181
FXUS66 KPQR 051102
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
359 AM PDT FRI SEP 5 2025
SYNOPSIS
ISOLATED SHOWERS AND THUNDERSTORMS WILL LIFT NORTHWARD
OVER NORTHWEST OREGON EARLY THIS MORNING, REACHING SOUTHWEST WA BY
LATE MORNING. THEN, ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS WILL
MOVE NORTHWARD OVER THE AREA LATE FRIDAY AFTERNOON AND EVENING,
FOLLOWED BY A THIRD ROUND SATURDAY AFTERNOON THROUGH SATURDAY NIGHT.
NOTE SOME LOCATIONS WILL BE MISSED BY ALL THREE ROUNDS GIVEN THE
SHOWERY NATURE OF PRECIPITATION. THE WEATHER PATTERN BECOMES COOLER
EARLY NEXT WEEK WITH SHOWERS BECOMING MUCH MORE WIDESPREAD AS A
CLOSED UPPER LEVEL LOW SETTLES DIRECTLY OVERHEAD. THESE SHOWERS WILL
RESULT IN MORE SUBSTANTIAL RAIN AMOUNTS, WITH ALL LOCATIONS IN
NORTHWEST OREGON AND SOUTHWEST WASHINGTON LIKELY TO SEE AT LEAST SOME
MEASURABLE RAIN (80-90% CHANCE), IF NOT OVER 0.25" (50-70% CHANCE).
SHORT TERM...FRIDAY THROUGH SUNDAY NIGHT
THE SHORT TERM FORECAST
IS HIGHLIGHTED BY A MIX OF CLOUDS AND SUN WITH TEMPERATURES TRENDING
SLIGHTLY COOLER EACH DAY. IN ADDITION, THERE ARE SEVERAL CHANCES FOR
SHOWERS AND THUNDERSTORMS AS 500 MB FLOW REMAINS SOUTHERLY TO
SOUTHEASTERLY AND A SERIES OF DISTURBANCES LIFT NORTHWARD OVER
WESTERN WA/OR. NOTE IT WILL BE DRY MOST OF THE TIME AT ANY GIVEN
LOCATION, AND SOME LOCATIONS WILL BE MISSED COMPLETELY DUE TO THE
SHOWERY NATURE OF PRECIPITATION.
THE FIRST CHANCE FOR SHOWERS AND THUNDERSTORMS IS THROUGH THIS
MORNING AS A SUBTLE UPPER LEVEL SHORTWAVE AND ASSOCIATED VORTICITY
MAX LIFTS NORTHWARD OVER NORTHWEST OREGON, REACHING SOUTHWEST
WASHINGTON BY LATE MORNING. THIS WAVE IS ACCOMPANIED WITH
SUBSTANTIAL ELEVATED INSTABILITY/MOISTURE, AND ISOLATED SHOWERS AND
THUNDERSTORMS WERE ALREADY BEING OBSERVED OVER THE CENTRAL OREGON
COAST RANGE AND AREAS WEST OF EUGENE-SPRINGFIELD BETWEEN 2-3 AM
FRIDAY PER SATELLITE AND RADAR OBSERVATIONS. THESE STORMS ARE
GENERALLY PRODUCING AROUND 0.1" OF RAIN OR LESS WITH VERY LITTLE
WIND. AS SUCH, THE MAIN HAZARD WITH THESE STORMS WILL BE
CLOUD-TO-GROUND LIGHTNING AND POTENTIAL NEW WILDFIRE STARTS. NBM POPS
AND THUNDER PROBABILITIES WERE ADJUSTED UPWARD TODAY TO ACCOUNT FOR
THESE SHOWERS AND STORMS, WHICH ARE NOT BEING HANDLED WELL BY MOST
MODEL GUIDANCE. IT APPEARS THERE WILL THEN BE A BREAK IN
PRECIPITATION MOST OF FRIDAY AFTERNOON, BEFORE A SECOND ROUND OF
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS ARRIVES AFTER 3-5 PM
AND LINGERS THROUGH FRIDAY NIGHT, IMPACTING THE CASCADES BEFORE
SUNSET AND LOCATIONS WEST OF THE CASCADES AROUND OR AFTER SUNSET.
SIMILAR TO THE FIRST ROUND, THE MAIN HAZARD WITH THESE STORMS WILL BE
CLOUD-TO-GROUND LIGHTNING.
THE LATEST SUITE OF HI-RES MODEL GUIDANCE THEN SUGGESTS ANOTHER BREAK
IN PRECIPITATION SATURDAY MORNING/AFTERNOON, FOLLOWED BY A THIRD
ROUND OF SHOWERS AND THUNDERSTORMS THAT ARE SET TO MOVE NORTHWARD
OVER PORTIONS OF NORTHWEST OREGON AND SOUTHWEST WASHINGTON LATE
SATURDAY AFTERNOON AND EVENING. THE CASCADES HAVE THE HIGHEST CHANCE
OF SEEING SHOWERS AND STORMS WITH THE THIRD ROUND, WITH NBM POPS
AROUND 50-70%. PROBABILITIES WEST OF THE CASCADES ARE LOWER, RANGING
FROM 30-45%. THE 00Z ITERATION OF THE ENS SHOWS ENSEMBLE MEAN MUCAPE
VALUES PEAKING WITH THIS THIRD ROUND OF SHOWERS AND STORMS, REACHING
1500-1900 J/KG OVER THE CASCADES AND NEAR 800-1000 J/KG WEST OF THE
CASCADES. WITH 0-6 KM BULK SHEAR VALUES NEAR 20-25 KT IN THE
CASCADES, THE ENVIRONMENT WILL BE SUPPORTIVE OF A FEW STRONGER
THUNDERSTORMS CAPABLE OF PRODUCING HAIL IF ENOUGH FORCING IS IN
PLACE. NOTE HI-RES MODEL GUIDANCE SUGGEST MOST OF SATURDAY'S
THUNDERSTORM ACTIVITY WILL OCCUR NEAR THE CREST AND EAST OF THE
CREST. MODEL SOUNDINGS SUGGEST THESE STORMS WILL BE ELEVATED DUE TO A
STRONG CAPPING INVERSION BETWEEN 750-800 MB PREVENTING SURFACE-BASED
CONVECTION. WITH SOUTHEASTERLY CLOUD-LAYER WINDS, A FEW SHOWERS AND
STORMS MAY DRIFT NORTHWESTWARD INTO THE WILLAMETTE VALLEY. CHANCES
FOR SHOWERS REMAIN IN THE FORECAST ON SUNDAY, MAINLY IN THE
MOUNTAINS. THE LOWLANDS WILL MOST LIKELY BE DRY AT THAT POINT. -TK
LONG TERM...MONDAY THROUGH THURSDAY NIGHT
THE LONG TERM FORECAST
IS HIGHLIGHTED BY A COOL AND SHOWERY WEATHER PATTERN WITH THE
POTENTIAL FOR SUBSTANTIAL RAIN AMOUNTS OVER ALL OF NORTHWEST OR AND
SOUTHWEST WA. THIS WEATHER PATTERN SHIFT IS IN RESPONSE TO A CLOSED
UPPER LEVEL LOW THAT WILL BE SETTLING OVER THE REGION EARLY NEXT
WEEK. THIS LOW IS CURRENTLY CENTERED OVER THE GULF OF ALASKA AND IS
SET TO MOVE TOWARDS THE OREGON/WASHINGTON COAST MONDAY, WITH SHOWERS
LIKELY BECOMING WIDESPREAD OVER THE AREA BY MONDAY AFTERNOON. WITH A
SATURATED THERMODYNAMIC PROFILE/PWAT VALUES OVER 1", SOME SHOWERS
WILL HAVE THE POTENTIAL TO PRODUCE HEAVY RAIN. ALL LOCATIONS FROM THE
COAST TO THE CASCADES WILL LIKELY SEE AT LEAST SOME MEASURABLE RAIN
MONDAY/MONDAY NIGHT (80-90% CHANCE). THERE IS A 50-80% CHANCE FOR
0.25-0.50" OR MORE, WITH THE HIGHEST PROBABILITIES OVER THE CASCADES
AND LANE COUNTY AND THE LOWEST PROBABILITIES OVER SOUTHWEST WA. RAIN
AMOUNTS OF THIS MAGNITUDE WOULD HELP TEMPORARILY DAMPEN FIRE SEASON,
AND CONDITIONS WILL BEGIN TO FEEL MORE FALL-LIKE. -TK
AVIATION
CURRENTLY THE REGION IS CONTENDING WITH TWO DISTINCT
WEATHER FEATURES STRATIFIED WITH HEIGHT WHICH ARE EXPECTED
PROVIDE POTENTIAL IMPACTS MOVING THROUGH THE TAF PERIOD: MARINE
STRATUS AT THE SURFACE AND ISOLATED TO SCATTERED HIGH BASED
THUNDERSTORMS ALOFT. STARTING AT THE SURFACE, NORTHWESTERLY FLOW
AND A ROBUST MARINE LAYER HAS LEAD TO LIFR CONDITIONS ACROSS THE
COAST INTO SOME THE ATTENDANT VALLEYS IN THE COAST RANGE.
CONFIDENCE IS MODERATE TO HIGH FLIGHT CONDITIONS WILL HOLD SUB-
VFR ALONG THE COAST THROUGH THE TAF PERIOD DUE TO PERSISTENT
ONSHORE FLOW WITH A JUMP TO IFR OR LOW-END MVFR BETWEEN 20Z FRI
TO 01Z SAT. HIGHER PROBABILITIES FOR PERSISTENT LIFR/IFR CIGS AND
VIS AT KONP THROUGH THE PERIOD. THERE ARE ALSO INCREASING CHANCES
(50-65%) THIS MORNING FOR MARINE STRATUS TO SURGE INTO THE
PORTLAND METRO AREA, (MAINLY KTTD AND KPDX) IN ADDITION TO KEUG,
BETWEEN 13-18Z LEADING TO MVFR CIGS. AFTER THIS POINT CONDITIONS
LIKELY RETURN TO VFR THE REMAINDER OF THE TAF PERIOD.
A SLIGHT CHANCE FOR THUNDERSTORMS WILL ALSO BE PRESENT AT ALL
SITES TODAY INTO TONIGHT WITH ONGOING HIGH BASED CONVECTION OVER LANE
COUNTY ALREADY IN PROGRESS AS OF 10-11Z. EXPECT THE CURRENT SURGE
OF ACTIVITY TO PROGRESS NORTHWARD-NORTHWESTWARD OVER THE NEXT
SEVERAL HOURS, PRIMARILY IMPACTING KEUG AND KONP, BEFORE
DECREASING FOLLOWED BY ANOTHER POTENTIAL ROUND OF ISOLATED TO
SCATTERED CONVECTION LATER AFTERNOON AND EVENING ~20-22Z ONWARD.
WHILE MODELS INDICATE THIS SECOND ROUND HAS THE POTENTIAL TO PUSH
OFF THE CASCADES INTO THE WILLAMETTE VALLEY AND SW WASHINGTON,
CONFIDENCE IN PLACEMENT/TIMING REMAINS TOO LOW TO INCLUDE THIS
LATTER ROUND IN THE TAF PACKAGE - A FEATURE CERTAINLY WORTH
KEEPING AN EYE ON.
PDX AND APPROACHES...NORTHWESTERLY FLOW AT THE SURFACE CONTINUES
WITH INCREASING CHANCES FOR MVFR CIGS BETWEEN 13-18Z DUE TO A
STRONGER PUSH OF MARINE AIR THAN PAST DAYS. MUCH HIGHER
CONFIDENCE IN PREVAILING VFR AFTER THIS POINT ONWARD. THERE IS
ALSO A 15-20% CHANCE FOR AN ISOLATED SHOWER OR THUNDERSTORM TO
IMPACT THE TERMINAL AFTER 20-21Z FRIDAY THROUGH THE EVENING AND
OVERNIGHT HOURS. -SCHULDT
MARINE
AN AREA OF SURFACE HIGH PRESSURE JUST OFFSHORE CONTINUES
TO DEGRADE TODAY LEADING TO LIGHTER NORTH WINDS COMPARED TO PAST
DAYS - GUSTS UP TO ~15 KNOTS THIS AFTERNOON. THAT SAID, DENSE
COASTAL FOG ALREADY IN PLACE LIKELY PERSISTS THROUGH A DECENT
CHUNK OF THE MORNING HOURS. HEADED THROUGH THE WEEKEND, AN AREA
OF LOW PRESSURE IS EXPECTED TO DROP SOUTHWARD INTO THE AREA
HELPING TO FACILITATE A SWITCH TO SOUTHERLY WINDS ON SATURDAY.
THESE SOUTHERLY WINDS PERSIST THROUGH MONDAY AND TUESDAY BEFORE
TURNING NORTHERLY AGAIN ON WEDNESDAY. SEAS WILL GENERALLY HOLD IN
THE 3-5 FT RANGE INTO EARLY NEXT WEEK. THERE IS A 25-30% CHANCE
OF COMBINED SEAS CLIMBING ABOVE 5 FT DURING THE MIDDLE NEXT WEEK
WITH THOSE PROBABILITIES CLIMBING TO ~50% BY THE END OF NEXT WEEK.
-SCHULDT
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...DENSE FOG ADVISORY UNTIL 7 AM PDT THIS MORNING FOR PZZ210-
251>253.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page