textproduct: Portland

SYNOPSIS

Lingering showers across the area through Friday morning as weakening low pressure moves further inland. Dry weather returns this afternoon and persists through the weekend as high pressure builds over the Pacific Northwest. Expect near to slightly above normal temperatures and increased offshore flow this weekend. Another shortwave trough returns chances for showers on Monday, with another potential system mid-to-late next week.

DISCUSSION...Now through Thursday night

Radar imagery as of early Friday morning depicts scattered showers across northwest Oregon and southwest Washington as a weakening low pressure system progresses inland. Today (Friday), an upper level ridge builds over the Pacific Northwest, which will decrease shower activity throughout the day and return drier conditions. We should also see some cloud breaks by this afternoon/evening.

The ridge of high pressure amplifies and persists throughout the weekend, so expect dry weather and near-to-slightly above normal high temperatures through Sunday (upper 50s to low 60s). Also worth mentioning is that easterly winds will increase this weekend as offshore pressure gradients tighten. The breeziest easterly winds will be through the western Columbia River Gorge and Portland/Vancouver Metro Area, and Cascades. The latest model guidance suggests the surface pressure gradient from Troutdale (KTTD) to The Dalles (KDLS) will most likely peak around -6 mb Saturday night before easing to around -4 mb Sunday afternoon. This suggests peak wind gusts up to 30-40 mph in the far east Portland Metro area (Troutdale/Camas) and up to 50 mph for exposed ridgetops and our typically breeziest spots like Crown Point and Three Corner Rock.

Sunday night into Monday, the upper ridge will begin to flatten as a shortwave trough dips south into southwest British Columbia and far northwest Washington. Since most ensemble guidance suggest that this system will track further north of our area, precipitation amounts are not looking significant or impactful. The highest chances for rain are along the coast and southwest Washington (50-70%), while chances for rain are lower (20-40%) across interior northwest Oregon. Chances for 0.25" of rain or more in a 24 hr period from 4 AM Mon - 4 AM Tue are only 20-30% along the coast and 5-15% across the Willamette Valley and southwest Washington lowlands.

Another upper level ridge builds over the Pacific Northwest on Tuesday, bringing a brief return of dry weather. By Wednesday, this ridge quickly gets pushed eastward as the next frontal system approaches. The majority of ensemble members (70-80%) are in general agreement of light rain returning by Wednesday night and continuing into Thursday. Note that there is still some uncertainty with exact precipitation amounts. -10

AVIATION

Radar imagery and terminal observations as of early Friday morning depicts lingering showers and mid-to-high level cloud cover across northwest Oregon as a weakening low pressure system progresses inland. Not expecting fog tonight due to cloud cover and lack of calm winds. High pressure building over the Pacific Northwest on Friday will lead to decreasing showers and VFR conditions through the majority of the TAF period. Southerly to southwesterly winds around 5-8 kt this morning become variable under 5 kt in the afternoon as pressure gradients ease. After 00z Sat, guidance suggests increasing cloud breaks which persist into late Friday night. Late in the TAF period (06-12z Sat), moist low levels will support a 20-30% chance for IFR/MVFR low stratus development across the Willamette Valley.

KPDX AND APPROACHES...Predominately VFR with high clouds through the majority of the TAF period. Showers linger through Friday morning, then gradually dry up into the afternoon. Variable winds around 5 kt or less. 20-30% chance for IFR/MVFR CIGs between 06-12z Sat. -10

MARINE

Westerly winds will gradually ease Friday to around 5-10 kt as low pressure weakens. However, a strong westerly swell will maintain hazardous seas across the waters into Friday morning. The latest observations at buoy 46029 and 46050 as of early Friday morning show seas around 15-19 ft at 13-14 sec. These seas are forecast to hold through mid-morning Friday before gradually subsiding throughout the day. Therefore, went ahead and extended the Hazardous Seas Warning for all marine zones including the Columbia River Bar through 4 PM Friday.

Following the Hazardous Seas Warning, a Small Craft Advisory has been issued across all waters including the Columbia River Bar from 4 PM Friday to 7 AM Saturday for seas around 10-14 ft at 12-13 sec. High pressure builds heading into the weekend, maintaining relatively benign marine conditions with winds remaining under 15 kt. Winds do begin to turn more easterly on Saturday as an offshore pressure gradient develops. Minimal impacts expected as guidance suggests a less than 10% chance for frequent wind gusts greater than 21 kt and a >90% chance for seas under 10 ft this weekend. -10

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Hazardous Seas Warning until 4 PM PST this afternoon for PZZ210- 251>253-271>273.

Small Craft Advisory from 4 PM this afternoon to 7 AM PST Saturday for PZZ210-251>253-271>273.