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Seaside, Oregon Weather Forecast Discussion

830
FXUS66 KPQR 112219
AFDPQR

Area Forecast Discussion National Weather Service Portland OR 319 PM PDT Thu Sep 11 2025

.SYNOPSIS...Expect a gradual transition to warmer conditions and sunnier skies through the first half of the weekend. Then, our next frontal system arrives later Saturday night to Sunday ushering in a period of widespread light rain. Conditions dry and warm up again early next week with the potential for offshore winds on Tuesday.

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.SHORT TERM...Now through Saturday Night...This afternoon Satellite imagery shows widespread stratus just beginning to break up across the Willamette valley as westerly flow and deep marine influence dominate the pattern near the surface. Aloft, the upper-level low which has facilitated several rounds of showers and thunderstorms over the region the the last several days has finally progressed into northern Nevada keeping the coverage of any activity fairly limited to the Oregon Casacdes into the evening hours before dry weather returns. While the storm motion will have a slight easterly component (NNE to SSW), the aforementioned marine layer just west of the crests will ensure storms weaken and decay if/when they shift off the crests.

Starting tomorrow (Friday) a transient shortwave ridge which as been holding over the eastern Pacific begins to shift overhead leading to a thinner deck of morning low clouds inland and generally sunnier skies by the afternoon hours. Due to the more expedient clearing, highs likely jump into the mid 70s around the Portland/Vancouver metro and mid to upper 70s central and south Willamette Valley. The axis of the high pressure ridge passes overhead on Saturday which will almost certainly end up a the warmest day of the next ~4-5 days or so - temperatures peak in the upper 70s to low 80s Willamette Valley and Cascade Valleys. However, Saturday evening clouds begin to increase from the west thanks to an approaching frontal boundary slated to bring at least light widespread rainfall to the region for the latter half of the weekend. -Schuldt

.LONG TERM...Sunday through Thursday...Widespread rain returns across northwest Oregon and southwest Washington as our first fall-like frontal system swings through the region. Ensemble guidance systems(ENS/GEFS/GEPS) are in general agreement (80% chance) that the front will move through late Saturday night into Sunday morning, which is when the bulk of the rain is expected. The latest 12 NAM still appears to be an outlier pushing the bulk of the energy with this front further south into southern Oregon and northern California. If this scenario were to occur, then we would end up much drier than forecasted.

While the ensemble models are in general agreement with the timing of the front, there is still uncertainty with the magnitude of the front, and thus total rainfall amounts. The NBM 75th percentile for 24 hour rainfall ending 5 PM Sunday is around 1.2-1.5" along the coast and 0.50-0.80" across interior valleys, while the NBM 25th percentile is around 0.30-0.50" along the coast and 0.05-0.20" across interior valleys. Currently, the GEFS ensemble is wanting to bring in the higher- end rainfall amounts while the ENS/GEPS ensembles are suggesting lower amounts. Will continue to monitor how this evolves in the next day or so. For now, we can generally say that Sunday is looking to be wetter and cooler. By late Sunday afternoon, the front will weaken and rain will gradually taper off Sunday night into early Monday morning.

The second half of Monday looks drier as shortwave ridging returns in earnest and the aforementioned system progresses eastward. By Tuesday, there is high agreement among ensemble members that above- average 500 mb heights return, rebounding temperatures into the low 80s across interior valleys with sunny skies. Wednesday looks similar to Tuesday, however, a decent subset of ensemble members (~40%) do also show a weak front approaching the Pacific Northwest.

It`s worth highlighting late Monday night through Tuesday into Wednesday a thermal trough develops across western Oregon with high pressure east of the Cascades, leading to an offshore flow pattern. There remains some uncertainty in the exact placement of this feature which will help to modulate the strength of offshore winds but for now they don`t appear particularly strong. This will be a period to monitor in the coming days. -Schuldt/Alviz

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.AVIATION...Predominately MVFR conditions persist across the area with minimal dissipation indicated on satellite. Expecting MVFR CIGs to persist across much of the area as guidance poorly handles the marine layer, though a brief break in the clouds is possible around 23z Thu to 02z Fri. Model soundings are indicating this cloud layer persisting through the night over the metro and northern Willamette valley. If stratus does dissipate inland, expect it to redevelop between 10-12z Fri. Winds remain light and variable, generally less than 10 kts.

There remains a 10-20% chance for a stray shower over the Cascades and Cascade Foothills through 06z Fri.

KPDX AND APPROACHES...MVFR conditions holding steady but the cloud deck seems to be rising slowly. A brief break in the clouds remains possible late this evening. If stratus does dissipate, it is expected to redevelop around 10-12z Fri. West to northwesterly winds less than 10 kts. -Batz

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.MARINE...High pressure remains in place over the waters through Friday morning. Winds out of the northwest at 10 kts or less and wind gusts below 15 kt. Winds become more variable during the latter half of Friday as a cold front begins to move closer to the region. Seas 5-6 ft at 12-14 seconds through Friday.

An approaching low pressure system will bring the aforementioned cold front toward the PacNW coast, shifting winds from northwesterly to southerly on Saturday. Probabilities for wind gusts of 21 kt or greater (small craft advisory criteria) are 50-70% when looking at 24 hour periods for Saturday and Sunday. However, when looking closer at the hourly probabilities, chances drop significantly to 10-30% at the highest on either day. This indicates that small craft gusts are definitely possible but likely won`t be widespread or long duration. Still something to watch in case the track of the low changes and confidence increases which would warrant a short small craft advisory. Seas are forecast around 6-7 feet at 10-12 sec through Saturday. A northwest swell is expected to move into the waters on Sunday bringing waves of 8-10 feet at 10-12 seconds which would support steep, hazardous seas for some time. -Batz

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.PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. &&

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NWS PQR Office Area Forecast Discussion

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