735
FXUS66 KPQR 051742
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1042 AM PDT FRI SEP 5 2025
UPDATED AVIATION DISCUSSION.
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 IFR 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 MVFR
BETWEEN 20Z FRI TO 02Z SAT. HOWEVER, THE KAST AREA MAY SEE A FEW
HOURS OF VFR CONDITIONS DURING THIS TIMEFRAME. HIGHER PROBABILITIES
FOR PERSISTENT LIFR/IFR CIGS AND VIS AT KONP THROUGH THE PERIOD. FOR
INLAND AREAS, EXPECTING MAINLY VFR CONDITIONS EXCEPT FOR PERIODS OF
MVFR/IFR CONDITIONS IN SHOWERS. AS THE ONSHORE FLOW INCREASES
TONIGHT, MARINE STRATUS COULD PUSH INLAND AGAIN WITH A 40-70% CHANCE
OF MVFR CEILINGS AT MOST INLAND TERMINALS, EXCEPT FOR 60-80% CHANCE
AT KEUG, BEGINNING BETWEEN 10-14Z SAT. CONDITIONS EXPECTED TO LIFT
TO VFR AFTER 18-20Z SAT.
A SLIGHT CHANCE FOR THUNDERSTORMS WILL ALSO BE PRESENT AT ALL SITES
TODAY INTO TONIGHT. THE CURRENT ROUND OF SHOWERS AND ISOLATED
THUNDERSTORMS WILL BE DECREASING BY 18-19Z. THEN ANOTHER POTENTIAL
ROUND OF ISOLATED TO SCATTERED CONVECTION IS EXPECTED LATER THIS
AFTERNOON AND EVENING FROM ~20-22Z ONWARD. WHILE MODELS INDICATE
THIS SECOND ROUND INDICATES STORMS WILL BEGIN OVER THE CASCADES,
THERE IS THE POTENTIAL FOR THEM TO PUSH INTO THE WILLAMETTE VALLEY
AND SW WASHINGTON AGAIN. HOWEVER, 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 MVFR CONDITIONS THROUGH 19Z DUE TO SHOWERS AND MARINE STRATUS.
MUCH HIGHER CONFIDENCE IN PREVAILING VFR AFTER THIS POINT ONWARD
BEFORE A 40-60% CHANCE OF MVFR CEILINGS RETURNING AFTER 12-14Z SAT,
CLEARING TO VFR BY 18-21Z. THERE IS ALSO A 15-20% CHANCE FOR AN
ISOLATED SHOWER OR THUNDERSTORM TO IMPACT THE TERMINAL AFTER 22Z
FRIDAY THROUGH THE EVENING AND OVERNIGHT HOURS. -SCHULDT/HEC
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...NONE
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