657
FXUS66 KPQR 251755
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1055 AM PDT THU JUN 25 2026
UPDATED AVIATION DISCUSSION
SYNOPSIS
A SIGNIFICANT WEATHER PATTERN CHANGE BEGINS TODAY
AS A FRONTAL SYSTEM SWINGS THROUGH, BRINGING COOLER TEMPERATURES
AND WIDESPREAD CHANCES FOR RAIN TONIGHT THROUGH SATURDAY. THERE
IS ALSO A 10-15% CHANCE FOR THUNDERSTORMS FRIDAY AFTERNOON AND
A 15-25% CHANCE FOR THUNDERSTORMS SATURDAY AFTERNOON. CONDITIONS
TREND DRIER AND SLIGHTLY WARMER SUNDAY THROUGH EARLY NEXT WEEK,
BUT WE'LL MAINTAIN SLIGHT CHANCES FOR LIGHT RAIN SHOWERS ACROSS
THE COAST RANGE AND CASCADES.
DISCUSSION...TODAY THROUGH WEDNESDAY
TODAY MARKS THE
BEGINNING OF A LARGE-SCALE PATTERN CHANGE TO COOLER AND WETTER
CONDITIONS AS AN UPPER-LEVEL LOW PRESSURE SYSTEM REMAINS ON
TRACK TO PROGRESS INTO THE PACIFIC NORTHWEST FROM THE GULF OF
ALASKA. SATELLITE IMAGERY AS OF EARLY THURSDAY MORNING DEPICTS
WIDESPREAD MARINE STRATUS ALONG THE COAST WITH INCREASING HIGH
LEVEL CLOUDS ACROSS THE BROADER REGION AHEAD OF THIS NEXT
WEATHER SYSTEM.
TEMPERATURES WILL COOL TO NEAR NORMAL WITH MID 70S ACROSS THE
INTERIOR LOWLANDS. HIGH RESOLUTION MODEL GUIDANCE HAS RAINFALL
VIA A COLD-FRONTAL BOUNDARY REACHING THE COAST BY LATE THIS
AFTERNOON/EVENING AND THEN SPREADING INTO THE I-5 CORRIDOR BY
LATE TONIGHT INTO FRIDAY MORNING. WE'LL REMAIN IN THIS COOLER
AND WET PATTERN THROUGH AT LEAST SATURDAY, BUT AT LEAST TOTAL
RAIN AMOUNTS AT THIS TIME APPEAR BENEFICIAL AND GENERALLY NON-
IMPACTFUL. LOOKING AT THE LATEST NBM, CHANCES FOR 48-HOUR RAIN
AMOUNTS EXCEEDING 1 INCH FROM 5 PM THURSDAY TO 5 PM SATURDAY
HAS FALLEN SLIGHTLY SINCE YESTERDAY FOR LOCATIONS WEST OF THE
CASCADES: 30-60% FOR THE COAST AND COAST RANGE, 5-15% ALONG AND
EAST OF THE I-5 CORRIDOR. MEANWHILE, CHANCES REMAIN AROUND
70-80% OR HIGHER ACROSS THE CASCADES DUE TO WESTERLY FLOW
BRINGING OROGRAPHIC ENHANCEMENT. WILL NOTE THAT THE WESTERN-MOST
PARTS OF THE WILLAMETTE VALLEY (WEST OF I-5 INCLUDING
MCMINNVILLE AND CORVALLIS) HAVE A LESS THAN 5% CHANCE OF
EXCEEDING 1 INCH DURING THIS TIMEFRAME DUE TO POTENTIAL
RAINSHADOWING FROM THE COAST RANGE. THE DECREASE IN THESE
CHANCES FOR 1 INCH OF RAIN MAY BE DUE TO THE FACT THAT WE'RE IN
SUCH A DRY AIR MASS. THIS DRY AIR MASS MAY SACRIFICE SOME OF
THE INITIAL RAIN BEFORE THE ATMOSPHERE BECOMES COMPLETELY
SATURATED ENOUGH FOR RAIN TO HIT THE GROUND.
BY FRIDAY AFTERNOON, THE UPPER-LEVEL TROUGH CONTINUES TO MOVE
SOUTH AND EVENTUALLY CENTERS ITSELF RIGHT OVER-TOP THE PACIFIC
NORTHWEST AS A CLOSED LOW ON SATURDAY. TEMPERATURES WILL FURTHER
COOL ALOFT ALLOWING FOR INCREASING ATMOSPHERIC INSTABILITY
DURING THE DAYTIME HOURS AND FACILITATING CAPE VALUES OF 50-100
J/KG FRIDAY AFTERNOON FOR SW WASHINGTON AND THE
PORTLAND/VANCOUVER METRO, AND 100-200 J/KG LATE SATURDAY
MORNING INTO THE AFTERNOON ACROSS THE ENTIRE AREA. THIS
INSTABILITY PLUS SUFFICIENT LIFT FROM THE LOW WILL SUPPORT A
10-15% CHANCE FOR HEAVY SHOWERS AND THUNDERSTORMS ACROSS NW
OREGON AND SW WASHINGTON FRIDAY AFTERNOON, AND A 15-25% CHANCE
FOR THUNDERSTORMS SATURDAY AFTERNOON. FOR NOW, ANY CONVECTION
APPEARS RATHER WEAK AND UNORGANIZED (OUR TYPICAL POST-FRONTAL
POP-UP STORMS). HIGH RESOLUTION GUIDANCE SUGGESTS EFFECTIVE
SHEAR REMAINS BELOW 35 KT; THEREFORE, CHANCES THESE
THUNDERSTORMS BECOME SEVERE ARE UNLIKELY (<5%). OTHERWISE, ANY
STRONG SHOWER OR PASSING THUNDERSTORMS MAY PRODUCE BRIEF HEAVY
RAIN, GUSTY AND ERRATIC WINDS, AND A FEW LIGHTNING STRIKES. ALSO
CAN'T RULE OUT A COLD AIR FUNNEL CLOUD OR TWO GIVEN THE TIME OF
YEAR, ESPECIALLY ON SATURDAY.
THE LATTER HALF OF THE WEEKEND INTO EARLY NEXT WEEK, THE
MAJORITY OF ENSEMBLE MEMBERS ARE SHOWING THE BROADER UPPER-
LEVEL LOW FEATURE SHIFTING EASTWARD AND LINGERING ALONG THE
INTERIOR MOUNTAIN WEST, RETURNING RELATIVELY DRIER CONDITIONS
AND A WARM-UP OF A FEW DEGREES TO OUR AREA. THIS WILL PUT HIGH
TEMPERATURES JUST BELOW THE SEASONAL NORMALS WITH LOW 70S FOR
THE INTERIOR LOWLANDS AND UPPER 50S TO LOW 60S FOR THE COAST).
WILL STILL MAINTAIN PRECIPITATION CHANCES ACROSS THE COAST RANGE
AND CASCADES AS WESTERLY FLOW CONTINUES TO SUPPORT OROGRAPHIC
ENHANCEMENT OF PRECIPITATION, THOUGH ANY ADDITIONAL RAIN AMOUNTS
APPEAR VERY LIGHT. STILL, WE'LL HAVE TO KEEP AN EYE ON SUBTLE
SHORTWAVE FEATURES ROTATING INTO THE REGION NORTH TO SOUTH ON
THE BACK SIDE OF THE UPPER-LEVEL LOW WHICH MAY EXPAND THE
COVERAGE OF SHOWERS TEMPORARILY - LOW CONFIDENCE ON THE
PLACEMENT/TIMING OF THESE SMALLER SHORTWAVE FEATURES. ENSEMBLE
MEMBERS THEN SUGGEST ANOTHER UPPER-LEVEL TROUGH DROPPING DOWN
INTO THE AREA ON WEDNESDAY, HOWEVER, THERE IS ALSO VERY HIGH
UNCERTAINTY WITH HOW MUCH PRECIPITATION WE GET, IF ANY. WESTERLY
WINDS THROUGHOUT THE WEEK WILL BE BREEZIEST ALONG THE CENTRAL
COLUMBIA RIVER GORGE AND ACROSS UPPER HOOD RIVER VALLEY, WITH
CHANCES FOR ISOLATED WIND GUSTS EXCEEDING 45 MPH AROUND 10-35%
FROM FRIDAY THROUGH EARLY NEXT WEEK, WITH THE HIGHEST CHANCES
FROM SUNDAY TO TUESDAY. -10/03/99
AVIATION
LATE THIS MORNING COASTAL TERMINALS CONTINUE TO
FLUCTUATE BETWEEN LOW-END MVFR AND IFR AS STRATUS REMAINS LOCKED
IN PLACE. PROBABILITIES FOR IFR CONDITIONS WILL DECREASE OVER THE
NEXT SEVERAL HOURS BUT REMAIN BETWEEN 10-40%, HIGHEST AROUND KONP.
BEYOND A SLIGHT TREND TO MVFR, EXPECT LITTLE CHANGE THE REMAINDER
OF THE DAY. FOR INLAND TERMINALS, PREDOMINATELY VFR CONDITIONS
INTO THE EVENING HOURS AS CIGS GRADUAL FALL. AFTER 00-04Z FRI,
RAIN STARTS AT THE COAST AND GRADUALLY SPREADS INLAND THROUGHOUT
THE EVENING. AT THE SAME TIME, CIGS WILL DROP TO LOW-END VFR FOR
INLAND TERMINALS WITH A 15-40% CHANCE FOR MVFR CIGS AT ANY GIVEN
HOUR THROUGH 12Z FRI BEFORE THESE PROBABILITIES INCREASE TO
40-60%. WINDS GAIN A SOUTHERLY COMPONENT THIS AFTERNOON AND
INCREASING NEAR 10 KT WITH GUSTS UP TO 20 KT AT KONP.
KPDX AND APPROACHES...VFR CONDITIONS CONTINUE INTO THE EVENING AS
CIGS SLOWLY DECREASE. LOW-END VFR CIGS DEVELOP THIS EVENING AS
THE FRONTAL SYSTEM MOVES IN AND BRINGS RAIN. 10-40% CHANCE FOR
MVFR CIGS AT ANY GIVEN HOUR BETWEEN 05-12Z FRI BEFORE THEY POP TO
60-70%. -99/10
MARINE
HIGH PRESSURE WILL MAINTAIN NORTHWEST WINDS ACROSS
THE COASTAL WATERS THROUGH EARLY THIS MORNING. WINDS ARE
GENERALLY EXPECTED TO REMAIN UNDER 20 KT. WEAKENING HIGH
PRESSURE WILL GIVE WAY TO A FRONTAL SYSTEM APPROACHING THE AREA
ON TODAY. WINDS ARE EXPECTED TO BACK WEST TO SOUTHWESTERLY
THURSDAY AFTERNOON BEFORE THE COLD FRONT PUSHES ACROSS THE
COASTAL WATERS THURSDAY NIGHT INTO FRIDAY. AS THE FRONT MOVES
IN, PRESSURE GRADIENTS WILL TIGHTEN AND RESULT IN BRIEF SMALL
CRAFT CONDITIONS WITH SOUTHERLY WIND GUSTS UP TO 25 KT ACROSS
THE INNER COASTAL WATERS NORTH OF CAPE FOULWEATHER AND UP TO 10
NM OFFSHORE. THEREFORE, A SMALL CRAFT ADVISORY HAS BEEN ISSUED
FOR THESE WATERS INCLUDING THE COLUMBIA RIVER BAR BETWEEN FROM
11 PM THURSDAY TO 5 AM FRIDAY.
WEST TO NORTHWEST WINDS WILL PERSIST BEHIND THE FRONT LATER
FRIDAY AND INTO SATURDAY AS WEAK LOW PRESSURE LINGERS NEAR
VANCOUVER ISLAND. HIGH PRESSURE GRADUALLY BUILDS ACROSS THE
WATERS LATE WEEKEND. SEAS AROUND 4 TO 5 FT THROUGH FRIDAY
BUILD TO AROUND 7 TO 9 FT THIS WEEKEND AS A WEST-NORTHWESTERLY
SWELL MOVES THROUGH THE WATERS. -10/DH
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 5 AM PDT
FRIDAY FOR PZZ210-251-252.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
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