798
FXUS66 KPQR 092253
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
353 PM PDT TUE SEP 9 2025
SYNOPSIS
SHOWERS AND THUNDERSTORMS CONTINUE THIS AFTERNOON
AND EVENING, MAINLY FOCUSED OVER THE SOUTHERN WILLAMETTE VALLEY
AND OREGON CASCADES WHERE ACTIVITY OCCURRED YESTERDAY. AREAS
THAT STAYED DRY ON MONDAY ARE LIKELY TO STAY DRY TODAY. THUNDER
CHANCES PERSIST INTO WEDNESDAY, PRIMARILY ALONG THE CASCADES,
BEFORE CONDITIONS TREND WARMER AND DRIER LATE THIS WEEK.
CONFIDENCE HAS DROPPED FOR WIDESPREAD RAIN LATE IN THE WEEKEND,
THOUGH IT STILL REMAINS A POSSIBILITY.
SHORT TERM...NOW THROUGH THURSDAY NIGHT
AROUND 2 PM,
CONVECTION HAD BEGUN TO BUILD OVER THE SOUTHWEST WASHINGTON
CASCADES AND MOST OF THE NORTHWEST OREGON CASCADES, WHICH IS
CONSISTENT WITH GUIDANCE. THESE STORMS WILL REMAIN THE MAIN
FOCUS FOR THE REMAINDER OF THE AFTERNOON AND EVENING, WITH MUCH
OF THE WASHINGTON AND OREGON COAST EXPECTED TO STAY DRY. WHILE
THUNDERSTORMS MAY DRIFT WESTWARD INTO THE SOUTHERN WILLAMETTE
VALLEY THIS EVENING, EXPECT LESSER CHANCES TO SEE SHOWERS AND
THUNDERSTORMS IN THE VALLEY NORTH OF SALEM, OR. LOCALLY HEAVY
RAINFALL AND REMAINS POSSIBLE IN STRONGER CORES, BUT ACTIVITY
WILL STAY HIT OR MISS, SO PRECIPITATION TOTALS WILL BE QUITE
VARIABLE.
HIGH-RESOLUTION GUIDANCE CONTINUES TO HIGHLIGHT A 20-40% CHANCE
OF HOURLY RAINFALL RATES EXCEEDING 0.75 INCHES, PARTICULARLY
OVER THE LANE COUNTY CASCADES THIS AFTERNOON AND EVENING. SHOULD
THIS MATERIALIZE, THERE WOULD BE AN ELEVATED RISK FOR DEBRIS
FLOWS ON VULNERABLE BURN SCARS, THOUGH OVERALL CONFIDENCE IN
SUCH HIGH-END RAIN RATES REMAINS LOW, ESPECIALLY AROUND THE
EMIGRANT FIRE. FOR THIS REASON, NO WATCHES HAVE BEEN ISSUES, BUT
THE POTENTIAL FOR IMPACTS IS WORTH NOTING.
THUNDERSTORM CHANCES APPEAR WEAKER ON WEDNESDAY AND MORE
CONFINED TO THE OREGON CASCADE CRESTS ITSELF. FORECAST SOUNDINGS
SHOW REDUCED CAPE AND A SOMEWHAT STRONGER INVERSION, WHICH
SHOULD LIMIT BOTH UPDRAFT STRENGTH AND STORM COVERAGE. STILL, A
FEW ISOLATED STORMS CANNOT BE RULED OUT, ESPECIALLY DURING PEAK
HEATING HOURS. BY THURSDAY, SHOWER ACTIVITY BECOMES
INCREASINGLY CONFINED TO THE HIGH CASCADES BEFORE TAPERING OFF
ALTOGETHER THURSDAY NIGHT AS A SHORTWAVE RIDGE APPROACHES THE
COAST.
LONG TERM...FRIDAY THROUGH MONDAY NIGHT
A MORE STABLE PATTERN
ARRIVES FRIDAY AND SATURDAY AS A SHORTWAVE RIDGE BUILDS
OVERHEAD. DRY CONDITIONS AND WARMER AFTERNOONS ARE EXPECTED,
WITH INLAND HIGHS CLIMBING INTO THE UPPER 70S TO NEAR 80, AND
COASTAL HIGHS IN THE 60S.
FORECAST CONFIDENCE DECREASES LATE SATURDAY INTO SUNDAY AS
ENSEMBLE SOLUTIONS DIVERGE ON THE TRACK OF THE NEXT UPPER
TROUGH. SOME KEEP THE SYSTEM INTACT, FAVORING WIDESPREAD RAIN,
WHILE MOST OF THE OTHER MODELS SPLIT IT SOUTH INTO NORTHERN
CALIFORNIA AND LEAVE OUR REGION A BIT DRIER. CURRENT CHANCES FOR
AT LEAST A QUARTER INCH OF RAIN STAND NEAR 40-50% FOR SATURDAY
AND 40-60% FOR SUNDAY FOR MUCH OF NORTHWEST OREGON AND SOUTHWEST
WASHINGTON, HIGHEST ALONG THE OREGON CASCADES. TEMPERATURES
SUNDAY WILL HINGE ON RAINFALL COVERAGE - LOW TO MID 70S IF WET,
UPPER 70S TO LOW 80S IF DRY. UNCERTAINTY LINGERS INTO EARLY
NEXT WEEK WITH LOW-END (20-30%) SHOWER CHANCES CONTINUING
THROUGH MONDAY AND HIGHS RANGING FROM THE 60S AT THE COAST TO
THE 70S INLAND. ~HALL
AVIATION
AN UPPER LEVEL LOW PRESSURE SYSTEM CONTINUES TO DRIFT
EASTWARD OVER THE PACNW AND NORTHERN CALIFORNIA. THIS IS
SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE CASCADES
AND CASCADE FOOTHILLS. PRECIPITATION IS DRIFTING WESTWARD TOWARDS
THE VALLEY BUT CONFIDENCE ANY PRECIPITATION IMPACTS THE INLAND
TERMINALS IS LOW, THOUGH PROB30S AT KSLE AND KEUG REMAIN
WARRANTED. LIGHTNING, ERRATIC WINDS, AND HEAVY RAIN ARE THE MAIN
THREATS WITH THE THUNDERSTORMS. HIGHER PRESSURE ALOFT IS EXPECTED
TO BUILD TONIGHT ALONG WITH MOISTENING CONDITIONS WILL SUPPORT A
MORE ROBUST MARINE LAYER WITH IFR/MVFR CIGS ALONG THE COAST AND
POSSIBLY INLAND. PROBS FOR MVFR OR LOWER CIGS ALONG THE COAST
INCREASE AFTER 00-02Z WED TO 60-80% AND PERSIST THROUGH 18-20Z.
MVFR CLOUD COVER MAY DEVELOP INLAND AS WELL BETWEEN 10-12Z BUT
PROBABILITIES JUMP AROUND A BIT MORE 20-50% THROUGH 18-20Z.
KPDX AND APPROACHES...PREDOMINATELY VFR. INTERMITTENT SHOWERS AND
POSSIBLY A THUNDERSTORM WITH LIGHT WEST-NORTHWESTERLY WINDS UNDER
10 KT WILL CONTINUE THROUGH THE EVENING. ANY HEAVY RAIN MAY LEAD
TO BRIEF MVFR CIGS AND/OR VIS. 40-60% CHANCE FOR MVFR/IFR CIGS TO
DEVELOP 10-12Z WED, MAINLY AROUND KTTD AND KPDX. -BATZ
MARINE
HIGH PRESSURE OVER THE WATERS WILL MAINTAIN NORTHERLY
TO NORTHWESTERLY WINDS WITH GUSTS LESS THAN 15 KT THROUGH FRIDAY.
SEAS REMAIN AROUND 2-4 FT AT 10-12 SEC THROUGH WEDNESDAY, BUILDING
TO 5-7 FT AT 11-12 SEC BY FRIDAY WITH A WEST-NORTHWESTERLY SWELL.
HEADING INTO THE WEEKEND, GUIDANCE IS SUGGESTING ANOTHER LOW
PRESSURE SYSTEM APPROACHING THE PACIFIC NORTHWEST. A FRONT
ASSOCIATED WITH THIS LOW WILL WEAKEN AS IT MOVES ACROSS THE WATERS
SATURDAY AND SUNDAY. THE WINDS WILL SHIFT SOUTHERLY AHEAD OF THE
FRONT ON SATURDAY, THEN NORTHERLY WITH AND BEHIND THE FRONT ON
SUNDAY. PROBABILITIES FOR WIND GUSTS OF 21 KT OR GREATER (SMALL
CRAFT CONDITIONS) ACROSS THE WATERS SATURDAY RANGE FROM 30-50%,
HIGHEST ACROSS THE OUTER WATERS. PROBABILITIES INCREASE SUNDAY TO
50-70% FOR ALL MARINE ZONES. GIVEN THE LEAD TIME WILL HOLD OFF ON
ISSUING ANY PRODUCTS BUT THIS WILL BE SOMETHING TO KEEP IN MIND
FOR THE COMING WEEKEND. SEAS ARE FORECAST AROUND 5-7 FEET AT
10-12 SEC THROUGH THE WEEKEND. -BATZ/ALVIZ
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
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