Area Forecast Discussion
Issued by NWS Portland, OR

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000
FXUS66 KPQR 281126
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
326 AM PST FRI NOV 28 2014

.SYNOPSIS...A STALLED BAROCLINIC ZONE OVER SOUTH-CENTRAL OREGON
HAS BEEN REACTIVATED THIS MORNING BY AN APPROACHING UPPER LEVEL
DISTURBANCE...CAUSING RAIN TO SLOWLY FILL BACK ACROSS THE FORECAST
REGION. A WELL-DEFINED COLD FRONT WILL MOVE SOUTHEAST ACROSS THE
REGION TONIGHT. THERE WILL BE A SHARP TEMPERATURE DROP WITH THE
PASSAGE OF THIS COLD FRONT...WITH SNOW LEVELS QUICKLY LOWERING BEHIND
THE FRONT. EXPECT A QUICK BURST OF ACCUMULATING SNOWFALL IN THE
HIGHER CASCADE PASSES AS THE FRONT MOVES THROUGH. MIXED RAIN/SNOW
SHOWERS ARE THEN EXPECTED IN THE LOWLANDS OVERNIGHT AND SAT AS AN
UPPER TROUGH PASSES THROUGH...WITH LITTLE TO NO ACCUMULATION
EXPECTED. HIGH PRESSURE WILL SETTLE IN EAST OF THE CASCADES SATURDAY
NIGHT AND SUNDAY... BRINGING STRONG EAST WINDS THROUGH THE GORGE AND
ACROSS THE PORTLAND METRO AREA. A SYSTEM COMING UP FROM THE SOUTH MAY
ATTEMPT TO SPREAD MOISTURE UP OVER THE COLD AIR ON MON...BUT FCST
DETAILS DURING THIS TIME REMAIN HIGHLY UNCERTAIN.

&&

.SHORT TERM...TODAY THROUGH MONDAY...A STALLED BAROCLINIC ZONE OVER
SOUTH-CENTRAL OREGON IS BEING REACTIVATED BY AN APPROACHING UPPER
LEVEL DISTURBANCE OVER THE NE PAC. AS A RESULT...RAIN IS FILLING BACK
IN ACROSS NW OREGON AND SW WASHINGTON THIS MORNING. EXPECT A MILD AND
WET DAY AHEAD...WITH LIGHT TO MODERATE STEADY RAIN FALLING FOR MOST
OF THE DAY WITH SNOW LEVELS REMAINING ABOVE 6000 FT.
MEANWHILE...ANOTHER BAROCLINIC ZONE DRAPED OVER SOUTHERN BRITISH
COLUMBIA WILL BE DRIVEN INTO WA TODAY AS A COLD FRONT BY A POSITIVELY
TILTED UPPER LEVEL TROUGH FROM THE NORTH. THIS COLD FRONT WILL THEN
MOVE THROUGH SW WASHINGTON AND NW OREGON TONIGHT. THERE WILL BE A
PERIOD OF HEAVIER PRECIPITATION WITH THE FRONTAL PASSAGE...ALONG WITH
THE ARRIVAL OF A SIGNIFICANTLY COLDER AIR MASS BEHIND THE FRONT. THIS
COLD FRONT WILL BE QUITE SHARP BY PAC NW STANDARDS...WITH THE FCST
MODELS SHOWING ABOUT AN 8 DEG CELSIUS DROP OVER A 6 HR PERIOD AT 850
MB WITH THE FRONTAL PASSAGE. PRECIPITATION WILL START OUT AS ALL RAIN
BELOW 6000 FT...BUT SNOW LEVELS WILL RAPIDLY PLUMMET ON THE BACK SIDE
OF THE FRONT.X1AEXPECT A QUICK BURST OF ACCUMULATION SNOW FOR THE
HIGHER CASCADE PASSES WITH THE FRONT. IT CURRENTLY LOOKS LIKE AMOUNTS
WILL REMAIN BELOW ADVISORY THRESHOLDS...SO WILL NOT ISSUE ANY WINTER
WEATHER PRODUCTS AT THIS TIME. HOWEVER...A SHORT PERIOD OF HEAVY SNOW
ON THE BACK SIDE OF THE FRONT MAY MAKE TRAVEL OVER THE PASSES
TREACHEROUS FOR A TIME TONIGHT.

PRECIPITATION WILL QUICKLY TAPER OFF TO SHOWERS BEHIND THE FRONT
OVERNIGHT INTO SAT MORNING. EXPECT PLENTY OF SHOWERS AROUND THROUGH
SAT AFTERNOON AS THE POSITIVELY TILTED UPPER TROUGH MOVES THROUGH THE
REGION. THE LATEST FCST MODEL RUNS CONTINUE TO INDICATE 850MB TEMPS
WILL FALL INTO THE -6C TO -8 RANGE...WHICH WILL OFTEN SUPPORT A
RAIN/SNOW MIX DOWN TO NEAR THE VALLEY FLOOR. QPF AMOUNTS ON SAT ARE
NOT EXPECTED TO BE VERY IMPRESSIVE...SO IT DOESN`T LOOK LIKE THERE
WILL BE ANY MAJOR TRAVEL IMPACTS. HOWEVER...IT IS NOT OUT OF THE
QUESTION THAT A FEW HEAVIER SHOWERS COULD PRODUCE LOCALIZED LIGHT
SNOWFALL ACCUMULATIONS NEAR THE VALLEY FLOOR...OR ALONG THE S WA OR N
OR COAST.

SHOWER ACTIVITY WILL DROP OFF SIGNIFICANT SAT NIGHT BEHIND THE
DEPARTING UPPER LEVEL TROUGH. WE WILL THEN TRANSITION TO A
DRY...COLD...AND GUSTY OFFSHORE FLOW PATTERN FROM SAT NIGHT THROUGH
SUN NIGHT AS VERY COLD ARCTIC AIR MASS AND ASSOCIATED SURFACE HIGH
PRES MOVES INTO THE COLUMBIA BASIN EAST OF THE CASCADES. HIGH
RESOLUTION FCST MODELS CONTINUE TO SUGGEST KTTD-KDLS PRESSURE
GRADIENTS WILL GET TO -10 MB OR POSSIBLY STRONGER. THIS WOULD BE
ENOUGH FOR EAST WINDS GUSTING 60-70 MPH THROUGH THE GORGE...AND 40-45
MPH GUSTS IN THE PORTLAND METRO AREA. IF MODELS CONTINUE THIS
TREND...A WIND ADVISORY MAY EVENTUALLY BE NEEDED FOR THE
PORTLAND/VANCOUVER METRO. TEMPERATURES WILL BE WELL BELOW NORMAL
SAT/SUN...WITH HIGHS STUCK IN THE 30S IN AND NEAR THE GORGE AND 40S
MOST LOWLAND LOCATIONS ELSEWHERE.  PYLE

.LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...FCST CONFIDENCE
DECREASES CONSIDERABLY GOING INTO EARLY NEXT WEEK. A CLOSED LOW PRES
SYSTEM IS EXPECTED TO SET UP WELL OFFSHORE TO OUR SW ON SUN AND SUN
NIGHT. THE PAST SEVERAL RUNS OF THE GFS MODEL HAVE SUGGESTED THAT THE
LOW WOULD PUSH CLOSE ENOUGH TO THE COAST TO SPREAD SOME MOISTURE AND
LIGHT PRECIPITATION ONSHORE BEGINNING MON MORNING. MEANWHILE...THE
ECMWF AND CANADIAN MODELS HAVE BEEN TENDING TO KEEP THE LOW FURTHER
OFFSHORE...WITH MOSTLY DRY WEATHER REMAINING IN CONTROL OVER THE PAC
NW THROUGH MIDWEEK. HOWEVER...THE 00Z ECMWF AND TO SOME EXTENT THE
00Z NAM AS WELL NOW APPEAR TO BE TRENDING TOWARD THE GFS
SOLUTION...BRINGING SOME MOISTURE IN FROM THE SOUTH ON MON. AN
EASTERLY GRADIENT PERSISTS THROUGH THE GORGE...SO ANY PRECIP THAT
DOES FALL COULD BRING FREEZING RAIN POTENTIAL FOR THE GORGE...AND
ALSO POTENTIALLY INTO THE WILLAMETTE VALLEY. WILL NEED TO MONITOR THE
FCST MODEL TRENDS CLOSELY OVER THE NEXT COUPLE OF DAYS. A NORTHERN
STREAM SHORTWAVE IS MODELED TO PUSH THROUGH LATER MON NIGHT...WHICH
SHOULD HELP TO ERODE THE EASTERLY LOW LEVEL GRADIENT AND BRING THE
TRANSITION TO A MILDER AIR MASS. CHANCES FOR PRECIPITATION WILL
REMAIN THROUGH MIDWEEK AS THE OFFSHORE CLOSED LOW SLOWLY PUSHES
TOWARD THE COAST...BUT CONFIDENCE IN THE DETAILS ARE VERY LOW AT THIS
TIME. PYLE

&&

.AVIATION...A FRONTAL BOUNDARY CONTINUES TO LINGER FROM THE SOUTH
OREGON COAST NORTHEAST INTO NORTHEAST OREGON...IMPACTING THE
SOUTHEAST PORTION OF NORTHWEST OREGON. TO THE NORTH OF A FRONT A
HANDFUL OF SHOWERS ARE MOVING THROUGH. ANOTHER MORE ROBUST COLD
FRONT WAS ALONG THE WASHINGTON COAST EARLY THIS MORNING AND WILL
MOVE INTO SOUTHWEST WASHINGTON AND FAR NORTHWEST OREGON LATER THIS
MORNING AND EARLY THIS AFTERNOON FOR MORE SUBSTANTIAL STEADIER
RAIN...THEN ACROSS THE REMAINDER OF NORTHWEST OREGON THIS
AFTERNOON AND EVENING. THE NET RESULT WILL BE CONTINUED RATHER
DETERIORATED CONDITIONS OVER THE AREA. THE COAST WILL SEE MOSTLY
MVFR CONDITIONS WITH POSSIBLE IFR CONDITIONS AS THE NORTHERN FRONT
DROPS SOUTH INTO THE AREA. INLAND WILL SEE A MIXTURE OF MVFR AND
LOW VFR CONDITIONS. PRECIPITATION WILL TURN SHOWERY FROM THE
NORTHWEST FRIDAY NIGHT INTO SATURDAY MORNING WITH SOME VFR
CONDITIONS TRYING TO DEVELOP...AND DRAMATICALLY LOWER SNOW LEVELS
MAY ALLOW SOME MIXTURE OF RAIN AND SNOW SHOWERS TO REACH LOW
ELEVATIONS BY SATURDAY MORNING.

KPDX AND APPROACHES...A MIX OF MVFR AND LOW VFR CONDITIONS ARE
EXPECTED AT THE TERMINAL AND APPROACHES WITH CIGS 2500 TO 3500 FT
RANGE. AS A COLD FRONT MOVES SOUTH THROUGH THE AREA MID DAY TODAY
CIGS MAY TREND MORE TO THE MVFR CATEGORY. SOUTH WINDS WILL
CONTINUE MUCH OF TODAY...SHIFTING TO W-NW BEHIND THE FRONT BETWEEN
4 AND 7 PM THIS EVENING. PT
&&

.MARINE...LATEST MODEL GUIDANCE AND OBSERVATIONS CONTINUE TO
SUGGEST GUSTS TO 25 KT AT TIMES INTO SATURDAY MORNING. THERE MAY
BE SHORT PERIODS OF SUB ADVISORY WIND SPEEDS THROUGH SATURDAY
MORNING...BUT BELIEVE THIS WILL BE THE EXCEPTION INSTEAD OF THE
RULE. ONE FRONTAL BOUNDARY REMAINS DRAPED FROM SOUTHWEST TO
NORTHEAST FROM THE SOUTHERN OREGON WATERS INLAND INTO NORTHEAST
OREGON EARLY THIS MORNING. A MORE ROBUST COLD FRONT IS ALONG THE
WASHINGTON COAST AND WILL MOVE SOUTH THROUGH THE COASTAL WATERS
TODAY AND EARLY THIS EVENING FOR CONTINUED SMALL CRAFT ADVISORY
WIND. THE WIND WILL SWITCH TO THE NORTHWEST BEHIND THIS FRONT. THE
NORTHWEST WINDS WILL EASE ON SATURDAY...THEN OFFSHORE GAP ENHANCED
EAST WINDS WILL DEVELOP SATURDAY NIGHT AND SUNDAY...LIKELY
EXCEEDING SMALL CRAFT ADVISORY CRITERIA. THE OFFSHORE WIND
CONTINUES INTO EARLY NEXT WEEK...BUT FAVOR THE ECMWF WIND PATTERN.

SEAS WILL BE IN THE 10 TO 12 FOOT RANGE THIS MORNING. SEAS FALL
BELOW 10 FEET IN THE CENTRAL OREGON COAST WATERS TONIGHT...BUT NOT
IN THE NORTHERN WATERS UNTIL LATE SATURDAY OR SATURDAY EVENING.
SEAS IN THE CENTRAL WATERS MAY BRIEFLY REACH 10 FT AGAIN FOR A
TIME ON SATURDAY BEFORE FALLING BELOW 10 FT AGAIN SATURDAY NIGHT.
THE OFFSHORE FLOW LATER THIS WEEKEND WILL DECREASE WAVE HEIGHT...
BUT RESULT IN VERY CHOPPY CONDITIONS. PT
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 8 AM PST SATURDAY FOR
     COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT
     60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 7 PM PST
     SATURDAY FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO
     CASCADE HEAD OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 10 PM PST THIS
     EVENING FOR COASTAL WATERS FROM CASCADE HEAD OR TO FLORENCE
     OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL
     4 AM PST SATURDAY.

&&

$$

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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