189
FXUS66 KPQR 020540 AAA
AFDPQR
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
940 PM PST THU DEC 1 2022
UPDATED AVIATION AND WWA SUMMARY...
SYNOPSIS
A COOL SEASONABLE SERIES OF SYSTEMS WILL CONTINUE
TO PUSH INLAND OVER THE NEXT SEVERAL DAYS. EACH OF THESE
DISTURBANCES WILL BRING PRECIPITATION WITH A MIX OF
PRECIPITATION. OVERALL, CONFIDENCE IS FAIRLY LOW IN THE SENSIBLE
WEATHER IN MID-RANGE FORECAST DUE TO VARIABLE AND SENSITIVE
THRESHOLDS FOR WINTER WEATHER. TRENDING TOWARDS A DRIER SOLUTION
FOR NEXT WEEK.
SHORT TERM /THROUGH SUNDAY NIGHT/
THE FIRST DAY OF
METEOROLOGICAL WINTER HAS BROUGHT QUITE THE GRAB BAG OF WEATHER
TYPES RANGING FROM SNOW, TO RAIN, TO THUNDER STORMS. RADAR AND
SATELLITE IMAGERY SHOW THAT THE LOW PRESSURE SYSTEM WHICH
BROUGHT THE HEAVY RAIN AND SNOW YESTERDAY HAS SHIFTED INLAND TO
NORTHEAST OF THE CASCADES. THIS LOW SPUN NEARLY STATIONARY OVER
THE NORTH OREGON AND SOUTH WASHINGTON COAST THROUGH AROUND 20Z
THURSDAY WHICH PROPAGATED SEVERAL ROUNDS OF SHOWERS OVER THE
NORTHERN PORTIONS OF THE FORECAST AREA. EVEN WITH TEMPERATURES
SITTING ABOVE FREEZING, WITH THESE PASSING SHOWERS, WET BULB
TEMPERATURES DROPPED WHICH ALLOWED FOR COOLING OF THE
ATMOSPHERE. ALL OF WHICH IS ENOUGH TO CAUSE PRECIPITATION TO
FALL AS SNOW - ALBEIT FAIRLY WET IN NATURE. OBSERVED ISOLATED
DUSTINGS OF SNOW THROUGHOUT MOST GEOGRAPHIC REGIONS, BUT DUE TO
THE SHOWERY NATURE WAS NOT WIDESPREAD OVER HEAVY. AREAS ABOVE
500 FT ALONG THE COAST RANGE, AND IN COLUMBIA, COWLITZ, AND
PACIFIC COUNTY ALL RECEIVED ACCUMULATING SNOW. WEB CAMERAS STILL
SHOW SOME ACCUMULATED SNOW ALONG THE SIDES OF ROADS. THE
CASCADES AND FOOTHILLS SAW SNOWFALL DWINDLE THIS AFTERNOON WITH
UP TO 4 INCHES OF ADDITIONAL SNOWFALL ACCUMULATED. LATER THIS
AFTERNOON, MODELS ARE SUGGESTING THE PROPAGATION OF ANOTHER
SHORTWAVE TROUGH WHICH MAY AMPLIFY SHOWERS AND INCREASE THE
INTENSITY AND FREQUENCY OF SHOWERS. FROM A NUMERICAL MODEL
PERSPECTIVE, HI-RESOLUTION MODELS HAVE HAD A GOOD HANDLE ON THE
LOCATION AND ACCUMULATIONS OF PRECIPITATION BUT THE NAM HAS
VERIFIED THE BEST WITH THIS PASSING LOW. HAVE DECIDED TO TREND
TOWARDS A NAM BASED SOLUTION IN THE SHORT TERM FOR QPF. THERE IS
A CHANCE THAT A FEW MORE INCHES OF SNOW ARE POSSIBLE ALONG THE
CASCADES ABOVE 1000 FT SO HAVE DECIDED TO MAINTAIN THE WINTER
STORM WARNING UNTIL 06Z FRIDAY AS TO FINISH UP THIS SYSTEM.
ON FRIDAY, CONDITIONS ARE A BIT MORE VARIABLE AND THERE IS STILL
QUITE A BIT OF UNCERTAINTY WHICH STEMS FROM THE SHIFTING OF A
BROAD LOW PRESSURE SYSTEM DROPPING DOWN FROM THE GULF OF ALASKA
AND A TRANSIENT WEAK HIGH. BECAUSE OF THIS, PRECIPITATION WILL
BE LESS WIDESPREAD AND POPS HAVE DECREASED THROUGHOUT MUCH OF
THE FORECAST AREA ASIDE FROM THE COASTLINE. WITH THIS SHIFT,
TEMPERATURES ARE NOT EXPECTED TO DIP AS LOW AS THEY WERE
PREVIOUSLY FORECAST TO BE AND THUS, SNOW LEVELS HAVE RISEN
SLIGHTLY. MODELED WET BULB 0C HEIGHTS ARE VARIABLE BETWEEN
MODELS WITH SNOW LEVELS RANGING FROM 600-800 FT SOUTH OF SALEM,
WHILE THE ECMWF AND CANADIAN ARE HIGHER THAN 1000 FT FRIDAY
MORNING, RISING TO GREATER THAN 2000 FT IN THE AFTERNOON.
DECIDED TO SPLIT THE DIFFERENCE DURING THIS BRIEF BREAK BETWEEN
SYSTEMS. GIVEN THOSE SNOW LEVELS, MOST AREAS WILL SEE ANY
PRECIPITATION FALLING AS RAIN, WHILE THE MOUNTAINS AND SOME
AREAS OF THE COAST RANGE CAN EXPECT VERY LIGHT SNOW.
THE LOW PREVIOUSLY MENTIONED WILL BE THE MAIN SENSIBLE WEATHER
MAKER THROUGH THE WEEKEND. THIS LOW HAS SHIFTED TO BE MORE
OFFSHORE THAN PREVIOUSLY FORECAST WHICH WILL KEEP MUCH OF THE
PRECIPITATION CONCENTRATED TO THE COAST WITH ISOLATED SCATTERED
SHOWERS POSSIBLE INLAND. THE 90TH PERCENTILE FOR PRECIPITATION
IS AROUND 0.25 THROUGH THE WILLAMETTE VALLEY SLIGHTLY LOWER FOR
THE CASCADES. THIS REPRESENTS THE "WORST CASE SCENARIO" FOR
SATURDAY. THIS IS A TYPICAL RAINFALL FOR THIS TIME OF YEAR SO
THERE AREN'T ANY CONCERNS. THE ONE AREA WE WILL CONTINUE TO
WATCH IS ON SATURDAY MORNING AS SNOW LEVELS REDUCE AND AN EAST
WIND KICKS IN. THE FORECAST PRESSURE GRADIENT FROM KTTD TO KDLS
(A GOOD PROXY FOR EASTERLY WINDS THROUGH THE GORGE AND PASSES)
RANGES FROM AROUND -4 TO -10 MB WITH THE -10 BEING THE MOST
INTENSE GRADIENT AND THUS WINDIEST SOLUTION. THIS SUGGESTS THAT
WE COULD SEE ANOTHER ROUND OF INCREASED EASTERLY WINDS. THE GFS
IS TRENDING ON THE HIGH SIDE FOR WIND SPEEDS AND THE OVERALL
PATTERN IS BEGINNING TO TAKE ON MORE OF A DOWNSLOPING PATTERN
VS A GAP WIND. THUS, IF THERE ARE ANY STRONGER WINDS ALOFT,
THOSE COULD MIX DOWN TO THE SURFACE. NBM 90TH PERCENTILE WIND
SPEEDS THROUGH THE COLUMBIA RIVER GORGE AROUND THREE CORNER ROCK
ARE AROUND 70 MPH, THE 50TH PERCENTILE AROUND 50 MPH, AND THE
10TH PERCENTILE AROUND 35 MPH. THIS IS SLIGHTLY STRONGER THAN
THE WEEK OF EASTERLY WINDS THAT WERE EXPERIENCED A FEW WEEKS
AGO, BUT ARE ONLY EXPECTED FOR TWO DAYS. BUT, WHILE WINDS ARE
NOT EXCEEDINGLY STRONG, THE IMPACT OF USHERING IN COLD AIR MAY
BE. WITH THE COLD AIR FILTERING INTO THE WILLAMETTE VALLEY FROM
BOTH THE GORGE AND THE CASCADE VALLEYS, WE MAY SEE A POOL OF
COLD AIR AT THE SURFACE.
THIS LOW APPEARS TO START PROGRESSING INLAND LATE SATURDAY INTO
SUNDAY MOVING FROM SOUTHERN OREGON NORTHWARD. IF THIS
PRECIPITATION OCCURS DURING THE COLDER PART OF THE NIGHT THERE
IS A CHANCE THAT IT COULD INTERSECT WITH THE COLD AIR AT THE
SURFACE AND THUS, SLIGHT CHANCES FOR FREEZING RAIN. AS IT
STANDS, THERE IS AROUND A 10-20% CHANCE FOR FREEZING RAIN
AMOUNTING TO A LIGHT GLAZE, BUT THIS EQUALLY MEANS THAT THERE IS
AN 80-90% CHANCE THAT IT WILL NOT HAPPEN. WE WILL CONTINUE TO
MONITOR AS IT WILL GREATLY DEPEND ON THE TIMING OF THE
PRECIPITATION TO WHETHER OR NOT TEMPERATURES REACH FREEZING
AFTER A DEEP ENOUGH MELTING LAYER.-MUESSLE
LONG TERM /MONDAY THROUGH WEDNESDAY/
THE OVERALL WEATHER
PATTERN EARLY NEXT WEEK WILL BEGIN WITH A TALL RIDGE EXTENDING
FROM THE PACIFIC NEAR HAWAII ALL THE WAY UP INTO THE ARCTIC
OCEAN. THIS RIDGE WILL BE SANDWICHED BETWEEN TWO LONGWAVE
TROUGHS...ONE MOVING OFF OF SIBERIA AND THE OTHER OVER HUDSON
BAY. ONE SHORTWAVE TROUGH SPINNING OFF OF THE HUDSON BAY LOW IS
THE LOW THAT HAD BROUGHT WEATHER TO THE FORECAST AREA FOR FRIDAY
INTO THE WEEKEND, AND WILL HAVE SLID SOUTH OVER NORTHERN
CALIFORNIA BY MONDAY. NORTHWESTERLY FLOW OVER THE AREA WILL KEEP
IN COOLER THAN AVERAGE TEMPERATURES, AS WELL AS A SLIGHT CHANCE
FOR SHOWERS WITH ANY REMAINING MOISTURE. ENERGY SPINNING AROUND
THE TWO UPPER LOWS WILL SLOWLY PROPEL THEM TOWARD EACH OTHER
WHICH WILL START PINCHING THE RIDGE AND EVENTUALLY PUSH IT
SOUTH. DETERMINISTIC MODELS AND THEIR ENSEMBLES ARE IN GREAT
AGREEMENT ON THIS SET UP, AS EVIDENCED BY WPC'S 500 MB CLUSTERS
BEING ALMOST MIRROR IMAGES, SO HAVE A HIGH CONFIDENCE IN THIS
PATTERN. AS THE UPPER LOW OVER NORTHERN CALIFORNIA SLIDES SOUTH,
RIDGING WILL BE ABLE TO MOVE INLAND A BIT FOR TUESDAY AND
WEDNESDAY. THIS WILL ALLOW FOR A WARMING TREND OF TEMPERATURES,
BUT WILL STAY BELOW AVERAGE FOR THIS TIME OF YEAR. NBM KEEPS IN
A 15 TO 30 PERCENT CHANCE OF SHOWERS FOR THIS TIME FRAME,
BELIEVE THIS IS OVERDONE A BIT, SO LOWERED THEM TO 10 TO 20
PERCENT.
ON WEDNESDAY, AN ALL MODELS SHOW AN UPPER TROUGH DROPPING DOWN FROM
THE GULF OF ALASKA. THIS WILL SPREAD THE NEXT BETTER CHANCE FOR
PRECIPITATION INTO THE PACIFIC NORTHWEST. WILL KEEP THE 20 TO 50
PERCENT POPS FROM THE NBM TO SHOW THIS INCREASE. -KRIEDERMAN
AVIATION
06Z TAFS: SHOWER ACTIVITY DIMINISHING IN COVERAGE
ACROSS THE AREA THIS EVENING AS HIGH PRESSURE TEMPORARILY BUILDS
ALOFT BETWEEN SYSTEMS. MAINLY SEEING VFR CONDITIONS WITH SOME
INTERMITTENT BOUTS OF MVFR CEILINGS AS OF 05Z. HREF PROBABILITY
GUIDANCE STILL DEPICTING A 50-70 PERCENT CHANCE FOR MVFR CIGS TO
DEVELOP OVERNIGHT FROM ABOUT KSLE NORTH THROUGH THE PORTLAND
METRO, WITH CIGS TRENDING DOWNWARD BETWEEN 08-12Z. SHOULD SEE
MOSTLY VFR ACROSS THE AREA BY DAYBREAK FRI, WITH INCREASING
OFFSHORE FLOW YIELDING EAST WINDS THROUGH THE GORGE IMPACTING
KTTD AND OTHER PORTLAND AREA TERMINALS AFTER 21Z FRI. A STRONG
FRONT WILL STALL OFFSHORE LATE IN THE PERIOD, POSSIBLY MOVING
CLOSE ENOUGH TO NORTHERN COASTAL AREAS TO BRING RAIN BACK TO KAST
AFTER 00Z SAT.
FOR DETAILED PAC NW AVIATION WEATHER INFORMATION, GO ONLINE TO:
HTTP://WEATHER.GOV/ZSE
KPDX AND APPROACHES...SHOWERS CONTINUE TO DIMINISH OVERNIGHT, WITH
MODEL GUIDANCE DEPICTING AN APPROXIMATELY 70 PERCENT CHANCE FOR
MVFR CIGS FROM FL020-030 AFTER 08Z. CIGS SHOULD IMPROVE BACK TO
VFR BY DAYBREAK FRI. INCREASING OFFSHORE FLOW WILL INDUCE EASTERLY
WINDS OUT OF THE COLUMBIA RIVER GORGE FRI AFTERNOON, POSSIBLY
INCREASING WINDS AT THE TERMINAL TO 10-15 KT AFTER 21Z FRI. /CB
MARINE
BUOY OBSERVATIONS FROM 3 PM PST THURSDAY SHOWED MUCH
WEAKER WINDS AROUND 5 TO 15 KT. SEAS WERE ALSO ON THE DECREASE
WITH SIGNIFICANT WAVE HEIGHTS AROUND 9 TO 11 FT WITH A DOMINANT
WAVE PERIOD AROUND 11 TO 13 SECONDS, LOWEST OVER THE NORTHERN
WATERS. EXPECT SUB-SMALL CRAFT CRITERIA WINDS AND SEAS ACROSS THE
NORTHERN WATERS TONIGHT WHILE THE CENTRAL AND SOUTHERN WATERS
REMAIN RIGHT AROUND 10 FT.
CONDITIONS WILL DETERIORATE QUICKLY ON FRIDAY AS A LARGE LOW
PRESSURE SYSTEM OVER THE FAR NORTHEAST PACIFIC PUSHES A STRONG
FRONTAL OVER THE COASTAL WATERS. IT APPEARS THIS FRONT WILL STALL
OUT, RESULTING IN A FAIRLY PROLONGED PERIOD OF HIGH-END GALE FORCE
SOUTHERLY WIND GUSTS OF 40-45 KT LATE FRIDAY MORNING THROUGH
FRIDAY EVENING. THE CHANCE FOR STORM FORCE WIND GUSTS IN EXCESS OF
48 KT HAS DECREASED EVEN MORE, AND THE NBM V4.0 IS NOW SUGGESTING
THERE IS ONLY A 1% CHANCE AT BUOY 029 AND BUOY 50. MODEL ENSEMBLE
GUIDANCE FROM THE GEFS/EPS BACKS THIS UP WELL. IN OTHER WORDS,
STORM FORCE WIND GUSTS APPEAR HIGHLY UNLIKELY TO OCCUR AT THIS
POINT. IN ADDITION, A SLIGHT OFFSHORE COMPONENT TO WINDS IS
EXPECTED OVER THE INNER WATERS, WHICH IS NOT A FAVORABLE SETUP
FOR A COASTAL JET. THEREFORE, STORM FORCE WIND GUSTS ARE ALSO
HIGHLY UNLIKELY TO OCCUR OVER THE INNER WATERS. WILL MAINTAIN THE
CURRENT GALE WARNING IN EFFECT. NEVERTHELESS, WIND WAVES WILL
LIKELY APPROACH 18-20 FT AND RESULT IN STEEP AND HAZARDOUS SEAS.
WIND GUSTS SHOULD DECREASE A BIT FRIDAY NIGHT AS THE PRESSURE
GRADIENT WEAKENS OVER THE WATERS, BUT SHOULD STILL BE GUSTING TO
35 KT OVER THE OUTER WATERS AND TO 25-30 KT OVER THE INNER WATERS.
LOW-LEVEL OFFSHORE FLOW WILL QUICKLY STRENGTHEN SATURDAY INTO
SUNDAY, RESULTING IN A TRANSITION TO EASTERLY WINDS OVER THE
WATERS. THIS WILL BRING DECREASING SEAS AND MUCH LOWER WIND
SPEEDS, ALTHOUGH WINDS WILL BE LOCALLY ENHANCED DOWNWIND OF GAPS
IN THE COASTAL TERRAIN. -TK
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 9 PM FRIDAY TO 1 PM PST SATURDAY FOR
COLUMBIA RIVER BAR.
SMALL CRAFT ADVISORY FROM 4 AM TO 10 AM PST FRIDAY FOR COASTAL
WATERS FROM CAPE SHOALWATER WA TO CAPE FALCON OR OUT 10 NM.
GALE WARNING FROM 10 AM FRIDAY TO 4 AM PST SATURDAY FOR COASTAL
WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 10 NM.
SMALL CRAFT ADVISORY UNTIL 10 AM PST FRIDAY FOR COASTAL WATERS
FROM CAPE FOULWEATHER OR TO FLORENCE OR OUT 10 NM.
SMALL CRAFT ADVISORY FROM 4 AM TO 8 AM PST FRIDAY FOR WATERS
FROM CAPE SHOALWATER WA TO CAPE FALCON OR FROM 10 TO 60 NM.
GALE WARNING FROM 8 AM FRIDAY TO 10 AM PST SATURDAY FOR COASTAL
WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR FROM 10 TO 60
NM.
SMALL CRAFT ADVISORY UNTIL 8 AM PST FRIDAY FOR COASTAL WATERS
FROM CAPE FOULWEATHER OR TO FLORENCE OR FROM 10 TO 60 NM.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
WWW.TWITTER.COM/NWSPORTLAND
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