633
FXUS66 KPQR 051804 AAA
AFDPQR
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
1104 AM PDT TUE AUG 5 2025
UPDATED AVIATION DISCUSSION.
SYNOPSIS
MEAN TROUGHING WILL BRING CONTINUED BELOW-NORMAL
TEMPERATURES THROUGH THURSDAY WITH CLOUDS AND CHANCES FOR A
WIDESPREAD WETTING RAIN SPREADING FROM WEST TO EAST TUESDAY
NIGHT INTO WEDNESDAY. BUILDING HIGH PRESSURE WILL BRING A
WARMING AND DRYING TREND THURSDAY THROUGH THE WEEKEND AND
POTENTIALLY HAZARDOUS HEAT BY EARLY NEXT WEEK.
SHORT TERM...NOW THROUGH THURSDAY NIGHT
WHILE LARGE-SCALE
TROUGHING PERSISTS OVER THE NORTHEAST PACIFIC, HEIGHTS BRIEFLY
RISING ALOFT BEHIND A DEPARTING SHORTWAVE WILL SEE A SLIGHT
MODERATION IN TEMPERATURES UP TOWARD SEASONAL NORMS TODAY. AS
MORNING HIGH CLOUDS EXIT EASTWARD, PERIODS OF SUNSHINE AND
SOUTHERLY TO SOUTHWESTERLY LOW-LEVEL FLOW WILL PUSH AFTERNOON
HIGHS ABOVE 80 DEGREES WITHIN INLAND VALLEYS, WHILE ONSHORE FLOW
KEEPS COASTAL AREAS IN THE 60S TO LOW 70S. ADDITIONAL CLOUD
COVER WILL ARRIVE THROUGH THE AFTERNOON AHEAD OF AN APPROACHING
FRONTAL SYSTEM, KEEPING TEMPERATURES RELATIVELY MILD OVERNIGHT
TONIGHT IN THE MID 50S TO MID 60S ACROSS THE REGION.
AS AN UPPER CUTOFF LOW OVER SOUTHEASTERN ALASKA TRACKS TOWARD
THE NORTHERN WASHINGTON CASCADES, A WEAK SURFACE LOW OFFSHORE OF
VANCOUVER ISLAND WILL OCCLUDE AND FILL AS IT MOVES BENEATH THE
UPPER LOW. A PAIR OF SURFACE FRONTS EXTENDING SOUTHWARD FROM
THE SURFACE LOW WILL BRING PERIODS OF RAIN ALONG THE COAST THIS
EVENING INTO TONIGHT, AND TO INLAND AREAS INTO BY WEDNESDAY
MORNING. CAM GUIDANCE SUGGESTS AN INITIAL PERIOD OF STEADIER
STRATIFORM RAIN AS THE MAIN UPPER SHORTWAVE PASSES OVERHEAD,
FOLLOWED BY A MORE SHOWERY DISTRIBUTION WITH DECREASING COVERAGE
OF RAIN THROUGH WEDNESDAY AFTERNOON. WITH ANY INSTABILITY
BENEATH THE UPPER LOW LIKELY DISPLACED WELL TO THE NORTH,
THUNDER IS UNLIKELY BUT CANNOT BE COMPLETELY RULED OUT ALONG THE
SOUTHERN WASHINGTON CASCADES ON WEDNESDAY AFTERNOON. LINGERING
POST-FRONTAL SHOWERS MAY CONTINUE INTO THURSDAY MORNING BEFORE
SEASONABLY COOL AND DRY WEATHER RETURNS THURSDAY AFTERNOON INTO
THURSDAY NIGHT.
ABUNDANT MOISTURE ASSOCIATED WITH THIS SYSTEM, AS EVIDENCED BY
PRECIPITABLE WATER VALUES APPROACHING 1.5 INCHES ACROSS THE
REGION, HAS SEEN RAINFALL AMOUNTS TREND SLIGHTLY HIGHER IN THE
MOST RECENT NUMERICAL GUIDANCE. THE HIGHEST TOTALS REMAIN
ACROSS THE WILLAPA HILLS AND MOUNT ST. HELENS VICINITY, WITH
GREATER THAN 50% CHANCES OF EXCEEDING 0.5" OF RAIN ALONG THE
HIGHEST TERRAIN. ACCUMULATIONS OF 0.25" OR MORE ARE EXPECTED
ALONG THE COAST AND COAST RANGE FROM TILLAMOOK COUNTY NORTHWARD,
AS WELL AS LOWLANDS ACROSS SOUTHWESTERN WASHINGTON AND THE
LOWER COLUMBIA EASTWARD THROUGH THE PORTLAND/VANCOUVER METRO.
LESSER AMOUNTS ARE EXPECTED TO THE SOUTH, AROUND 0.1" FOR THE
REMAINDER OF THE CENTRAL OREGON COAST AND CENTRAL WILLAMETTE
VALLEY, AND 0.05" OR LESS IN THE SOUTHERN WILLAMETTE VALLEY AND
WESTERN SLOPES OF THE CENTRAL OREGON CASCADES. -PICARD
LONG TERM...FRIDAY THROUGH MONDAY
A MARKED PATTERN SHIFT WILL
SEE RISING HEIGHTS ALOFT ATOP RESURGENT SURFACE HIGH PRESSURE
OVER THE NORTHEAST PACIFIC THROUGH THE WEEKEND, USHERING IN A
STEADY WARMING AND DRYING TREND. NEAR-NORMAL TEMPERATURES ON
FRIDAY WILL RISE TO POTENTIALLY HAZARDOUS LEVELS IN THE MID TO
UPPER 90S ACROSS INLAND AREAS BY SUNDAY AND MONDAY, WHILE
DEWPOINT TEMPERATURES RISING INTO THE LOW 60S WILL ALSO MAKE
CONDITIONS FEEL NOTICEABLY HUMID. VERY MILD OVERNIGHT LOWS IN
THE MID TO UPPER 60S ARE MOST LIKELY IN THE CENTRAL WILLAMETTE
VALLEY, PORTLAND/VANCOUVER METRO, LOWER COLUMBIA AND COWLITZ
VALLEYS, AND THROUGH THE COLUMBIA RIVER GORGE SUNDAY AND MONDAY
NIGHTS, YIELDING INCREASED COVERAGE OF MAJOR HEATRISK. A LACK
OF SUFFICIENT OVERNIGHT COOLING CAN RAISE THE CUMULATIVE HEAT
STRESS AND ELEVATE THE RISK FOR HEAT ILLNESS. RESIDENTS OF THE
AFOREMENTIONED AREAS WITHOUT ACCESS TO ADEQUATE COOLING SHOULD
BEGIN TO PLAN FOR THIS PERIOD OF HAZARDOUS HEAT. -PICARD
AVIATION
VFR THROUGH THE EARLY AFTERNOON, BUT AN INCOMING FRONT
WILL CAUSE A DRASTIC SHIFT IN CONDITIONS. SATELLITE SHOWS THE
STRATUS AHEAD OF THE SYSTEM IS JUST OFFSHORE BUT WILL MOVE IN
THROUGH THE DAY. IN ADDITION, RAINFALL IS EXPECTED BECOMING
LOCALLY HEAVIER AT TIMES. COASTAL TERMINALS, AND INLAND SITES
NORTH OF KSLE WILL SEE THE HIGHEST RAINFALL RATES AND THUS
VISIBILITY WILL EXPERIENCE THE GREATEST REDUCTION. EXPECTING IFR
CONDITIONS (BOTH CIG AND VIS) FROM TILLAMOOK NORTHWARD ALONG THE
COAST, AND FROM KPDX NORTHWARD. REGARDING INLAND TERMINALS,
CONFIDENCE IS LOW IN THE TIMING, AND WHETHER OR NOT REDUCTION OF
VIS/CIGS WILL OCCUR. HOWEVER, THERE IS A HIGH PROBABILITY (GREATER
THAN 75%) FOR THE COAST.
PDX AND APPROACHES...VFR THROUGH THE NEXT 15-18 HOURS AHEAD OF AN
INCOMING FRONT. CIGS AND VIS WILL BE UNAFFECTED DURING THAT TIME,
BUT WILL SEE A DRASTIC REDUCTION TO MVFR LEVELS WITH THE FRONTAL
PASSAGE. EARLIEST ARRIVAL OF RAIN IS 05Z WED, WITH THE LATEST
BEING AROUND 12Z WED. HAVE TRENDED TOWARDS A GRADUAL REDUCTION IN
CIGS. UNLESS A HEAVY SHOWER ESTABLISHES ITSELF RIGHT OVER KPDX,
VIS SHOULD BE UNAFFECTED. -MUESSLE
MARINE
A LOW PRESSURE SYSTEM DROPS SOUTH INTO HAIDA GWAII
TODAY, BRINGING A SOUTHERLY WIND REVERSAL THROUGH WEDNESDAY
MORNING. WINDS WILL BE SOUTHERLY TO SOUTHWESTERLY 10-15 KT WITH
GUSTS AS HIGH AS 20 KT ALONG THE COAST AND THE FAR OUTER WATERS
THROUGH THIS EVENING. DUE TO THE LOCATION OF THE LOW, WIND GUSTS
SHOULD REMAIN BELOW 25 KT. SEAS WILL INCREASE TO 5 TO 7 FT BY
THIS EVENING AND WILL REMAIN SO THROUGH AT LEAST THURSDAY.
NORTHWESTERLY FLOW THEN RETURNS EARLY THURSDAY. THE NEXT PERIOD
OF POTENTIALLY ACTIVE MARINE CONDITIONS WILL BE ON FRIDAY
AFTERNOON. -HALL/MUESSLE
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
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