294
FXUS66 KPQR 201034
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
234 AM PST TUE JAN 20 2026
SYNOPSIS
HIGH PRESSURE AND DRY WEATHER CONTINUES THROUGH AT
LEAST THE END OF THE WEEK WITH BREEZY EASTERLY WINDS THROUGH
THE COLUMBIA RIVER GORGE AND EASTERN PORTLAND/VANCOUVER METRO.
AS LONG AS HIGH PRESSURE PREVAILS, CLEAR SKIES AND LIGHT WINDS
AWAY FROM THE COLUMBIA GORGE WILL RESULT IN FROST AND/OR
FREEZING FOG FORMATION ACROSS MOST INTERIOR LOWLAND VALLEYS.
NEAR/BELOW FREEZING TEMPERATURES IN COMBINATION WITH ANY FOG MAY
LEAD TO LOCALLY SLICK ROAD CONDITIONS. LOWER CONFIDENCE FOR
FOG/FROST FOR LOCATIONS THAT REMAIN WINDY AND/OR HAVE PERSISTENT
STRATUS. CHANCES FOR PRECIPITATION RETURN THIS WEEKEND, BUT
DETAILS ON THE EXACT TIMING AND IMPACTS REMAIN NEBULOUS.
DISCUSSION...TUESDAY MORNING THROUGH MONDAY
SATELLITE IMAGERY
AS OF 2 AM TUESDAY SHOWS MOSTLY CLEAR SKIES ACROSS NW OREGON AND
SW WASHINGTON EXCEPT FOR A FEW PATCHES OF FOG/LOW STRATUS IN THE
SOUTHERN WILLAMETTE VALLEY, NORTHERN COWLITZ VALLEY, AND THE
HOOD RIVER VALLEY AND SURROUNDING AREAS. SURFACE OBSERVATIONS
INDICATE TEMPERATURES ARE CURRENTLY NEAR TO BELOW 30 DEGREES
ACROSS MUCH OF THE AREA EXCEPT FOR ALONG THE COAST AS WELL AS
FOR ELEVATIONS BETWEEN 1500 FT TO 5000 FT DUE TO A CONTINUED
STRONG SUBSIDENCE INVERSION UNDER STRONG HIGH PRESSURE. THE LAST
FEW ENSEMBLE RUNS HAVE INDICATED THAT THIS STRONG HIGH PRESSURE
THAT HAS REFUSED TO BUDGE OVER THE WEST COAST/EASTERN PACIFIC
WILL NOW LIKELY STICK AROUND THROUGH AT LEAST SATURDAY, THOUGH
SUBTLE CHANGES TO THE RIDGE OVER THE PACNW WILL LEAD TO SUBTLE
CHANGES TO THE FORECAST BEGINNING THURSDAY.
BETWEEN NOW AND WEDNESDAY, CONDITIONS WILL REMAIN FAIRLY SIMILAR
TO PREVIOUS DAYS. THE CURRENT PATTERN HAS RESULTED IN A
TIGHTENING OF PRESSURE GRADIENTS OVER THE CASCADES, THOUGH THESE
HAVE EASED A BIT COMPARED TO PREVIOUS DAYS. CAMS INDICATE THE
PRESSURE GRADIENT WILL SLACKEN SLIGHTLY IN THE OVERNIGHT AND
EARLY MORNING HOURS EACH DAY BEFORE TIGHTENING AGAIN IN THE LATE
MORNING THROUGH EVENING HOURS, ALLOWING BREEZY EAST WINDS
THROUGH THE COLUMBIA RIVER GORGE INTO THE EASTERN PORTLAND METRO
TO DECREASE THEN INCREASE ACCORDINGLY. CURRENT KPDX TO KDLS
PRESSURE GRADIENT IS AROUND -6 TO -7 MB, AND WIND GUSTS HAVE
DECREASED TO AROUND 20-30 MPH THROUGH THE EASTERN PORTLAND
METRO, INCLUDING TROUTDALE, AND 40-55 MPH FOR WINDER LOCATIONS
EAST OF TROUTDALE. AS PRESSURE GRADIENTS INCREASE TO -7 TO -9 MB
LATER THIS MORNING AND AFTERNOON, PEAK GUSTS WILL LIKELY
INCREASE TO 25-35 MPH IN THE EASTERN PORTLAND METRO AND 45-60+
MPH EAST OF TROUTDALE. RINSE AND REPEAT THROUGH AT LEAST
WEDNESDAY EVENING.
CLEAR SKIES AND LIGHT WINDS AWAY FROM THE WINDS FROM THE
COLUMBIA RIVER GORGE WILL LEAD TO EFFICIENT RADIATIONAL
COOLING ACROSS THE AREA EACH NIGHT THROUGH THE END OF THE WEEK,
CONTINUING TO DROP OVERNIGHT LOWS TO NEAR OR BELOW FREEZING
ACROSS THE WILLAMETTE VALLEY, SOUTHWEST WASHINGTON LOWLANDS, AND
UPPER HOOD RIVER VALLEY. THESE ARE FAVORABLE CONDITIONS FOR
WIDESPREAD FROST DEVELOPMENT, ESPECIALLY OVER GRASSES AND METAL
SURFACES. FREEZING FOG MAY ALSO DEVELOP IN SOME LOCATIONS,
PARTICULARLY ACROSS THE SOUTHERN WILLAMETTE VALLEY AND LOWER
ELEVATIONS OF COWLITZ COUNTY WHERE SURFACE CONDITIONS ARE MORE
MOIST AND PROTECTED FROM THE DRY AIR FILTERING THROUGH THE
CASCADE GAPS. ANY FREEZING FOG THAT DEVELOPS COULD LEAD TO
LOCALLY SLICK ROAD CONDITIONS.
ADDITIONALLY, STAGNANT AIR WILL BE A CONTINUED CONCERN UNDER
THIS SUBSIDENCE INVERSION AS THE WINDS DECREASE, LEADING TO AIR
QUALITY CONCERNS THROUGH AT LEAST MID-WEEK. MIXING HEIGHTS WILL
REMAIN LOW AND TRANSPORT WINDS WILL BE WEAK. THEREFORE, AN AIR
STAGNATION ADVISORY REMAINS IN EFFECT FOR MOST OF THE WILLAMETTE
VALLEY DUE TO THIS CONCERN THROUGH 4 PM WEDNESDAY. THE PORTLAND
METRO AREA FROM THE WEST HILLS EASTWARD WERE NOT INCLUDED IN
THIS ADVISORY DUE TO STRONGER WINDS FROM THE GORGE MAINTAINING A
MORE MIXED ATMOSPHERE.
ON WEDNESDAY INTO THURSDAY, THE MAJORITY OF GFS, EURO, AND
CANADIAN ENSEMBLE MEMBERS AND THEIR DETERMINISTIC MODELS
INDICATE A TROUGH MOVING THROUGH THE CENTRAL PACIFIC THAT WILL
PINCH OFF INTO A CUTOFF LOW AND MOVE TOWARDS CALIFORNIA,
UNDERCUTTING THE RIDGE OF HIGH PRESSURE INSTEAD OF BREAKING IT
DOWN COMPLETELY, THUS LEAVING US IN A DRIER REX BLOCK PATTERN.
HOWEVER, THIS CHANGE WILL CAUSE A SUBTLE SHIFT OF THE RIDGE OFF
OF THE WEST COAST FROM A SLIGHT POSITIVE TILT TO A SLIGHT
NEGATIVE TILT BY FRIDAY. THE SUBSIDENCE INVERSION AND VERY TIGHT
PRESSURE GRADIENTS OVER THE CASCADES ARE LIKELY TO BREAK DOWN
THURSDAY INTO FRIDAY, LEADING TO A MODERATING OF OVERNIGHT
TEMPERATURES IN THE FOOTHILLS AND TERRAIN AS WELL AS THE BREEZY
EAST WINDS THROUGH THE GORGE, THOUGH WEAK OFFSHORE FLOW IS
EXPECTED TO CONTINUE.
UNDER THIS RIDGING, DRY WEATHER IS LIKELY TO CONTINUE THROUGH AT
LEAST SATURDAY. HOWEVER, AROUND 15% OF ENSEMBLE MEMBERS SUGGEST
THE SLIGHT NEGATIVE TILT OF THE HIGH PRESSURE COULD ALLOW FOR A
WEAK SHORTWAVE TO MOVE SOUTH ALONG THE FLOW OVER THE PACNW,
BRINGING A 10-20% CHANCE OF LIGHT SHOWERS TO THE COAST AND
TERRAIN FRIDAY AND SATURDAY. TEMPERATURES ARE LIKELY TO REMAIN
ON THE COLD SIDE, ESPECIALLY IN THE OVERNIGHT HOURS DUE TO A
PUSH OF COLDER ARCTIC AIR FROM THE EAST.
THEN, AROUND 80% OF ENSEMBLE MEMBERS SUGGEST A LOW MOVING
THROUGH THE NE PACIFIC WILL FINALLY BREAK DOWN THE RIDGING
SOMETIME SUNDAY INTO MONDAY, WITH INCREASING CHANCES OF
PRECIPITATION OF AROUND 30-60%. THIS WOULD BE A PRETTY WEAK
SYSTEM BY THE TIME IT MOVES INTO THE PACNW WITH LIMITED
PRECIPITATION ACCUMULATION. HOWEVER, THERE ARE STILL A COUPLE
OF ITEMS TO KEEP EYES ON AS THIS SYSTEM MOVES INLAND. FIRST, IF
THERE IS PRECIPITATION LATE SATURDAY NIGHT INTO SUNDAY MORNING,
A HANDFUL OF ENSEMBLE MEMBERS SUGGEST THAT OVERNIGHT/EARLY
MORNING TEMPERATURES WILL REMAIN COLD ENOUGH TO RESULT IN WET,
NON-IMPACTFUL SNOW OR RAIN/SNOW MIX FALLING DOWN TO THE VALLEY
FLOOR WHEN PRECIPITATION RETURNS. IF THIS OCCURS, IMPACTS WOULD
BE MINIMAL GIVEN AIR TEMPERATURES WILL BE MARGINALLY FREEZING
DUE TO ONSHORE FLOW AND ROADS WOULD BE TOO WARM TO ACCUMULATE
SNOW. SECOND IS PRECIPITATION TYPE IN THE CENTRAL COLUMBIA
RIVER GORGE AND UPPER HOOD RIVER VALLEY AS PRECIPITATION BEGINS.
IF EASTERLY WINDS CONTINUE INTO THE WEEKEND, THEN COLDER AIR
MAY LINGER LONGER FOR THESE AREAS. THIS COULD RESULT IN WINTERY
PRECIPITATION, ESPECIALLY IF THE INCOMING MOISTURE OVERLAPS AT
THE SAME TIME AS THE FREEZING AIR NEAR THE SURFACE. THESE AREAS
CAN REMAIN MUCH COLDER THAN OTHER INTERIOR VALLEYS LIKE THE
WILLAMETTE VALLEY AND SOUTHWEST WA LOWLANDS, AND MODEL GUIDANCE
IS GENERALLY TOO QUICK IN SCOURING OUT THE COLD AIR. SPECIFIC
DETAILS WILL BECOME MORE CLEAR AS WE GET CLOSER TO PRECIPITATION
RETURNING. -03/99
AVIATION
A PERSISTENT UPPER LEVEL RIDGE OVER THE REGION WILL
CONTINUE TO YIELD WIDESPREAD VFR CONDITIONS FOR MOST TERMINALS
THROUGH THE PERIOD. AS OF 10Z TUE, POCKETS OF IFR/LIFR CONDITIONS
WITHIN LOW STRATUS/FOG HAVE REDEVELOPED IN SHELTERED PORTIONS OF
THE SOUTHERN WILLAMETTE AND COWLITZ VALLEYS, AS WELL AS MVFR CIGS
IN VALLEYS EAST OF THE CASCADE CREST INCLUDING AT K4S2. AN
OFFSHORE PRESSURE GRADIENT CONTINUES TO SUPPORT EASTERLY WINDS AT
PORTLAND-AREA AND COASTAL TERMINALS, AND LIGHT NORTHERLY WINDS
ALONG THE WILLAMETTE VALLEY. STRONGER WINDS HAVE EASED WITH THE
PRESSURE GRADIENT WITH GUSTS TO 20-25 KT WILL REMAIN POSSIBLE AT
KTTD AND 45-56 KTS EAST OF KTTD. HOWEVER, THE PRESSURE GRADIENT IS
EXPECTED TO TIGHTEN AGAIN TUESDAY MORNING AFTER 15Z WITH EASTERLY
GUSTS INCREASING TO 25-35 KT AT KTTD AND UP TO 45-60 KT EAST OF
KTTD AT THE WESTERN END OF THE COLUMBIA RIVER GORGE.
KPDX AND APPROACHES...VFR FLYING CONDITIONS EXPECTED THROUGH THE
PERIOD. DIURNAL EAST-SOUTHEAST WINDS AROUND 5 KT WILL INCREASE BY
18-20Z TO AROUND 10-15 KT. -36/03
MARINE
STRONG RIDGING ALOFT CONTINUES TO FAVOR PERSISTENT
OFFSHORE EASTERLY FLOW THROUGH MIDWEEK. WHILE WINDS ARE LARGELY
AT 10 KT OR LESS, AREAS DOWNWIND OF GAPS IN THE COASTAL TERRAIN
MAY SEE STRONGER FLOW WITH GUSTS UP TO 15-20 KT, MAINLY WEST OF
THE MOUTH OF THE COLUMBIA RIVER. SEAS REMAIN BELOW 10 FT AT 10-13
SECONDS THROUGH THE MIDDLE OF THE WEEK. -03/36
PQR WATCHES/WARNINGS/ADVISORIES
OR...AIR STAGNATION ADVISORY UNTIL 4 PM PST WEDNESDAY FOR ORZ109-
114>118.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page