390
FXUS66 KPQR 302210
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
210 PM PST TUE DEC 30 2025
SYNOPSIS
HIGH PRESSURE REMAINS ANCHORED OVER THE REGION
THROUGH WEDNESDAY. COOL AND DRY CONDITIONS LEAD A FAVORABLE
ENVIRONMENT FOR FROST AND FOG DEVELOPMENT DURING THE OVERNIGHT
AND MORNING HOURS THROUGH THURSDAY MORNING. A PATTERN SHIFT IS
IN STORE BEGINNING THURSDAY WITH RELATIVELY WARMER AIR AND
PRECIPITATION RETURNING, CONTINUING INTO EARLY NEXT WEEK.
DISCUSSION...TUESDAY AFTERNOON THROUGH MONDAY
VISIBLE
SATELLITE IMAGERY TUESDAY AFTERNOON DEPICTS MOSTLY CLEAR SKIES
ACROSS NW OREGON AND SW WASHINGTON EXCEPT FOR A FEW LINGERING
AREAS OF STRATUS IN INTERIOR VALLEYS. UPPER LEVEL HIGH PRESSURE
REMAINS OVER THE REGION TODAY WITH THE AXIS OVER WESTERN OR/WA,
AND A THERMALLY INDUCED TROUGH REMAINS AT THE SURFACE. THIS HAS
CAUSED A TIGHTENING OF PRESSURE GRADIENTS OVER THE CASCADES,
LEADING TO GUSTY EAST WINDS THROUGH CASCADE VALLEYS, ESPECIALLY
THE WESTERN COLUMBIA RIVER GORGE. GUSTS UP TO 25-35 MPH ARE
EXPECTED IN THE WESTERN PORTLAND METRO AREA WITH UP TO 35-45 MPH
POSSIBLE AROUND TROUTDALE THROUGH THIS AFTERNOON. LOCAL GUSTS
UP TO 50-55 MPH HAVE BEEN OBSERVED AT THE TYPICAL WINDIEST
LOCATIONS SUCH AS CORBETT, CROWN POINT, AND THREE CORNER ROCK.
THE UPPER LEVEL RIDGE AXIS BEGINS MOVING EAST OF THE CASCADES
LATER THIS AFTERNOON AND THROUGH WEDNESDAY, ALLOWING THE THERMAL
TROUGH AND SUBSEQUENT SURFACE PRESSURE GRADIENTS TO WEAKEN.
BREEZY EAST WINDS WILL SUBSIDE SLIGHTLY THIS EVENING, THOUGH
GUSTS UP TO 35-40 MPH ARE STILL POSSIBLE EAST OF TROUTDALE.
WINDS CONTINUE SUBSIDING THROUGH THE DAY WEDNESDAY.
COLD TEMPERATURES ARE EXPECTED AGAIN TONIGHT INTO WEDNESDAY
MORNING AND AGAIN WEDNESDAY NIGHT INTO THURSDAY MORNING DUE TO
MOSTLY CLEAR SKIES WITH TEMPERATURES IN THE UPPER 20S TO LOW 30S
ACROSS INLAND VALLEYS, MID TO UPPER 30S ALONG THE COAST, AND
LOW 20S TO LOW 30S IN THE CASCADES. COLDEST TEMPERATURES WILL BE
TONIGHT INTO WEDNESDAY MORNING. ADDITIONALLY, FOG AND LOW
STRATUS ONCE AGAIN HAVE THE POTENTIAL TO FORM DURING THE SAME
TIME PERIODS, MAINLY ALONG THE I-5 CORRIDOR FROM THE SOUTHERN
WILLAMETTE VALLEY NORTH THROUGH COWLITZ COUNTY. BOTH FOG AND
FROST ARE LESS LIKELY IN THE PORTLAND METRO AREA, ESPECIALLY ON
THE EAST SIDE, DUE TO THE INCREASED EAST WINDS FROM THE GORGE.
ANOTHER AREA OF CONCERN IS STAGNANT AIR UNDER THIS RIDGING. A
STRONG INVERSION REMAINS IN PLACE THROUGH WEDNESDAY AFTERNOON
WITH STABLE AIR IN PLACE NEAR THE SURFACE. THIS WILL ALLOW FOR
AN INCREASE IN AIR QUALITY CONCERNS, ESPECIALLY FOR LOCATIONS
OUTSIDE OF THE WINDIER EASTERN PORTLAND METRO AREA. IF YOU ARE
SUSCEPTIBLE TO AIR QUALITY CONCERNS, BE SURE TO MONITOR AIR
QUALITY THROUGH AIR NOW.
A PATTERN CHANGE IS ON THE WAY FOR THURSDAY, WITH WET CONDITIONS
RETURNING AND CONTINUING INTO EARLY NEXT WEEK. ENSEMBLE
GUIDANCE INDICATES A LONGWAVE TROUGH DEEPENING OVER THE EASTERN
PACIFIC ON THURSDAY AS A SEPARATE CLOSED LOW APPROACHES
CENTRAL/SOUTHERN CALIFORNIA FROM THE WEST. SOME UNCERTAINTY
REMAINS IN THE SPECIFICS OF THE PATTERN ON THURSDAY INTO
SATURDAY, BUT THE GENERAL CONSENSUS AMONGST THE GFS, EURO, AND
CANADIAN ENSEMBLES IS ON THURSDAY, THE LOW APPROACHING
CALIFORNIA WILL CONTINUE MOVING EAST WITH A SECONDARY WEAK
SHORTWAVE MOVING NORTH ALONG THE MAIN LONGWAVE TROUGH INTO THE
PACNW. THIS SHORTWAVE WILL CARRY ENOUGH MOISTURE FROM THE CLOSED
LOW TO BRING PRECIPITATION CHANCES SPREADING NORTH INTO NW
OREGON AND SW WASHINGTON SOMETIME ON THURSDAY, THOUGH
UNCERTAINTY REMAINS ON WHETHER THE RAIN WILL START EARLIER IN
THE DAY ON THURSDAY OR LATE THURSDAY NIGHT INTO FRIDAY MORNING.
THEN THE LONGWAVE TROUGH SLOWLY MOVES EAST THROUGH THE EASTERN
PACIFIC ON FRIDAY INTO SATURDAY, WITH RAIN CONTINUING IN THE
REGION. ADDITIONALLY, WARMER AIR WILL ACCOMPANY THE RAIN
BEGINNING THURSDAY WITH 850 MB TEMPERATURES REMAINING ABOVE 0
DEG C THROUGH SATURDAY, AND SNOW LEVELS WILL RISE TO ABOVE
4500-5500 FEET, MEANING SNOW IS ONLY LIKELY OVER THE HIGH
CASCADES. ENSEMBLES INDICATE A FRONTAL SYSTEM WILL MOVE INLAND
FROM THE WEST SOMETIME ON SATURDAY ACCOMPANIED BY A STRONGER
WAVE ALONG THE LONGWAVE TROUGH. THIS COULD BRING A PERIOD OF
BREEZY WINDS ALONG THE FRONTAL PASSAGE, BUT STRONG WINDS ARE NOT
EXPECTED. NBM INDICATES AROUND A 50% CHANCE ALONG THE COAST OF
GUSTS ABOVE 40 MPH WITH A 10-25% CHANCE FOR INLAND AREAS.
THE SPECIFICS OF THE WEATHER PATTERN BECOME MUCH MORE UNCERTAIN
IN ENSEMBLE GUIDANCE SUNDAY INTO MONDAY, BUT IN GENERAL, UPPER
LEVEL TROUGHING REMAINS, BRINGING CONTINUED RAINY CONDITIONS.
NONE OF THE RAIN THURSDAY INTO MONDAY IS EXPECTED TO BE
IMPACTFUL OR CAUSE FLOODING CONCERNS AND INSTEAD WILL BE MORE OF
A TYPICAL WINTER RAIN FOR THE PACNW. LOOKING AT NBM'S POTENTIAL
72 HOUR RAIN TOTALS FROM 4 AM FRIDAY THROUGH 4 AM MONDAY, THE
MEAN SCENARIO (OR MOST LIKELY SCENARIO) SUGGESTS AROUND 0.75-1
INCH FOR INTERIOR LOWLANDS AND 0.75-2 INCHES FOR THE COAST AND
CASCADES. THE HIGH END SCENARIO (10% CHANCE OF EXCEEDING THESE
VALUES) INDICATES AROUND 1.25-1.75 INCHES FOR THE INTERIOR
LOWLANDS, 1.3-3 INCHES FOR THE CASCADES, AND 2-4 INCHES FOR THE
COAST. FOR THE LOW END SCENARIO (90% CHANCE OF EXCEEDING THESE
VALUES), NBM INDICATES 0.25-0.4 INCHES FOR THE INTERIOR
LOWLANDS AND 0.4-0.9 INCHES FOR THE CASCADES AND COAST. -03
AVIATION
AN UPPER LEVEL RIDGE OF HIGH PRESSURE OVER THE REGION
WILL MAINTAIN PREDOMINATELY VFR CONDITIONS THROUGH THE PERIOD. A
FEW AREAS OF LOW STRATUS REMAIN IN FAR SOUTHEAST PARTS OF THE
SOUTHERN WILLAMETTE VALLEY AS WELL AS ALONG THE LOWER COLUMBIA
RIVER NEAR KKLS WHERE A SURFACE INVERSION IS KEEPING THE COLDER
AIR, ALONG WITH SOME NEAR SURFACE MOISTURE, TRAPPED. A STRONG
OFFSHORE PRESSURE GRADIENT WILL MAINTAIN BREEZY EAST WINDS THROUGH
THE COLUMBIA RIVER GORGE RESULTING IN GUSTS UP TO 30-35 KT AT
KTTD. GIVEN THE PERSISTENT, STRONG EASTERLY FLOW, THERE IS THE
POTENTIAL FOR LLWS FOR KPDX AND KHIO THROUGH THE TAF PERIOD AS
WELL.
TEMPERATURES AGAIN FALL INTO THE UPPER 20S TO LOWER 30S ACROSS
THE WILLAMETTE VALLEY TONIGHT, RESULTING IN WIDESPREAD AREAS OF
FROST, WITH LOWER CONFIDENCE OF PATCHY DENSE FOG DEVELOPING.
HIGHEST CHANCES FOR FOG AND FREEZING FOG DEVELOPMENT WILL AGAIN
BE IN THE SOUTHERN WILLAMETTE VALLEY, INCLUDING KEUG.
KPDX AND APPROACHES...VFR CONDITIONS EXPECTED TO PERSIST THROUGH
THE TAF PERIOD. EASTERLY WINDS AROUND 8-12 KT EXPECTED THROUGH
THIS EVENING. STRONG EAST WINDS FROM THE COLUMBIA RIVER GORGE ARE
NOT EXPECTED TO IMPACT THE TERMINAL DIRECTLY. HOWEVER, GIVEN THE
PERSISTENT STRONG, EASTERLY FLOW, THERE IS THE POTENTIAL FOR LLWS
THROUGH TONIGHT. /DH
MARINE
HIGH PRESSURE REMAINS OVER THE REGION THROUGH THE MIDDLE
OF THE WEEK. STRONGER HIGH PRESSURE INLAND WILL MAINTAIN OFFSHORE
WINDS ACROSS THE COASTAL WATERS THROUGH TONIGHT, BEFORE BECOMING
MORE SOUTHERLY ON WEDNESDAY. WINDS EXPECTED TO REMAIN AROUND 10
KT OR LESS, WHILE SEAS PERSIST AROUND 6 TO 7 FT THROUGH WED NIGHT.
SOUTHEASTERLY WINDS INCREASE ON THURSDAY TO AROUND 15 KT AS A LOW
PRESSURE SYSTEM BEGINS TO DEVELOP WELL OFFSHORE FROM THE NORTHERN
CALIFORNIA COAST. THIS LOW PRESSURE SYSTEM IS EXPECTED TO
STRENGTHEN OFFSHORE LATE IN THE WEEK, ALTHOUGH THERE REMAINS
CONSIDERABLE UNCERTAINTY REGARDING THE STRENGTH AND POSITION OF
THE LOW INTO THE WEEKEND. THAT SAID, THERE IS AROUND A 60-70%
CHANCE OF GALE FORCE WIND GUSTS OCCURRING ACROSS THE WATERS
SOMETIME LATE FRIDAY INTO SATURDAY. THESE STRONGER WINDS, COMBINED
WITH A DEVELOPING FRESH SOUTHERLY SWELL WILL LIKELY PUSH SEAS INTO
THE LOWER TO MID TEENS BY SATURDAY, WITH A 10-15% CHANCE OF
EXCEEDING 20 FT. /DH
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
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