599
FXUS66 KPQR 201803 AAA
AFDPQR
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
1100 AM PDT THU AUG 20 2026
UPDATED AVIATION DISCUSSION...
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 18Z FRIDAY
MARINE STRATUS THAT PUSHED INTO
THE COAST EARLY THIS MORNING HAS BEGUN TO BURN OFF. AS A RESULT,
EXPECT STRATUS TO BREAK OUT AT KAST AND IMPROVE TO VFR AROUND
20-21Z THU. THERE IS LESS CONFIDENCE FOR IMPROVEMENT TO VFR AT
KONP, WITH GUIDANCE SUGGESTING A 30-50% CHANCE OF MVFR CIGS
THROUGH THE AFTERNOON. REGARDLESS, LIFR/IFR STRATUS WILL RETURN TO
COASTAL TERMINALS AROUND 00-03Z FRI AND PERSIST OVERNIGHT. AS FOR
THE WILLAMETTE VALLEY, VFR CONDITIONS AND CLEAR SKIES WILL
PREVAIL THROUGH THE TAF PERIOD. OTHERWISE, EXPECT WEST/NORTHWEST
WINDS UNDER 10 KT TO SHIFT WESTERLY TO SOUTHWESTERLY AROUND 06-12Z
FRI.
KPDX AND APPROACHES...PREDOMINATELY VFR WITH CLEAR SKIES THROUGH
THE TAF PERIOD. NORTHWEST WINDS 3-6 KT SHIFTING WESTERLY AROUND
12Z FRI.~12
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.
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