573
FXUS66 KPQR 201007
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
307 AM PDT THU AUG 20 2026
SYNOPSIS
DRY AND VERY WARM CONDITIONS TODAY. LOW PRESSURE
BRINGS CHANCES FOR SHOWERS FRIDAY EVENING INTO SATURDAY ACROSS
NORTHWEST OREGON AND SOUTHWEST WASHINGTON, WITH A 15% CHANCE
FOR THUNDERSTORMS OVER THE CASCADES AND 5-10% CHANCE ELSEWHERE.
WINDS OUT OF THE NORTH/NORTHWEST TODAY, SHIFTS TO THE
WEST/SOUTHWEST ON FRIDAY. SEASONABLE WEATHER RETURNS SUNDAY
THROUGH THE MIDDLE OF NEXT WEEK.
DISCUSSION...TODAY THROUGH WEDNESDAY
DRY AND VERY WARM
WEATHER CONTINUES TODAY AS AN UPPER-LEVEL RIDGE AMPLIFIES OVER
THE ROCKIES AND GREAT BASIN. LOCATIONS WITH MORNING CLOUDS
SHOULD GRADUALLY CLEAR OUT BY THE AFTERNOON AS DAYTIME HEATING
PROGRESSES. GIVEN THE STRONGER HIGH PRESSURE TODAY, AFTERNOON
TEMPERATURES ACROSS INLAND VALLEYS ARE FORECAST TO PEAK IN THE
LOW 90S, WHICH IS SLIGHTLY WARMER THAN YESTERDAY. ALONG THE
COAST, ONSHORE FLOW WILL MAINTAIN MILD CONDITIONS WITH HIGHS IN
THE UPPER 60S TO LOW 70S. TONIGHT INTO FRIDAY MORNING, LOW
TEMPERATURES AROUND 60-65 DEGREES ACROSS THE PORTLAND/VANCOUVER
METRO, COLUMBIA RIVER GORGE, AND CASCADE FOOTHILLS WILL RESULT
IN LIMITED OVERNIGHT RELIEF FROM THE HEAT. CHANCES FOR LOW
TEMPERATURES REMAINING ABOVE 65 DEGREES ARE AROUND 15-25% FOR
THE PORTLAND/VANCOUVER METRO AND 60-80% ALONG THE COLUMBIA
GORGE.
THE POTENTIAL FOR LIMITED OVERNIGHT RELIEF IN ADDITION TO THE
AFTERNOON HEAT WILL RESULT IN MODERATE HEATRISK TODAY ALONG
PORTIONS OF THE I-5 CORRIDOR AND COLUMBIA GORGE. THIS MEANS THAT
THIS LEVEL OF HEAT WILL AFFECT THOSE SENSITIVE TO HEAT,
ESPECIALLY THOSE WITHOUT ADEQUATE COOLING OR HYDRATION.
ON FRIDAY, AN UPPER-LEVEL TROUGH OVER THE NORTHEAST PACIFIC
WILL PROGRESS TOWARD THE PACIFIC NORTHWEST, BRINGING SLIGHTLY
COOLER TEMPERATURES, INCREASED CLOUD COVER, AND INCREASING
CHANCES OF PRECIPITATION. GUIDANCE HAS THIS TROUGH SWINGING
INLAND BY FRIDAY NIGHT INTO SATURDAY. THIS UPPER-LEVEL PATTERN
LOOKS LIKE A TYPICAL SET-UP FOR THUNDERSTORM CHANCES, AT LEAST
OVER THE CASCADES. SOUTHERLY FLOW ALOFT WILL BRING INCREASED
MOISTURE AND INSTABILITY INTO THE MID-LEVELS OF THE ATMOSPHERE
(5-10 KFT). VORTICITY FROM THE UPPER-LEVEL TROUGH WILL ALSO
PROVIDE THE NECESSARY FORCING FOR CONVECTION. THE LATEST
GUIDANCE HAS PRECIPITATION CHANCES BEGINNING OVER THE CASCADES
AFTER 5 PM FRIDAY AT 20-30% CHANCES, WITH 25-40% CHANCES OF
PRECIPITATION SPREADING WEST OF THE CASCADES AFTER 11 PM FRIDAY.
PRECIPITATION CHANCES CONTINUE INTO SATURDAY MORNING, MAINLY
ALONG AND NORTH OF THE OR/WA BORDER. HAVE MAINTAINED A 15%
CHANCE OF THUNDERSTORMS ACROSS THE CASCADES, BUT UNCERTAINTY IS
TOO HIGH FOR THOSE CHANCES TO EXTEND WEST. PWATS AND RH INCREASE
SIGNIFICANTLY WITH THIS MOISTURE, SO IF THUNDERSTORMS DO FORM,
FIRE CONCERNS ARE ON THE LOWER SIDE. OF COURSE, ANY LIGHTNING
THAT STRIKES OUTSIDE OF AREAS THAT HAVE RECEIVED RAIN COULD
CAUSE FIRE STARTS. IT WILL BE IMPORTANT TO MONITOR THE WEATHER
IF YOU HAVE OUTDOOR PLANS FRIDAY AFTERNOON.
ENSEMBLE GUIDANCE SHOWS THE UPPER-LEVEL TROUGH MOVING FURTHER
INTO THE PACIFIC NORTHWEST ON SATURDAY. AS THE ASSOCIATED
SURFACE FRONT MOVES THROUGH, WILL SEE WINDS SHIFT AND COME OUT
OF THE WEST/SOUTHWEST. WINDS WILL INCREASE THROUGH WEST TO EAST
ALIGNED MOUNTAIN GAPS, ESPECIALLY THROUGH THE CENTRAL COLUMBIA
RIVER GORGE INTO HOOD RIVER VALLEY WHERE WINDS COULD GUST TO
25-35 MPH. THERE IS ALSO A 40-60% CHANCE FOR AT LEAST ISOLATED
GUSTS EXCEEDING 40 MPH FOR THESE AREAS, ESPECIALLY FOR HIGHER
TERRAIN AND EXPOSED RIDGETOPS. STRONGER ONSHORE FLOW ACROSS THE
REGION WILL SUPPORT MUCH COOLER TEMPERATURES ON SATURDAY WITH
AFTERNOON HIGHS PEAKING IN THE UPPER 70S.
SUNDAY INTO EARLY NEXT WEEK, MOST ENSEMBLE MEMBERS SUGGEST A
RETURN OF ZONAL FLOW AS THE TROUGH MOVES NORTHEAST INTO
EASTERN WASHINGTON AND CANADA. AS A RESULT, EXPECT TEMPERATURES
TO GRADUALLY REBOUND INTO THE LOW TO MID 80S. GUIDANCE ALSO
INDICATES ANOTHER UPPER-LEVEL TROUGH DROPPING DOWN FROM THE GULF
OF ALASKA AND APPROACHING BRITISH COLUMBIA EARLY NEXT WEEK,
POTENTIALLY IMPACTING THE PACIFIC NW BY MIDWEEK. AT THIS POINT,
THERE STILL REMAINS HIGH UNCERTAINTY WITH THE EXACT MAGNITUDE
AND PLACEMENT OF THE TROUGH NEXT WEEK. HOWEVER, THIS WOULD
SUGGEST THAT ONSHORE FLOW CONTINUES ACROSS THE REGION RESULTING
IN SEASONABLE TEMPERATURES FOR LATE AUGUST. -10/03
AVIATION...THROUGH 06Z FRIDAY
A TYPICAL PATTERN OF MARINE
STRATUS PUSHING INLAND OVERNIGHT IS EXPECTED. ALONG THE COAST,
SATELLITE IMAGERY AND TERMINAL OBSERVATIONS ALREADY SHOW
WIDESPREAD LOW CLOUDS RESULTING IN IFR/LIFR CIGS, WHICH WILL,
WITH HIGH CONFIDENCE, CONTINUE THROUGH AT LEAST 18Z FRI BEFORE
ANY MARGINAL IMPROVEMENTS TO MVFR/VFR. CONFIDENCE IS LOWER IN
THE INLAND PENETRATION OF LOW CLOUDS OVERNIGHT. TERMINALS ALONG
THE LOWER COLUMBIA RIVER (KKLS, KSPB) AND INTO THE PORTLAND AREA
(KPDX, KTTD) WILL HAVE THE HIGHEST CHANCES, 40-60%, OF LOW-END
MVFR CIGS BELOW 2 KFT BETWEEN 12-18Z FRI. CHANCES FOR IFR CIGS
ARE NOT MUCH LOWER: 20-40%. WITHIN THE WILLAMETTE VALLEY, THE
LIKELIHOOD OF MVFR CIGS IS LOWER, 20-40%, WITH PREVAILING VFR
CONDITIONS FAVORED. ANY LOW CLOUDS WILL TEND TO MIX OUT BY
16-18Z FRI. DIURNAL WINDS WILL RISE OUT OF THE NORTH TO
NORTHWEST AT 5-10 KT BY FRIDAY AFTERNOON.
KPDX AND APPROACHES...VFR CONDITIONS FAVORED THROUGH AT LEAST
12Z FRI BEFORE CHANCES FOR MVFR/IFR CIGS INCREASE AS MARINE
STRATUS PENETRATES INLAND ALONG THE COLUMBIA RIVER. ANY CIGS
WILL LIKELY BE AT 2 KFT OR LOWER, WITH NEARLY 50% CHANCES FOR
MVFR CIGS AND 20% FOR IFR. ANY LOW CLOUDS WILL TEND TO MIX OUT
BY 16-18Z FRI. NORTHWEST WINDS EASE BELOW 3 KT TONIGHT, THEN
RISE TO AROUND 5 KT FRIDAY AFTERNOON. -36
MARINE
HIGH PRESSURE WILL CONTINUE TO SUPPORT NORTHERLY WINDS
ACROSS THE WATERS TODAY WITH GUSTS REMAINING BELOW 20 KT. FRIDAY
TO SATURDAY, LOW PRESSURE MOVING OVER THE NORTHEAST PACIFIC WILL
SHIFT WINDS OUT OF THE SOUTH TO SOUTHWEST ACROSS THE WATERS. AS
THE SURFACE FRONT MOVES THROUGH SATURDAY MORNING, THERE IS A
50-80% CHANCE FOR MAXIMUM WIND GUSTS BETWEEN 21 TO 25 KT FOR THE
WATERS NORTH OF CAPE FOULWEATHER, INCLUDING THE COLUMBIA RIVER
BAR. FOR THE REST OF THE WATERS, CHANCES ARE 15-30%.
HIGH PRESSURE AND NORTHERLY WINDS RETURN BY SUNDAY WITH A 40-50%
CHANCE FOR NORTHERLY WIND GUSTS EXCEEDING 21 KTS IN THE AFTERNOON
AND EVENING HOURS WITH THE HIGHEST CHANCES SOUTH OF CAPE FALCON.
SEAS OF 4-6 FT PERSIST THROUGH THE PERIOD. -10
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
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