403
FXUS66 KPQR 232236
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
336 PM PDT WED APR 23 2025
SYNOPSIS
HIGH PRESSURE WILL MAINTAIN DRY WEATHER AND MOSTLY
CLEAR SKIES THROUGH THURSDAY AFTERNOON. AN APPROACHING SYSTEM
WILL BRING A 15 TO 20 PERCENT CHANCE OF THUNDERSTORMS THURSDAY
EVENING ACROSS THE LINN AND LANE COUNTY CASCADES AS WELL AS THE
SOUTHERN WILLAMETTE VALLEY. COOLER TEMPERATURES AND MOSTLY DRY
CONDITIONS EXPECTED THIS WEEKEND WITH LINGERING SHOWERS OVER THE
CASCADES.
SHORT TERM...NOW THROUGH FRIDAY NIGHT
HIGH PRESSURE WILL
MAINTAIN DRY WEATHER WITH MOSTLY CLEAR SKIES ACROSS NORTHWEST
OREGON AND SOUTHWEST WASHINGTON THROUGH TOMORROW (THURSDAY)
MORNING. EXPECT THIS AFTERNOON'S HIGHS IN THE UPPER 60S TO LOW
70S FOR INTERIOR VALLEYS, AND UPPER 50S TO LOW 60S ALONG THE
COAST. TOMORROW IS FORECAST TO BE THE WARMEST DAY OF THE WEEK,
WITH HIGHS IN THE MID TO UPPER 70S FOR INTERIOR VALLEYS. CAN'T
RULE OUT REACHING 80 DEGREES IN THE GREATER PORTLAND/VANCOUVER
METRO AREA, WITH NBM SUGGESTING A 40-60% PROBABILITY OF CERTAIN
AREAS EXCEEDING 80 DEGREES. OVERNIGHT LOWS REMAIN SEASONABLY
COOL, GENERALLY IN THE 40S. WINDS WILL BE LIGHT AND OUT OF THE
NORTHWEST TODAY, WITH GUSTS UP TO 20-25 MPH ALONG THE COAST.
TOMORROW, A WEAK THERMAL TROUGH MOVING NORTHWARD WILL RETURN
5-15 MPH EASTERLY WINDS FOR COASTAL AND INLAND AREAS NORTH OF
TILLAMOOK AND SALEM.
THURSDAY EVENING (MAINLY 3-11 PM THURSDAY), AN UPPER-LEVEL
TROUGH WILL APPROACH THE PACIFIC NORTHWEST, TURNING FLOW ALOFT
MORE SOUTHERLY TO SOUTHEASTERLY. THIS PATTERN WILL FAVOR MORE
MOISTURE ADVECTION FROM THE SOUTH, AS WELL AS ELEVATED
INSTABILITY AS COOLER AIR MOVES IN ALOFT. THE LATEST HREF
GUIDANCE SHOWS MUCAPE VALUES BETWEEN 100-400 J/KG ACROSS THE
LINN/LANE COUNTY CASCADES AND SOUTHERN WILLAMETTE VALLEY, WHICH
IS ENOUGH TO PRODUCE SOME ISOLATED THUNDERSTORMS. TAKING A LOOK
AT HREF SOUNDINGS, WIND SPEEDS ALOFT LOOK WEAK (NO STRONGER
THAN 20-30 KT) AND DIRECTIONAL WIND SHEAR LOOKS MINIMAL, SO ANY
THUNDERSTORMS THAT DEVELOP ARE EXPECTED TO BE SUB-SEVERE. THE
SOUNDINGS ARE ALSO SHOWING SOME OF THAT INSTABILITY TAPPING INTO
THE -10 TO -30 DEG C HAIL GROWTH ZONE. THEREFORE, POTENTIAL
IMPACTS FROM ANY ISOLATED THUNDERSTORMS WOULD BE LIGHTNING,
SMALL HAIL (LIKELY BB-SIZED), BRIEF DOWNPOURS, AND BRIEF GUSTY
OUTFLOW WINDS. NBM DOESN'T CAPTURE ELEVATED THUNDERSTORMS VERY
WELL, SO WENT AHEAD AND INCREASED THUNDERSTORM PROBABILITIES TO
15-20% (SLIGHT CHANCE) FOR THE LINN/LANE COUNTY CASCADES AND
SOUTHERN WILLAMETTE VALLEY THURSDAY EVENING. WILL NOTE THAT THE
SOUTH-SOUTHEAST STEERING FLOW ALOFT COULD PUSH SOME CONVECTIVE
DEBRIS INTO THE COAST RANGE OR EVEN THE COAST. THE SLIGHT CHANCE
FOR THUNDERSTORMS WILL DIMINISH LATE THURSDAY NIGHT INTO EARLY
FRIDAY MORNING AS INSTABILITY ALOFT DECREASES.
FRIDAY IS BEGINNING TO TREND DRIER FOR MORE LOCATIONS WEST OF
THE CASCADES. GUIDANCE IS TRACKING THE UPPER LEVEL TROUGH MORE
SOUTHEASTWARD INTO CALIFORNIA. THEREFORE, THE HIGHEST
PROBABILITIES FOR PRECIPITATION REMAIN ACROSS THE CASCADES
(50-80%) AS SHOWERS WRAP AROUND THE LOW. WEST OF THE CASCADES,
PROBABILITY OF PRECIPITATION HAS DECREASED TO AROUND 15-40%.
MANY LOCATIONS MAY SEE AT MOST A SPRINKLE OR REMAIN COMPLETELY
DRY. THE PROBABILITY OF 24 HOUR RAINFALL EXCEEDING 0.25 INCH (5
AM FRIDAY TO 5 AM SATURDAY) HAS FALLEN TO 10-20% WEST OF THE
CASCADES, AND 30-60% IN THE CASCADES (HIGHEST OVER THE LINN/LANE
COUNTY CASCADES). WITH THE LOW TRACKING FURTHER SOUTH, SKIES
ARE TRENDING MORE SCATTERED OR BROKEN THE CLOSER YOU GET TO THE
PORTLAND/VANCOUVER METRO AND SOUTHWEST WASHINGTON. THIS IS
LEADING TO WARMER FORECAST TEMPERATURES ON FRIDAY FOR INTERIOR
VALLEYS, WITH UPPER 60S TO LOW 70S ESPECIALLY NORTH OF SALEM.
-ALVIZ
LONG TERM...SATURDAY THROUGH TUESDAY
AS THE AFOREMENTIONED
UPPER LEVEL TROUGH CONTINUES TO MOVE INTO THE INTERMOUNTAIN
WEST, COOLER AIR WILL SETTLE INTO THE AREA AND PRECIPITATION
CHANCES WILL GRADUALLY DECREASE. DAYTIME HIGHS ARE FORECAST TO
FALL INTO THE 60S ACROSS INTERIOR VALLEYS. MOST AREAS WILL
REMAIN DRY, BUT THE CASCADES MAY CONTINUE TO SEE SOME LINGERING
SHOWERS. HEADING INTO EARLY NEXT WEEK (MONDAY-TUESDAY), THE
MAJORITY OF GFS, EURO, AND CANADIAN ENSEMBLE MEMBERS ARE
SHOWING AN UPPER LEVEL RIDGE SHIFTING INTO THE PACIFIC
NORTHWEST, LEADING TO SLIGHTLY WARMER TEMPERATURES. HOWEVER,
ABOUT 25% OF ENSEMBLE MEMBERS DO SHOW A SHORTWAVE TROUGH COMING
IN BY TUESDAY, SO THERE REMAINS SOME SLIGHT CHANCES FOR
PRECIPITATION EARLY NEXT WEEK. -ALVIZ
AVIATION
AT 2030Z WEDNESDAY, SATELLITE AND SURFACE WEATHER
OBSERVATIONS DEPICTED CLEAR SKIES ACROSS NORTHWEST OR AND
SOUTHWEST WA UNDER HIGH PRESSURE. WINDS WERE OUT OF THE NORTH TO
NORTHWEST, STRONGEST AT KONP WHERE GUSTS UP TO 20-25 KT ARE BEING
OBSERVED. COASTAL WINDS WILL DECREASE AFTER 02-04Z THURSDAY WITH
WINDS TURNING OFFSHORE OVERNIGHT. THIS WILL HELP MAINTAIN CLEAR
SKIES THROUGH 12Z THURSDAY, FOR BOTH THE COAST AND INLAND AREAS.
THE ONE POTENTIAL EXCEPTION IS AT KONP WHERE OFFSHORE WINDS
TONIGHT MAY BE TOO WEAK TO PREVENT THE DEVELOPMENT OF LOW STRATUS.
THIS IS NOT THE MOST LIKELY OUTCOME THOUGH, AS THE PROBABILITY
FOR LOW CLOUDS TO DEVELOP (CIGS BELOW 1000 FT) IS AT ONLY 15-20%.
THEREFORE, HAVE DECIDED TO MAINTAIN VFR CONDITIONS AT KONP
THROUGH THE TAF PERIOD.
PDX AND APPROACHES...VFR CONDITIONS AND CLEAR SKIES CONTINUE
THROUGH THE TAF PERIOD WITH NORTHWEST WINDS AROUND 5-10 KT. -TK
MARINE
STRONG HIGH PRESSURE OFFSHORE WILL MAINTAIN NORTHERLY TO
NORTHWESTERLY WINDS ACROSS THE COASTAL WATERS THROUGH THE
UPCOMING WEEKEND. THE STRONGEST WINDS EXPECTED AT ANY TIME THIS
WEEK ARE OCCURRING RIGHT NOW DUE TO A SURFACE THERMAL TROUGH ALONG
THE SOUTH OREGON COAST TIGHTENING THE SURFACE PRESSURE GRADIENT
OVER THE COASTAL WATERS, RESULTING IN BREEZY NORTH WINDS WITH
GUSTS UP TO 20-30 KT AND SEAS AROUND 5 TO 7 FT. EXPECT THESE
CONDITIONS TO CONTINUE THROUGH WEDNESDAY EVENING. A SMALL CRAFT
ADVISORY REMAINS IN EFFECT FOR ALL MARINE ZONES (EXCEPT THE
COLUMBIA RIVER BAR) UNTIL 11 PM TONIGHT.
THE THERMAL TROUGH WILL BREAK DOWN WEDNESDAY NIGHT, ALLOWING
WINDS TO EASE WEDNESDAY NIGHT INTO THURSDAY. SEAS ARE EXPECTED TO
PERSIST AROUND 5 TO 8 FT AT 10 TO 12 SECONDS THROUGH FRIDAY. -TK
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 11 PM PDT THIS EVENING FOR PZZ251>253-
271>273.
WWW.WEATHER.GOV/PORTLAND
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