEVELS WITH NOT A TON OF CHANGE TO ANY OF
THEM. ALMOST PURE WESTERLY FLOW OF AROUND 30 KT SHOULD KICK IN THIS
EVENING WHICH WILL BE THE MOST FAVORABLE PERIOD FOR HEAVIER SNOW IN
THE CASCADES. UPPED SNOW AMOUNT A BIT BUT STILL THINK IT WILL
REMAIN AT ADVISORY LEVELS. WITH SNOW LEVELS DROPPING TO 2000 FT
SUNDAY...CASCADE FOOTHILLS WILL GET IN ON THE SNOW ACTION BUT IT DOES
NOT LOOK LIKE ANY GIVEN 12 HR PERIOD OF SNOW WILL QUITE MEET ADVISORY
CRITERIA. WITH THAT BEING SAID...48 HR SNOWFALL TOTALS FOR SUNDAY AND
MONDAY IN THE NORTH OREGON CASCADE FOOTHILLS COULD BE AS HIGH AS 6 TO
8 INCHES ABOVE 2000 FT.

MODELS HAVE BEEN CONSISTENT WITH SECONDARY VORT MAX MOVING ACROSS THE
PAC NW SUNDAY NIGHT THROUGH MONDAY ALTHOUGH THE LATEST MODEL RUNS
HAVE MOVED THE ASSOCIATED WEAK SURFACE LOW A BIT WEST...MORE ALONG
THE COAST. MONDAY MORNING STILL LOOKS LIKE IT COULD BE INTERESTING
WITH COLDER AIR BEGINNING TO ARRIVE AT THE SAME TIME MODELS AGREE
POPS WILL CONTINUE. MODELS TRENDED EVER SO SLIGHTLY WARMER WITH
TEMPERATURES SUN NIGHT/MON MORN THOUGH WITH VALLEY LOWS NOW AROUND 35
DEG INSTEAD OF 33-34 DEG...BUT DUE TO UNCERTAINTY OF EXACT
VALUES...LEFT SLIGHT CHANCE SNOW IN FOR COOLER VALLEY LOCATIONS.
EITHER WAY...DO NOT EXPECT ANY SIGNIFICANT SNOW ACCUMULATIONS AT THE
VALLEY FLOOR.

MUCH COLDER AIR THEN SPILLS INTO THE REGION LATER MONDAY INTO MONDAY
NIGHT...WITH RAPID DRYING AND CLEARING. TEMPS MON NIGHT CONTINUE TO
TREND COLDER AND WILL BE THE COLDEST SO FAR THIS SEASON WITH SOME
UPPER TEENS POSSIBLE IN THE EASTERN VALLEY AND SINGLE DIGITS IN THE
HIGHER TERRAIN OF THE CASCADES. CHILLY NE FLOW WILL ADD AN EXTRA BITE
TO THE AIR WITH WIND CHILLS LIKELY IN THE TEENS OR EVEN SINGLE DIGITS
IN THE VALLEY BY TUE MORNING. WIND CHILLS IN THE CASCADES LOOKS LIKE
THEY`LL HAVE NO TROUBLE DROPPING BELOW ZERO AND IF MODELS CONTINUE TO
TREND COLDER...COULD SEE WIND CHILLS AT HIGHER ELEVATIONS APPROACH
WIND CHILL WARNING CRITERIA OF -20. BOWEN

.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...COLD...DRY WEATHER
CONTINUES THROUGH THE DAY WEDNESDAY...AS HIGH PRESSURE SITS OVER THE
AREA. ECMWF AND GFS ARE STARTING TO KEY IN ON A LOW PRESSURE SYSTEM
THAT WILL DIVE DOWN THE COAST LATE THIS WEEK...SHIFTING WINDS BACK
TO THE NORTHWEST AND BRINGING PRECIPITATION. THERE IS STILL
CONSIDERABLE UNCERTAINTY ON THE TIMING OF THIS SYSTEM...THOUGH. IF
THIS PANS OUT AS FORECAST RIGHT NOW...A CHANCE OF WINTRY MIX ALL
THE WAY TO THE FLOOR OF THE WILLAMETTE VALLEY IS POSSIBLE INITIALLY
THURSDAY NIGHT INTO EARLY FRIDAY. AS THE FRONT MOVES THROUGH
TEMPERATURES ARE STILL BELOW FREEZING...UNTIL ONSHORE WINDS AND
DAYTIME HEATING CAN BRING TEMPERATURES BACK ABOVE FREEZING LATE
FRIDAY MORNING OR AFTERNOON. IF THE FRONT IS SLOWER THAN FORECAST
AND MOVES THROUGH DURING THE DAY ON FRIDAY...TEMPERATURES WILL MORE
LIKELY BE ABOVE FREEZING KEEPING IT ALL RAIN. RAIN LOOKS TO CONTINUE
INTO SATURDAY. -MCCOY

&&

.AVIATION...LIGHT RAIN WITH A FRONTAL STORM SYSTEM THAT IS
CURRENTLY DROPPING SOUTHWARD ACROSS THE AREA WILL CONTINUE TO
BRING PERIODS OF MVFR CONDITIONS TO MOST TAF SITES LATE THIS
AFTERNOON AND EARLY EVENING. HOWEVER...MID LEVEL COLD ADVECTION
SHOULD ALLOW MANY LOCATIONS TO TURN VFR WITH ONLY AN OCCASIONAL
MVFR CONDITION EXPECTED TO OCCUR THIS EVENING AND OVERNIGHT. AS
THIS PROCESS WEAKENS TOWARDS 15Z SUNDAY...THERE IS A CHANCE AN
EXTENDED CLEAR PERIOD COULD ALLOW IFR TO LIFR FOG TO
FORM...PARTICULARLY AT KEUG. A WEAK LOW PRESSURE WILL DROP
SOUTHWARD ACROSS THE AREA AFTER 00Z MONDAY...BUT THIS SYSTEM COULD
RESULT IN VFR CONDITIONS DETERIORATING INTO AT LEAST THE MVFR
CATEGORY TOWARDS 00Z MONDAY.

KPDX AND APPROACHES...MVFR CONDITIONS THIS AFTERNOON SHOULD GIVE
WAY TO MAINLY VFR CONDITIONS THIS EVENING AND OVERNIGHT AS MID
LEVEL COLD ADVECTION DESTABILIZES THE LOWER ATMOSPHERE. AN
OCCASIONAL MVFR CIG WILL BE POSSIBLE...BUT THESE SHOULD BE SHORT
LIVED. ADDITIONAL FLIGHT RESTRICTIONS COULD CREEP INTO THE
TERMINAL TOWARDS 00Z MONDAY AS A WEAK LOW PRESSURE DROPS SOUTHWARD
WEST OF THE CASCADES. /NEUMAN

&&

.MARINE...A FRONT WILL DROP SOUTHWARD ACROSS THE WATERS THIS
EVENING...BRINGING GUSTY NORTHWEST WINDS AND HIGH SEAS TO THE
WATERS. WINDS AND SEAS SHOULD BE HIGHEST ACROSS THE SOUTH
WASHINGTON COASTAL WATERS...BUT LOOK TO REMAIN IN SOLID SMALL
CRAFT ADVISORY CRITERIA WITH GUSTS OF 25 TO 30 KT. SEAS OF MAY
APPROACH 15 FT ACROSS THE FAR NORTHERN WATERS...BUT SHOULD
GENERALLY TOP OUT IN THE 11 TO 13 FT RANGE TOWARDS THE CENTRAL
OREGON COAST. EXPECT SEAS TO START SUBSIDING SUNDAY AFTERNOON AND
SUNDAY NIGHT...LIKELY DROPPING BELOW 10 FT MONDAY MORNING.

A WEAK LOW PRESSURE MAY DEVELOP AND DRIFT SOUTHWARD ACROSS THE
INNER WATERS LATE SUNDAY NIGHT OR MONDAY MORNING...BUT IMPACTS TO
MARINE INTERESTS WILL BE FAIRLY MINIMAL INITIALLY. HOWEVER...AS
THE LOW PRESSURE DROPS SOUTH OF THE AREA...OFFSHORE PRESSURE
GRADIENTS WILL STRENGTHEN RAPIDLY. THIS WILL ALLOW GUSTY EAST TO
NORTHEAST WINDS TO DEVELOP ACROSS THE WATERS FOR THE SECOND HALF
OF MONDAY...LASTING THROUGH AT LEAST THE MIDDLE PART OF NEXT WEEK.
WITH NO MAJOR WESTERLY SWELLS...EXPECT SEAS TO RELAX CONSIDERABLY
DURING THIS TIME...BUT THEY COULD BECOME WIND DOMINATED DURING THE
PEAK OF THE EAST WINDS. THE PEAK IN EAST WINDS WILL LIKELY OCCUR
MONDAY NIGHT INTO TUESDAY. /NEUMAN

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 10 AM PST SUNDAY FOR CASCADES IN
     LANE COUNTY-NORTHERN OREGON CASCADES.

WA...WINTER WEATHER ADVISORY UNTIL 4 AM PST SUNDAY FOR SOUTH
     WASHINGTON CASCADES.

PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 10 PM PST SUNDAY FOR
     COASTAL WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR OUT 60
NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 9 AM PST MONDAY
     FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60
NM.

     SMALL CRAFT ADVISORY FOR WINDS UNTIL 6 PM PST SUNDAY FOR COASTAL
WATERS
     FROM CASCADE HEAD OR TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 1 PM PST
SUNDAY.

&&

$$

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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