996
FXUS66 KPQR 061011
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
310 AM PDT SAT SEP 6 2025
SYNOPSIS
THUNDERSTORMS PRODUCING FREQUENT LIGHTNING, SMALL HAIL
AND LOCALLY HEAVY RAIN WILL CONTINUE OVER MUCH OF NORTHWEST OREGON
AND SOUTHWEST WASHINGTON THIS MORNING. ANOTHER ROUND OF SHOWERS AND
STORMS IS EXPECTED LATE THIS AFTERNOON INTO TONIGHT, ALBEIT MORE
FOCUSED OVER THE CASCADES/FOOTHILLS AND EASTERN PORTIONS OF THE
WILLAMETTE VALLEY. TRENDING COOL, WET AND SHOWERY MONDAY THROUGH
TUESDAY AS A CLOSED UPPER LEVEL LOW SETTLES OVER THE AREA.
SHORT TERM...NOW THROUGH SUNDAY NIGHT
SINCE 12 AM SATURDAY,
NUMEROUS THUNDERSTORMS HAVE BEEN OBSERVED OVER THE COAST RANGE,
WILLAMETTE VALLEY AND PORTIONS OF THE CASCADE FOOTHILLS. THESE STORMS
ARE PRODUCING FREQUENT LIGHTNING, LOCALLY HEAVY RAIN, AND HAIL
ANYWHERE FROM THE SIZE OF PEAS TO DIMES PER RADAR SIGNATURES AND
TRAINED WEATHER SPOTTER REPORTS. SHOWERS AND STORMS ARE NOW SPREADING
NORTHWARD TOWARDS ASTORIA, THE LONG BEACH PENINSULA, WILLAPA HILLS
AND PORTLAND/VANCOUVER METRO. NOTE HI-RES MODELS ARE NOT HANDLING THE
EXTENT OF THIS AREA OF CONVECTION WELL, AND POPS AND THUNDER
PROBABILITIES HAD TO BE MANUALLY ADJUSTED UPWARDS TODAY TO BETTER
REFLECT CURRENT OBSERVATIONS. IT DOES APPEAR THERE IS A VERY SUBTLE
500 MB SHORTWAVE HELPING AID FORCING FOR ASCENT, AS WELL AS FAVORABLE
JET STREAK DYNAMICS AS THE AREA CURRENTLY EXPERIENCING CONVECTION IS
UNDER THE LEFT EXIT REGION OF A 250 MB JET MAX. THIS JET MAX IS
FORECAST TO LIFT NORTHWARD OVER SOUTHWEST WA LATER THIS MORNING IN AN
ENVIRONMENT FEATURING SUBSTANTIAL MID-LEVEL INSTABILITY/MOISTURE,
SUGGESTING THE AREA OF ONGOING CONVECTION WILL LIKELY CONTINUE
LIFTING NORTHWARD. WILL ALSO NOTE ANY LOCATION IS NORTHWEST OR AND
SOUTHWEST WA IS FAIR GAME TO SEE SHOWERS AND STORMS TODAY AND
TONIGHT, NOT SOLELY THE LOCATIONS THAT HAVE BEEN MENTIONED ABOVE.
CHANCES FOR SHOWERS REMAIN IN THE FORECAST SUNDAY AND SUNDAY NIGHT,
WITH THE HIGHEST PROBABILITIES OVER THE CASCADES. THUNDERSTORM
CHANCES PLUMMET BELOW 10-15% ON SUNDAY, WHICH SEEMS REASONABLE AS THE
LREF MEAN SHOWS MUCAPE VALUES FALLING BELOW 100 J/KG AS MID-LEVEL
LAPSE RATES BECOME LESS STEEP PER BUFKIT SOUNDINGS. THE MAIN
EXCEPTION TO THAT IS OVER THE LANE AND LINN COUNTY CASCADES WHERE
THERE APPEARS TO BE A BIT MORE INSTABILITY WITH SLIGHTLY HIGHER
CHANCES FOR THUNDERSTORMS. -TK
LONG TERM...MONDAY THROUGH FRIDAY NIGHT
A COOL, WET AND SHOWERY
FALL-LIKE WEATHER PATTERN DEVELOPS MONDAY AND CONTINUES THROUGH
AT LEAST TUESDAY IN RESPONSE TO A CLOSED UPPER LEVEL LOW THAT IS SET
TO SETTLE OVER THE REGION DURING THAT TIME. THIS LOW WILL BRING
WIDESPREAD SHOWERS WITH SIGNIFICANT RAIN AMOUNTS FOR THIS TIME OF
YEAR. THE NBM CONTINUES TO SHOW HIGH PROBABILITIES FOR AT LEAST
0.25-0.5" OF RAIN OVER ALL OF NORTHWEST OR AND SOUTHWEST WA FROM THE
COAST TO THE CASCADES, RANGING FROM 60-90% FOR THE 48-HOUR PERIOD
ENDING AT 5 AM WEDNESDAY, EXCEPT 40-70% OVER SOUTHWEST WASHINGTON.
NOTE THE HIGHEST PROBABILITIES ARE OVER THE OREGON CASCADES, WHICH
WILL HELP DAMPEN ONGOING WILDFIRE ACTIVITY. WITH THE CLOUDY/SHOWERY
CONDITIONS IN PLACE, HIGH TEMPERATURES WILL BE WELL BELOW NORMAL,
LIKELY ONLY IN THE UPPER 60S TO LOWER 70S.
THE FORECAST BECOMES MORE UNCERTAIN FROM WEDNESDAY ONWARD, ESPECIALLY
IN REGARDS TO THE EXACT LOCATION OF THE AFOREMENTIONED UPPER LOW AT
THAT POINT IN TIME, WHICH WILL ULTIMATELY IMPACT PRECIPITATION
CHANCES, CLOUD COVER, AND TEMPERATURES. WILL NOTE THERE ARE CHANCES
FOR SHOWERS WEDNESDAY THROUGH FRIDAY, HOWEVER CHANCES ARE HIGHEST ON
WEDNESDAY AT 40-60%. CHANCES FOR SHOWERS DECREASE TO 20-30% FOR
THURSDAY AND FRIDAY. IF SHOWERY WEATHER DOES OCCUR, EXPECT
TEMPERATURES TO REMAIN COOLER THAN AVERAGE. IF CONDITIONS TREND DRY
WITH BREAKS OF SUN, TEMPERATURES WOULD MOST LIKELY REBOUND WELL INTO
THE 70S. -TK
AVIATION
ALONG THE COAST IFR/LIFR CEILINGS ARE EXPECTED TO
CONTINUE FOR THE MAJORITY OF THE TAF PERIOD, LIKELY LIFTING TO
MVFR/VFR AGAIN AFTER 19-22Z SAT FOR A SHORT PERIOD OF TIME BEFORE
CONDITIONS DEGRADE AGAIN 00-04Z SUN. ONSHORE FLOW WILL PUSH
STRATUS INLAND THROUGH COAST RANGE GAPS AND ALONG THE COLUMBIA
RIVER INTO THE MORNING HOURS AS WELL. THERE'S A 60-80% CHANCE OF
MVFR CEILINGS AT MOST INLAND TERMINALS, EXCEPT FOR 80-90% CHANCE
AT KEUG/KTTD, BEGINNING BETWEEN 09-14Z SAT. CONDITIONS INLAND
EXPECTED TO LIFT TO VFR AFTER 19-21Z SAT ALTHOUGH CONFIDENCE
REGARDING THE EXACT TIMING OF THIS IMPROVEMENT IS ONLY MODERATE.
ADDITIONALLY, AS OF 9-10Z THIS MORNING THERE IS ANOTHER ROUND OF
ONGOING HIGH-BASED (AOA 7-8KFT+) THUNDERSTORM ACTIVITY MOVING
SOUTHEAST TO NORTHWEST ACROSS THE CENTRAL/SOUTHERN WILLAMETTE
VALLEY THROUGH THE COAST RANGE. UNFORTUNATELY HIGH-RESOLUTOIN
GUIDANCE HAS BEEN SUB-PAR ATTEMPTING TO RESOLVE THUNDERSTORM
PLACEMENT TONIGHT ALTHOUGH THE TREND IS FOR THE AXIS OF ACTIVITY
TO SLOWLY SHIFT NORTH-NORTHWEST TOWARDS THE PORTLAND METRO INTO
THE EARLY TO MID MORNING HOURS. WE'LL POTENTIALLY GET A DEFINED
LULL IN SHOWERS/STORMS AFTER ~13-15Z SAT BEFORE ADDITIONAL
SCATTERED SHOWERS AND THUNDERSTORMS REGENERATE 20-23Z SAT. WHILE
MODELS INDICATE STORMS WILL BEGIN OVER THE CASCADES, THERE IS
DECENT POTENTIAL FOR THEM TO PUSH INTO THE WILLAMETTE VALLEY AND
SW WASHINGTON. HOWEVER, CONFIDENCE IN PLACEMENT/TIMING OF THE
SECOND ROUND REMAINS MUCH TOO LOW TO INCLUDE TAFS, BUT WILL
CONTINUE TO EVALUATE. BRIEF PERIODS OF HEAVY RAIN COULD RESULT IN
MVFR/IFR CONDITIONS.
PDX AND APPROACHES...MVFR CONDITIONS ARE IMMINENT THIS MORNING
WITH THE ASOS ALREADY REPORTING FEW-SCT 1-2KFT AND NEARBY KTTD
DROPPING TO MVFR AS OF 0930Z. WE'LL NEED TO WATCH ONGOING
CONVECTION HEADED INTO THE SUNRISE HOURS AS THERE IS A 20-30%
CHANCE FOR AN ISOLATED THUNDERSTORM IN THE VICINITY OF THE AIRPORT
CONDITIONS PRIOR TO ~14Z - RADAR IS INDICATING ACTIVITY IS
STARTING TO GENERATE SOUTH TERMINAL. HEADED INTO THE MIDDAY HOURS
AND EARLY AFTERNOON EXPECT CLEARING BACK VFR. THEN AS THE
AFTERNOON PROGRESSES WE'LL ONCE AGAIN HAVE TO BE ON THE LOOKOUT
FOR THUNDERSTORM ACTIVITY MOVING IN FROM THE SOUTH- SOUTHEAST,
ALTHOUGH CONFIDENCE IN PLACEMENT/TIMING IS LOW FOR KPDX. -SCHULDT
MARINE
AN AREA OF LOW PRESSURE IS EXPECTED TO PROGRESSES
THROUGH THE WATERS THIS WEEKEND ALLOWING FOR A SWITCH TO SOUTHERLY
WINDS AS THROUGH THE WATERS THIS WEEKEND, WHICH WILL FACILITATE A
SWITCH TO SOUTH TO SOUTHWEST WINDS BY THE AFTERNOON HOURS ALBEIT
FAIRLY LIGHT OVERALL. WE'LL CONTINUE TO HAVE TO WATCH FOR SLIGHT
CHANCES (15-20%) FOR THUNDERSTORMS THROUGH TODAY AS WELL. EXPECT
THESE SOUTHERLY WINDS TO PERSIST THROUGH MONDAY AND TUESDAY BEFORE
TURNING NORTHERLY AGAIN ON WEDNESDAY AS THE LOW PRESSURE MOVES
OFF TO THE EAST AND SURFACE HIGH PRESSURE RETURNS TO THE WATERS.
SEAS WILL GENERALLY HOLD IN THE 3-5 FT RANGE INTO EARLY NEXT WEEK.
THERE IS A 30-40% CHANCE OF COMBINED SEAS CLIMBING ABOVE 5 FT
DURING THE MIDDLE NEXT WEEK WITH THOSE PROBABILITIES CLIMBING TO
60-75% BY THE END OF NEXT WEEK. -SCHULDT
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
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