061
FXUS66 KPQR 200547
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
946 PM PST WED FEB 19 2025
SYNOPSIS
FRONTAL SYSTEM CONTINUES TO SHIFT EAST WITH POST
FRONTAL SHOWERS OVER THE NEXT 24 HOURS. CASCADE SNOW WILL
DISSIPATE AS SNOW LEVELS RISE AND PRECIPITATION LESSENS. RAIN
CHANCES REMAIN ALONG THE COAST AND INLAND. A SERIES OF WEATHER
SYSTEMS MOVE IN THROUGH THE WEEKEND WITH HEAVY RAINFALL.
SHORT TERM...NOW THROUGH FRIDAY
SATELLITE SHOWS THE FRONTAL
BAND FROM THE RAINY SYSTEM SHIFTING EASTWARD THIS AFTERNOON,
WITH SHOWERY CONDITIONS OFFSHORE. SHOWERS WILL PERSIST THROUGH
THE DAY WITH SNOW FALLING ALONG THE CASCADES. AN ADDITIONAL 1-3
INCHES OF SNOW IS EXPECTED, THOUGH IT WILL NOT OCCUR DURING THE
DAY AS TEMPERATURES ARE WELL ABOVE FREEZING. SNOW RATIOS ARE
GOING TO BE QUITE LOW THOUGH AS SNOW LEVELS RISE. THIS MEANS
THAT SNOW THAT DOES FALL WILL BE ON THE WETTER SIDE AND THUS
TRUE ACCUMULATION MAY BE DIFFICULT. SNOW AT THE PASS LEVEL IS
EXPECTED.
TRANSITIONING INTO THURSDAY AND FRIDAY, CONDITIONS BECOME MUCH
MORE SETTLED WITH A TRANSIENT RIDGE MOVING OVERHEAD. SOME
LINGERING SHOWERS EARLY THURSDAY. EASTERLY WINDS WILL RETURN
WHICH WILL USHER IN DRIER AIR, CLEARER SKIES, AND COLDER
TEMPERATURES. OVERNIGHT THURSDAY INTO FRIDAY MORNING,
TEMPERATURES WILL BE THE LOWEST OF THE WEEK DUE TO A COMBINATION
OF EASTERLY WINDS AND RADIATIONAL COOLING FROM CLEARER
SKIES. COULD SEE SOME AREAS OF PATCHY FOG, IN AREAS THAT REMAIN
ABOVE FREEZING, AND NEAR THE COAST RANGE AND THE SOUTHERN
WILLAMETTE VALLEY WHERE WIND SPEEDS WILL BE LOWER.-MUESSLE
LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY
SATURDAY IS WHEN
THE WEATHER BEGINS TO TURN AS A SERIES OF FRONTAL SYSTEMS MAKE
THEIR WAY TOWARDS THE PACIFIC NORTHWEST. GLOBAL MODELS ARE IN
FAIRLY GOOD AGREEMENT WITH THE OVERALL SYNOPTIC PATTERN, BUT
DISAGREE IN REGARDS TO THE EXACT TRACK AND IMPACTS OF THE RAIN.
THE FIRST SYSTEM ARRIVES FRIDAY NIGHT AS A NORTHEAST PACIFIC
LOW ADVECTS DOWN THE COASTLINE FROM THE GULF OF ALASKA TO
VANCOUVER ISLAND. THIS COLD AIR WRAPPED LOW WILL NOT NECESSARILY
BE AS IMPACTFUL TO OUR AREA, BUT WILL BRING WITH IT
PRECIPITATION AND WILL AID IN BREAKING DOWN THE RIDGE. MOST RAIN
WILL FALL TO OUR NORTH.
THE NEXT SYSTEM IS MUCH MORE ROBUST AS A TRAILING WARM FRONT ADVECTS
IN. THIS FRONT WILL BE MUCH WETTER AND POTENTIALLY MORE
IMPACTFUL IN THE LONG RUN. THIS FRONT WILL START MOVING INLAND
ON SATURDAY AFTERNOON, THEN INTENSIFY AS THE BULK OF THE
MOISTURE SHIFTS SOUTHWARD NEARLY DIRECTLY OVER THE FORECAST AREA.
LOOKING AT THE GLOBAL CLUSTER ANALYSIS THERE IS GOOD AGREEMENT WE
WILL BE IMPACTED BY THIS STORM SYSTEM, BUT SUBTLE DIFFERENCES IN THE
SYNOPTIC PATTERN BETWEEN ENSEMBLE MEMBERS RESULT IN PORTIONS OF THE
AREA RECEIVING MORE RAIN WHILE OTHERS RECEIVE LESS RAIN SO
CONFIDENCE IS RELATIVELY LOW IN EXACTLY WHERE THE AXIS OF HIGHEST
RAINFALL TOTALS WILL OCCUR ACROSS THE CWA. THE EPS, GEFS AND GEPS
HAVE ALL TRENDED WETTER OVER THE PAST 24 HOURS. IN TILLAMOOK, THE 24-
HR RAINFALL TOTALS ENDING AT 7AM SUNDAY RANGE FROM A >95% CHANCE OF
0.5 INCH, TO A 10% CHANCE OF GREATER THAN 3.5 INCHES. SOUTHWESTERLY
FLOW WILL PROMOTE SOME "RAIN SHADOWING" FOR THE WILLAMETTE VALLEY SO
RAINFALL AMOUNTS SHOULD END UP LESS THAN THE ADJACENT HIGHER TERRAIN
IN THE COAST RANGE AND CASCADES.
ON SUNDAY, THERE IS A SECOND SURGE OF PRECIPITATION THAT IS MORE
LIKELY TO CAUSE IMPACTS GIVEN THE WIDESPREAD RAIN OVER THE PRECEDING
12-18 HOURS AND THE ONGOING SNOWMELT ACROSS THE FOOTHILLS. THE
COMBINATION OF THE TWO STORM SYSTEMS WILL MAKE FOR A VERY WET
WEEKEND. IN THE 48 HOURS COVERING BOTH SATURDAY AND SUNDAY, RAINFALL
TOTALS WILL RANGE IN THE "INCHES". FOR EXAMPLE, WITHIN THE COAST
RANGE, THERE IS AROUND AN 80% CHANCE OF 3 INCHES OR MORE OF RAIN,
AND NEARLY A 25% CHANCE OF 5 INCHES OR MORE. THE WILLAMETTE VALLEY
IN CONTRAST HAS LESS THAN A 5% CHANCE OF 3 INCHES OF RAIN. WITH THIS
AMOUNT OF PRECIPITATION, HEFS GUIDANCE SUGGESTS A 10-15% CHANCE FOR
OUR FASTER RESPONDING RIVERS IN THE COAST RANGE, SUCH AS THE WILSON
RIVER FOR EXAMPLE, TO REACH MINOR FLOOD STAGE LATE IN THE WEEKEND.
SNOW LEVELS WILL RISE UP TO 6500-7000 FT SO DON'T EXPECT A DUMPING
OF SNOW THIS WEEKEND.
AVIATION
HIGH PRESSURE BUILDING INTO THE REGION WILL PRODUCE
MAINLY VFR CONDITIONS THROUGH 06Z FRIDAY AND A MIXTURE OF MVFR AND
VFR CONDITIONS ALONG THE COAST. HOWEVER, LOW LEVEL WESTERLY FLOW
AND A LOWERING INVERSION IS INCREASINGLY PRODUCING A RAIN SHADOW
ALONG THE INTERSTATE 5 CORRIDOR AND ALLOWING SOME BREAKS IN THE
CLOUD COVER TO MATERIALIZE. DECREASING WINDS, PLENTY OF LOW LEVEL
MOISTURE AND A DEVELOPING SURFACE INVERSION SHOULD PROMOTE SOME
DIPS INTO MVFR TO LIFR THRESHOLDS AT MOST INLAND TAF SITES. HIGH
RESOLUTION MODEL GUIDANCE SUGGESTS KHIO AND KPDX HAVE THE HIGHEST
PROBABILITY FOR FOG DEVELOPING AT NEAR 50-60%, BUT EVEN THIS HIGH
RESOLUTION MODEL GUIDANCE SUGGESTS A 20-30% CHANCE FOR SITES LIKE
KSLE AND KEUG. FOG COVERAGE APPEARS MOST LIKELY TO INCREASE
ABRUPTLY BETWEEN 12-15Z THURSDAY ASSUMING A CLOUD DECK DOES NOT
SOLIDIFY OVER INLAND NORTHWEST OREGON BETWEEN NOW AND THEN. GIVEN
THE SHALLOW NATURE OF THE SURFACE INVERSION ANTICIPATED, ANY MIST
OR FOG THAT DOES DEVELOP SHOULD DISSIPATE RATHER QUICKLY BETWEEN
17-20Z THURSDAY.
PDX AND APPROACHES...HIGH PRESSURE BUILDING INTO THE REGION WILL
PRODUCE MAINLY VFR CONDITIONS THROUGH 06Z FRIDAY. HOWEVER, LOW LEVEL
WESTERLY FLOW AND A LOWERING INVERSION ALOFT IS INCREASINGLY
PRODUCING A RAIN SHADOW ALONG THE INTERSTATE 5 CORRIDOR AND
ALLOWING SOME BREAKS IN THE CLOUD COVER TO MATERIALIZE. LIGHT
WINDS, PLENTY OF LOW LEVEL MOISTURE AND A DEVELOPING SURFACE
INVERSION SHOULD PROMOTE SOME DIPS INTO MVFR TO LIFR THRESHOLDS.
GIVEN THE SHALLOW NATURE OF THE SURFACE INVERSION ANTICIPATED,
ANY FOG THAT DOES DEVELOP SHOULD DISSIPATE BETWEEN 17-20Z THURSDAY.
MARINE
A FRONTAL SYSTEM TRACKING INLAND FROM THE NORTHEAST
PACIFIC WILL CONTINUE TO YIELD DIMINISHING WESTERLY WINDS THROUGH
TONIGHT. GALE WARNINGS HAVE THEREFORE BEEN CANCELLED AND REPLACED
WITH SMALL CRAFT ADVISORIES FOR BOTH INNER AND OUTER WATERS
THROUGH 4 AM THURSDAY. SEAS OF 12-14 FT WILL SUBSIDE TO 8-10 FT
BY THURSDAY MORNING, CONTINUING THROUGH THURSDAY NIGHT.
ANOTHER FRONTAL SYSTEM WILL APPROACH THE WATERS FRIDAY INTO
SATURDAY, ALTHOUGH SOME UNCERTAINTY REMAINS IN THE POTENTIAL TRACK
AND INTENSITY OF THIS LOW. CONFIDENCE IN THE OCCURRENCE OF
SOUTHERLY GALE-FORCE WINDS SATURDAY OR SATURDAY NIGHT IS
INCREASING, CURRENTLY ASSESSED AS A 70-90 PERCENT LIKELIHOOD.
THERE IS CONTINUED MODERATE CONFIDENCE IN MAXIMUM GUSTS EXCEEDING
STORM-FORCE, ASSESSED AT 50-60% LIKELIHOOD AT THIS LEAD TIME. SEAS
LOOK TO SIMILARLY BUILD TO 12-14 FT, WHILE THERE IS A 25% CHANCE
SIGNIFICANT WAVE HEIGHTS EXCEED 15 FT. SEAS OF 9-12 FT THEN LOOK
TO CONTINUE THROUGH AT LEAST MONDAY. -PICARD
PQR WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY UNTIL 4 AM PST THURSDAY FOR ORZ126>128.
WA...WINTER WEATHER ADVISORY UNTIL 4 AM PST THURSDAY FOR WAZ211.
PZ...SMALL CRAFT ADVISORY UNTIL 1 AM PST THURSDAY FOR PZZ210.
SMALL CRAFT ADVISORY UNTIL 4 AM PST THURSDAY FOR PZZ251>253-
271>273.
WWW.WEATHER.GOV/PORTLAND
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