Area Forecast Discussion
Issued by NWS Portland, OR

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000
FXUS66 KPQR 010453
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
853 PM PST SAT JAN 31 2015

.SYNOPSIS...HIGH CLOUDS ARE SPREADING ONSHORE THIS EVENING AHEAD OF
AN APPROACHING FRONTAL SYSTEM. MEANWHILE EASTERLY PRESSURE GRADIENTS
ARE DRIVING BLUSTERY EAST WINDS NEAR THE WESTERN COLUMBIA GORGE. THE
CLOUDS AND WIND WILL PROBABLY KEEP FOG OUT OF MOST OF THE PORTLAND
METRO AREA TONIGHT...BUT FOG AND LOW CLOUDS WILL PERSIST SALEM
SOUTHWARD. SOME LIGHT RAIN IS EXPECTED SUNDAY AS THE FIRST IN A
SERIES OF FRONTAL SYSTEMS MOVES ACROSS THE REGION. A STRONGER FRONT
IS EXPECTED MONDAY...LIKELY BRINGING MORE RAIN AND SOME BREEZY
CONDITIONS BOTH COAST AND INLAND...AS WELL AS A SLIGHT CHANCE OF
THUNDER. COMPUTER MODELS DIVERGE ON WHETHER OR NOT THE MIDWEEK PERIOD
WILL BE DRY OR RAINY...BUT COME BACK INTO AGREEMENT THAT THE END OF
THE WEEK WILL BE WET. SNOW LEVELS WILL LIKELY REMAIN TOO HIGH MUCH OF
THE WEEK FOR APPRECIABLE IMPROVEMENT IN THE CASCADE SNOWPACK.

&&

.SHORT TERM...TONIGHT THROUGH MONDAY NIGHT...EAST WINDS CONTINUE TO
RAMP UP THROUGH THE COLUMBIA GORGE...WITH A RECENT GUST UP TO 64 MPH
IN CORBETT AND EARLIER GUSTS TO 75 MPH AT THE VISTA HOUSE ON CROWN
POINT. THE BRISK EAST WINDS ARE BEING DRIVEN BY -7.6 MB GRADIENTS
KTTD-KDLS. COLD POOL HIGH PRESSURE REMAINS FAIRLY STRONG EAST OF THE
CASCADES...WITH STRATUS REMAINING WIDESPREAD IN THE COLUMBIA BASIN.
MEANWHILE AN APPROACHING WEAK FRONTAL SYSTEM IS LOWERING PRESSURE
OFFSHORE... RESULTING IN THE INCREASING GRADIENTS. AS USUAL THE 00Z
NAM UNDER- ANALYZES THE GRADIENT AND APPEARS TO WEAKEN THE EASTSIDE
HIGH TOO QUICKLY. THUS EXPECT A BRISK AND CHILLY NIGHT TONIGHT FOR AT
LEAST THE EAST PDX/VUO METRO AND WEST GORGE...WITH FOG LIKELY HAVING
A HARD TIME FORMING NEARBY.

ELSEWHERE...FOG AND LOW CLOUDS REMAIN STUBBORN IN THE WILLAMETTE
VALLEY SOUTH OF SALEM AND ALONG THE I-5 CORRIDOR NORTH OF ABOUT
KALAMA THROUGH THE LEWIS COUNTY LINE. EXPECT THAT HIGH CLOUDS WILL
LIMIT THE RADIATIONAL COOLING POTENTIAL TONIGHT...KEEPING FOG FROM
BEING AS DENSE AS IT WAS LAST NIGHT.

THE MAIN CHANGE TO THE FORECAST THIS EVENING WAS TO ALLOW TEMPS TO
REMAIN COLD ENOUGH FOR LIGHT SNOW SUNDAY MORNING IN EASTERN SKAMANIA
COUNTY AND THE EAST SIDE OF MOUNT HOOD...AS THE EASTERLY GRADIENTS
APPEAR TO BE JAMMING PLENTY OF EASTSIDE COLD AIR INTO THESE AREAS. IN
THE PAST HOUR...BUCK CREEK RAWS NEAR TROUT LAKE WAS 29 DEGREES... AND
A COUPLE ELEVATED SITES NEAR THE GORGE WERE IN THE UPPER 20S.
PRECIPITATION WILL BE RATHER LIGHT AS A WEAK FRONT MOVES ONSHORE
SUNDAY...SO ANY ACCUMULATIONS SHOULD REMAIN AROUND AN INCH OR SO.
TEMPS WILL PROBABLY HANG JUST ABOVE FREEZING IN THE HOOD RIVER
VALLEY...SO SIGNIFICANT WINTRY PRECIPITATION IS NOT LIKELY THERE OR
ON THE WESTERN OR CENTRAL COLUMBIA GORGE FLOOR.

MODELS SHOW GOOD AGREEMENT IN BRINGING A SHARPER AND MORE DYNAMIC
COLD FRONT IN ON MONDAY. AFTER A PERIOD OF STRATIFORM RAIN EARLY
MONDAY...IT APPEARS THERE WILL BE A PERIOD OF DECENT SOUTHERLY FLOW
ALONG THE COAST AND THROUGH THE WILLAMETTE VALLEY MIDDAY MONDAY AS
THE FRONT APPROACHES. THIS SHOULD FINALLY BREAK THROUGH VALLEY
INVERSIONS AND WARM UP THE LOWLANDS CONSIDERABLY...JUST IN TIME FOR A
SHARP COLD FRONT TO MOVE THROUGH. 00Z NAM BUFR SOUNDINGS SHOW THE
POTENTIAL FOR SOME INSTABILITY...WITH CAPE OF 400-800 J/KG JUST ABOVE
LOW-LEVEL INVERSIONS. WITH SOUTHERLY FLOW PUNCHING IN IT APPEARS THE
NAM IS A BIT TOO STUBBORN WITH THE INVERSIONS MONDAY AFTERNOON AND
THE DOOR MAY OPEN UP FOR SOME SURFACE-BASED CONVECTION WITH THE COLD
FRONT MONDAY AFTERNOON. THE SOUNDINGS ALSO SHOW DECENT DIRECTIONAL
SHEAR WITHIN THE UNSTABLE LAYER. THEREFORE WE ADDED A SLIGHT CHANCE
OF THUNDER MONDAY AFTERNOON ACCORDINGLY...COULD BE AN INTERESTING DAY
IF ALL COMES TOGETHER.

AS MENTIONED ABOVE...THE MONDAY FRONT WILL BE A BIT STRONGER THAN THE
SUNDAY SYSTEM...AND WILL PRODUCE SLIGHTLY GUSTIER WINDS. AT THIS
POINT IT APPEARS WINDS WILL TOP OUT AROUND 45 MPH ALONG THE COAST AND
30 MPH FOR THE INLAND VALLEYS. HOWEVER A STRONG WESTERLY PUSH BEHIND
THE FRONT WILL MAKE IT GUSTY IN THE CASCADES AS WELL. RAINFALL TOTALS
WILL BE HIGHER AS WELL...EXPECT 0.5 TO 0.75 INCH OF RAIN FOR THE
HIGHER TERRAIN MONDAY MORNING THROUGH MONDAY AFTERNOON WITH BETWEEN
0.25-0.50 INCH FOR THE LOW LANDS.

SNOW LEVELS WILL BE BETWEEN 5500 AND 6500 FEET MONDAY WITH POSSIBLY 6
TO 8 INCHES OF NEW SNOW FOR THE VERY HIGH ELEVATIONS OF THE SOUTH
WASHINGTON AND NORTHERN OREGON CASCADES. SNOW LEVELS WILL LOWER TO
NEAR THE CASCADE PASSES MONDAY NIGHT INTO TUESDAY MORNING. WEAKENING
POST-FRONTAL SHOWERS MAY BRING A DUSTING OF SNOW TO THE CASCADE
PASSES OVERNIGHT MONDAY AND TUESDAY MORNING WITH SPOTTY 1 TO 3 INCHES
OF NEW SNOW ABOVE 5000 FEET.  WEAGLE/TJ

LONG TERM...TUESDAY THROUGH FRIDAY NIGHT...MODELS BEGIN TO DIVERGE
TUESDAY WITH THE GFS FORECASTING AN UPPER RIDGE TO RETURN OVER THE
PACIFIC NW AND THE ECMWF FORECASTING A WEAKER RIDGE FURTHER
OFFSHORE...AND A SHORTWAVE TROUGH IMPACTING THE REGION. THERE IS A
POSSIBILITY THAT BOTH OF THESE MODELS ARE OVERDOING THEIR
FORECASTS...WITH THE GFS RIDGE AND THE ECMWF TROUGH BEING TOO STRONG.
THE GFS SOLUTION WOULD RESULT IN DRY WEATHER FOR NW OREGON TUESDAY
AND WEDNESDAY WHEREAS THE ECMWF WOULD RESULT IN WET WEATHER. THINK
THERE WILL BE A BIT OF BOTH AND EXPECT A WARM FRONT WILL BRING VERY
LIGHT RAIN TO THE REGION TUESDAY WITH DRYING FOR WEDNESDAY. THIS PANS
OUT AS A LOW CONFIDENCE CHANCE OF RAIN FORECAST.

THE MODELS ARE THEN IN SURPRISING AGREEMENT THAT A PERIOD OF WET
WEATHER WILL IMPACT THE REGION THURSDAY AND FRIDAY...AND POSSIBLY
INTO NEXT WEEKEND AS A SWATH OF SUBTROPICAL MOISTURE COMBINED WITH A
SERIES OF ATMOSPHERIC WAVES SETS UP OVER THE NE PACIFIC. THIS WEATHER
PATTERN WILL LIKELY BRING A SUBSTANTIAL AMOUNT OF RAIN TO  PARTS OF
THE PACIFIC NORTHWEST...BUT WOULD LIKE TO SEE THE FIRST WEATHER
SYSTEMS THIS WEEKEND AND EARLY NEXT WEEK PAN OUT BEFORE EVEN TRYING
TO DETERMINE WHERE THE HEAVIEST RAIN WILL BE. TJ

&&

.AVIATION...LIFR CIGS/VSBYS AT KEUG WILL CONTINUE FOR MOST OF THE
NIGHT TONIGHT AS AN OFFSHORE COLD FRONT WORKS TOWARD THE REGION.
INCREASING CLOUDS SHOULD LIMIT THE FOG DEVELOPMENT MOST AREAS.
OTHERWISE...CIGS WILL GRADUALLY LOWER OVERNIGHT THROUGH TOMORROW
MORNING WITH RAIN DEVELOPING AROUND 14Z AT THE COAST AND CLOSER TO
16Z FOR THE I-5 CENTRIC TERMINALS. THE FRONT LOOKS TO CROSS THE
COAST NEAR 20Z AND AROUND 23Z INLAND. EXPECT SHOWERS AFTER THE
FRONT BUT NOT PARTICULARLY STRONG AND CIGS LIFTING TO MVFR EXCEPT
FOR KEUG WHERE THEY MAY REMAIN STUCK IFR BUT WITH IMPROVED
VISIBILITY FOR SUNDAY AFTERNOON AND EVENING.

KPDX AND APPROACHES...VFR CONDITIONS WILL PREVAIL TONIGHT WITH
GUSTY EAST WINDS. STRONGEST GUSTS WILL BE NEAREST THE GORGE. MID
AND HIGH CLOUDS INCREASE OVERNIGHT WITH CIGS FALLING FROM 100 TO
050 AROUND 16Z SUN ALONG WITH RAIN DEVELOPING. MAY SEE IFR CIGS
WORK SOUTH ALONG THE I-5 CORRIDOR FROM THE KKLS AREA TOWARD KPDX
BUT EASTERLY OUTFLOW FROM THE GORGE SHOULD KEEP IT AS AN IFR
STRATUS DECK IF IT ARRIVES AT ALL. RAIN PICKS UP AROUND 16Z AND
CIGS FALL TO 025. EXPECT FRONTAL PASSAGE AND A TRANSITION TO
SHOWERS NEAR 23Z. /JBONK
&&

.MARINE...MINIMAL CHANGES. HAVE AGREED THE WINDS ON SUNDAY ARE
VERY MARGINAL FOR JUSTIFYING A SMALL CRAFT ADVISORY SO WILL HOLD
OFF ON ISSUING ONE AT THIS TIME. BULK OF THE PREVIOUS DISCUSSION
FOLLOWS. /JBONK

PREVIOUS DISCUSSION...THE FIRST IN A SERIES OF PROGRESSIVELY
STRONGER FRONTAL SYSTEMS CAN BE SEEN APPROACHING THE REGION THIS
AFTERNOON...AND WILL MOVE THROUGH SUNDAY MORNING. THIS FIRST FRONT
ON SUNDAY BRINGS THE POSSIBILITY OF SOME SMALL CRAFT ADVISORY
GUSTS ABOVE 20 KTS WHILE BRINGING SEAS UP TO AROUND 8 FT. THE
SECOND FRONTAL SYSTEM MOVES THROUGH ON MONDAY...BRINGING SOLID
SMALL CRAFT ADVISORY WINDS WITH GUSTS 30 TO 35 KTS LIKELY. STRONG
WINDS WILL RAMP UP EARLY MONDAY MORNING AND PERSIST THROUGH THE
DAY UNTIL WINDS EASE BEHIND THE FRONT LATE MONDAY NIGHT OR EARLY
TUESDAY. THIS SYSTEM WILL ALSO BRING SEAS UP TO AROUND 12 TO 13 FT
ON MONDAY. CONFIDENCE IS INCREASING FOR AN EVEN STRONGER SYSTEM
THURSDAY OR FRIDAY WHICH COULD GENERATE SOUTHERLY GALES AND BRING
SEAS UP TO NEAR 20 FT. /27

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...NONE.

&&

$$

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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