224
FXUS66 KPQR 161300
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
500 AM PST MON DEC 16 2024
SYNOPSIS
A SERIES OF FRONTS WILL MAINTAIN ACTIVE WEATHER THROUGH
WEDNESDAY. HEAVIEST PRECIPITATION EXPECTED TONIGHT THROUGH TUESDAY.
SNOW FOR THE CASCADES ABOVE 4000 FT UNTIL SNOW LEVELS RISE ABOVE
7000 FT BY TUESDAY AFTERNOON. BREEZY SOUTHERLY WINDS LATER TUESDAY
INTO EARLY WEDNESDAY. THEN, A COLD FRONT PUSHES ACROSS THE AREA
WEDNESDAY MORNING. DRIER CONDITIONS LIKELY LATER WEDNESDAY THROUGH
FRIDAY, ALTHOUGH WEATHER REMAINS ACTIVE OVER THE PACIFIC AND NEAR
THE COAST. RAIN LIKELY RETURNS FOR THE WEEKEND AS THE UPPER LEVEL
RIDGE SHIFTS EAST ALLOWING FOR FRONTAL SYSTEMS TO PUSH INLAND.
SHORT TERM /THROUGH WEDNESDAY/
AN ACTIVE WEATHER PATTERN WILL
MAINTAIN A SERIES OF FRONTS THROUGH WEDNESDAY, WITH PERIODS OF RAIN,
CASCADE SNOW, AND BREEZY COASTAL WINDS. WATER VAPOR SATELLITE
IMAGERY THIS MORNING SHOWS A LOW PRESSURE SYSTEM SPINNING OVER THE
NE PACIFIC NEAR 45N AND 140W, WHILE THE ASSOCIATED OCCLUDING FRONT
IS LIFTING NORTHWARD ACROSS THE PACIFIC NW. LIGHT RAIN WILL CONTINUE
TO TAPER OFF THROUGH THE MORNING, GIVING WAY TO MOSTLY DRY WEATHER
FOR A PERIOD OF AROUND 8 HOURS. THEN, ANOTHER BAND OF PRECIPITATION
WILL LIFT ACROSS THE AREA LATER THIS AFTERNOON THROUGH THIS EVENING.
THE WEATHER SYSTEM ASSOCIATED WITH THIS FRONT WEAKENS AND MOVES
NORTHEAST AS UPPER LEVEL RIDGING BUILDS OVER THE WEST COAST INTO
BRITISH COLUMBIA. BENEATH THE RIDGE, A WARM FRONT QUICKLY PUSHES
INLAND, BRINGING ENHANCED PRECIPITATION LATER TONIGHT THROUGH
TUESDAY. CONDITIONS ARE EXPECTED TO DRY AGAIN LATER TUESDAY AS THE
FRONT LIFTS FROM SOUTH TO NORTH. A SHORTWAVE TROUGH THEN PUSHES A
COLD FRONT ACROSS THE AREA WEDNESDAY MORNING, BRINGING ANOTHER QUICK
SHOT OF RAIN.
THE MOST IMPACTFUL WEATHER WILL LIKELY BE THE SNOW FOR THE CASCADES
AND CASCADE PASSES. EXPECT LIGHT SNOWFALL TODAY, BUT MODERATE TO
POTENTIALLY HEAVY SNOW AT TIMES TONIGHT. SNOW LEVELS FLUCTUATE
AROUND 4000-5000 FT TODAY WHILE TEMPERATURES AT THE PASSES ARE
GENERALLY EXPECTED TO HOVER AROUND 31-33 DEGREES THROUGH THE DAY,
WITH LITTLE TO NO CHANGE THROUGH TONIGHT. THIS SHOULD LIMIT THE SNOW
TO LIQUID RATIOS (SLR) WHICH IN TURN WILL PRODUCE LOWER SNOW FALL
TOTALS, WITH 'HEAVIER' WET SNOW BEING MORE LIKELY AROUND PASS LEVEL
(4000-5000 FT). IN GENERAL, EXPECT AN ADDITIONAL 10 TO 18 INCHES OF
SNOW ABOVE 4000 FT THROUGH TUESDAY MORNING. THIS IS FAIRLY
CONSISTENT WITH PROBABILISTIC GUIDANCE WHICH SUGGESTS A 30-50%
CHANCE OF EXCEEDING 12 INCHES OF SNOWFALL IN 36 HOURS. ON TUESDAY,
SNOW LEVELS ARE EXPECTED TO QUICKLY RISE OVER 7000 FT AS THE WARM
FRONT LIFTS NORTHWARD. WILL MAINTAIN THE WINTER STORM WARNING FOR
THE HIGH CASCADES THROUGH 10 AM TUESDAY AS TRAVEL WILL LIKELY BE
HAZARDOUS OVER THE PASSES TONIGHT.
THE FRONTAL SYSTEM FOR TUESDAY INTO WEDNESDAY WILL ALSO BRING
POTENTIALLY HEAVY RAIN AND BREEZY SOUTH WINDS TO THE COAST AND
COASTAL MOUNTAINS. THE FRONT WILL BE ASSOCIATED WITH A MODERATE TO
POTENTIALLY STRONG ATMOSPHERIC RIVER THAT GRADUALLY LIFTS NORTHWARD
INTO WESTERN WASHINGTON. THE MAJORITY OF THE MODEL SOLUTIONS HAVE
THIS PLUME OF MOISTURE DIRECTED TOWARD THE OLYMPIC PENINSULA, BUT
STILL EXPECT DECENT RAINFALL ACROSS THE NORTHWEST OREGON COAST INTO
THE WILLAPA HILLS AS PWAT VALUES PEAK AROUND 1.2". 48-HOUR RAINFALL
TOTALS WILL LIKELY EXCEED 2 INCHES ALONG THE COAST (60-80% CHANCE)
WHILE THE COASTAL MOUNTAINS ARE LIKELY TO RECEIVE AROUND 3-5 INCHES.
LATEST HEFS GUIDANCE SUGGESTS ONLY A 20% CHANCE OF COASTAL RIVERS
REACHING MINOR FLOOD STAGE. SOUTHERLY WINDS ARE ALSO EXPECTED TO
INCREASE ALONG THE COAST BY TUESDAY AFTERNOON WITH GUSTS INCREASING
TO AROUND 40-50 MPH, LIKELY PERSISTING THROUGH TUESDAY NIGHT.
CURRENTLY, AROUND A 20-30% CHANCE OF WIND GUSTS EXCEEDING 60 MPH.
BREEZY WINDS ALSO POSSIBLE INLAND TUESDAY NIGHT WITH GUSTS UP TO 30-
40 MPH.
LONG TERM /THURSDAY THROUGH SUNDAY/
WHILE THERE STILL REMAINS
SOME UNCERTAINTY FOR LATER THIS WEEK, THERE IS GOOD AGREEMENT AMONG
THE MODELS AND THEIR ENSEMBLES IN THE OVERALL SYNOPTIC PATTERN.
CLUSTER ANALYSIS OF 500 MB HEIGHTS HAVE BEEN CONSISTENT IN SHOWING
AN AMPLIFIED PATTERN WITH UPPER LEVEL RIDGING OVER MUCH OF THE
WESTERN US FOR THURSDAY AND FRIDAY. WITH UPPER LEVEL TROUGHING OVER
THE PACIFIC, THE WEATHER WILL REMAIN ACTIVE OFFSHORE. FRONTAL
SYSTEMS MAY BRUSH BY NORTHWEST OREGON AND SOUTHWEST WASHINGTON AT
TIMES, BUT AT MOST LIGHT RAIN AT THE COAST, WITH INLAND LOCATIONS
TRENDING MOSTLY DRY WITH OFFSHORE LOW LEVEL FLOW. GENERALLY LESS
THAN A 30% CHANCE OF MEASURABLE RAIN EAST OF THE COAST RANGE UNTIL
SATURDAY. CLUSTERS ARE ALSO IN GOOD AGREEMENT THAT THE UPPER LEVEL
RIDGE SHIFTS EAST BY THE WEEKEND, ALLOWING FOR FRONTAL SYSTEMS TO
PUSH BACK INLAND. SNOW LEVELS APPEAR TO STAY RELATIVELY ELEVATED
ABOVE 5000-6000 FT THROUGH SUNDAY. /DH
AVIATION
CURRENTLY, A WARM FRONTAL BOUNDARY OVER THE INTERIOR
VALLEY CONTINUES TO BRING STRATIFORM PRECIPITATION ACROSS THE
REGION. MOST TERMINALS WILL SEE MVFR CONDITIONS (10-20% CHANCE OF
SHORT-LIVED IFR) THIS MORNING, EXPECTED TO IMPROVE BACK TO VFR BY
19-21Z MONDAY. HOWEVER, THESE IMPROVED CONDITIONS ARE NOT
EXPECTED TO STAY, AS ANOTHER APPROACHING FRONT WILL ARRIVE AROUND
THE AFOREMENTIONED TIME, BRINGING RAIN AND LOWERING CONDITIONS TO
LOW-END MVFR BY 00-02Z TUESDAY. WINDS WILL REMAIN AROUND 7-9 KT
AND SOUTH TO SOUTHEASTERLY THROUGH MOST OF THE PERIOD, THEN
INCREASING TO 10-15 KT WITH GUSTS UP TO 25 KT AT SOME TERMINALS
AROUND 01Z TUESDAY.
AS FOR THE COAST, CURRENT MVFR CONDITIONS WILL IMPROVE TO VFR BY
16-18Z MONDAY, THEN DECREASE TO LOW-END MVFR AROUND 22-23Z MONDAY
AS THE FRONT ARRIVES AT THE COAST. EXPECT SOUTHEASTERLY WINDS
BETWEEN 9-12 KT WITH GUSTS UP TO 15-20 KT THROUGH MOST OF THE TAF
PERIOD (HIGHEST AT KONP). ONCE THE FRONT ARRIVES AT THE COAST,
WINDS WILL PRIMARILY INCREASE FOR KONP, INCREASING SUSTAINED WINDS
TO 15-20 KT WITH GUSTS UP TO 25-30 KT.
PDX AND APPROACHES...CURRENTLY VFR AS OF 12Z MONDAY WITH CIGS
EXPECTED TO LOWER TO MVFR BY 13-15Z MONDAY. CHANCES TO LOWER TO
MVFR ARE AROUND 40-50%, SO CONFIDENCE IS MODERATE THAT CIGS WILL
DETERIORATE TO SUCH FLIGHT CONDITIONS. ONCE THE RAIN BECOMES POST-
FRONTAL RAIN AROUND 19-21Z MONDAY, EXPECT CONDITIONS TO IMPROVE
BACK TO VFR. NEXT FRONTAL SYSTEM PUSHES INLAND BY 01-03Z TUESDAY,
DETERIORATING CIGS AND VIS TO MVFR THROUGH THE REST OF THE TAF
PERIOD. ~HALL
MARINE
LOW PRESSURE WELL OFFSHORE CONTINUES TO PUSH A WARM
FRONT ACROSS THE COASTAL WATERS, WITH GALES EXPECTED ACROSS THE
OUTER COASTAL WATERS EARLY THIS MORNING, GUSTING UP TO 45 KT BEYOND
20 NM. AS OF 4AM, BUOY 46050 AND BUOY 46029 HAVE GUSTED UP TO 42
KT WITHIN THE PAST 2 HOURS. THIS WILL BE SHORT-LIVED, THEREFORE
WILL END THE GALE FORCE WARNING AT 6AM MONDAY. HAVE ISSUED A SMALL
CRAFT ADVISORY TO FOLLOW, WHICH WILL LAST UNTIL TONIGHT. WINDS
REMAIN SOUTHERLY TODAY AS ANOTHER FRONT MOVES ACROSS THE WATERS
TONIGHT. WITH SEAS EXPECTED TO MEET HAZARDOUS SEAS CRITERIA
TONIGHT, HAVE ISSUED A HAZARDOUS SEAS WARNING FROM 10PM MONDAY TO
10AM TUESDAY FOR THE OUTER WATERS AND 1AM TO 10AM TUESDAY FOR THE
INNER WATERS. TUESDAY MORNING, A STRONGER FRONT APPROACHES,
BRINGING A LIKELY CHANCE (70%) FOR GALES BY TUESDAY AFTERNOON.
SEAS NEAR 11 TO 13 FT EARLY THIS MORNING BEGIN TO SUBSIDE. TUESDAY
MORNING, A FRESH SOUTHWESTERLY SWELL WILL BUILD SEAS INTO THE
UPPER TEENS, EXPECTED TO PERSIST UNTIL WEDNESDAY MORNING. ACTIVE
PATTERN CONTINUES BUT AFTER MID-WEEK, VARIOUS MODEL GUIDANCE ARE
NOT IN GREAT AGREEMENT IN TIMING/STRENGTH OF SYSTEMS AFFECTING THE
WATERS. ~HALL/MH
PQR WATCHES/WARNINGS/ADVISORIES
OR...WINTER STORM WARNING UNTIL 10 AM PST TUESDAY FOR ORZ126>128.
WA...WINTER WEATHER ADVISORY UNTIL 10 AM PST TUESDAY FOR WAZ211.
PZ...SMALL CRAFT ADVISORY UNTIL 1 AM PST TUESDAY FOR PZZ210-251>253.
HAZARDOUS SEAS WARNING FROM 1 AM TO 10 AM PST TUESDAY FOR PZZ210-
251>253.
GALE WARNING UNTIL 6 AM PST EARLY THIS MORNING FOR PZZ271>273.
SMALL CRAFT ADVISORY UNTIL 10 PM PST THIS EVENING FOR PZZ271>273.
HAZARDOUS SEAS WARNING FROM 10 PM THIS EVENING TO 10 AM PST
TUESDAY FOR PZZ271>273.
WWW.WEATHER.GOV/PORTLAND
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