textproduct: Portland

SYNOPSIS

A weak trough will continue to bring scattered clouds and cool weather this afternoon. Warmer and drier conditions return Wednesday and Thursday as easterly winds develop across the Columbia Gorge, Cascades, and Coast Range with northerly winds along the I-5 corridor. Winds from the west return Thursday afternoon. Dry and warm conditions continue Friday through the weekend, with potential for cooler weather next week.

SHORT TERM...Today through Thursday night

Satellite imagery as of early Tuesday afternoon depicts widespread high-level clouds across northwest Oregon and southwest Washington as a weak upper-level trough swings through the region. Radar imagery is also showing some scattered light showers, however, surface observations have shown no measurable precipitation so far. In addition, model soundings are showing a drier low-level atmosphere, which suggests that these showers could be falling as virga. Therefore, hourly chances for precipitation for the rest of the day remain below 10% for most locations except 20-40% along the crest of the Cascades. Expect high temperatures this afternoon to peak in the upper 60s across interior valleys and low to mid 60s along the coast due to the cloud cover.

The aforementioned trough will shift southward into northern California tonight into Wednesday and turn into a closed low as upper-level ridging strengthens offshore. Thermal troughs will develop along the coast and Cascade foothills, supporting a return of winds from the east/northeast through the Columbia River Gorge and downsloping off the Cascades and Coast Range. These downsloping winds will support drier and warmer air along the coast and I-5 corridor, with high temperatures rebounding into the upper 70s to low 80s across interior valleys and low 70s along the coast.

Ensemble guidance continues to suggest pressure gradients between KTTD and KDLS are expected to fall into the -1 to -3 mb range, supporting gusts around 20-30 mph through the Gorge and east-west aligned gaps through the Cascades, with locally breezier gusts up to 40 mph for exposed ridgetops. There is only a 5-15% chance for wind gusts exceeding 40 mph for these ridgetops. Meanwhile, the central and southern Willamette Valley will also become breezy as winds turn more northerly into the I-5 corridor. Wind gusts across the Valley are expected to peak around 20-25 mph, with a 10% chance for gusts exceeding 30 mph. While these easterly winds. Despite the warmer temperatures and increasing easterly winds, afternoon humidity should remain above 30% due to recent moisture, keeping concerns for rapid fire spread minimal.

Thursday remains the warmest day of the week. Weak offshore flow will continue through the morning, with high confidence for interior valley highs peaking in the low 80s. Thermal troughing should break down Thursday afternoon, allowing onshore flow to return. Meanwhile, the upper-level low over northern California will shift northeastward toward the Great Basin. Some wrap- around moisture could produce a 5-10% chance of thunderstorms along the crest of the Lane County Cascades Thursday, while the remainder of the forecast area remains dry and outside the thunderstorm threat. SPC has included a portion of the Lane County Cascades in a general thunderstorm risk, so this potential will need to be monitored as Thursday approaches. -10/12

LONG TERM...Friday through Monday

The forecast becomes more uncertain Friday through the weekend as ensemble guidance diverges on how quickly the upper-level pattern evolves. Roughly half of the guidance maintains weak troughing over the Great Basin, which would keep temperatures closer to the low 70s, while the other half favors stronger ridging over the Pacific Northwest and warmer temperatures potentially reaching the mid 80s. Thus, there is still a fairly broad range in possible temperatures late in the week, but the overall signal continues to favor dry weather. By early next week (Monday), most ensemble members begin to hint at an upper- level trough dropping down from the Gulf of Alaska. The impacts of this trough remain uncertain for the Pacific Northwest at this time, but it would suggest a continuation of onshore flow and potentially cooler temperatures next week. -10/12

AVIATION...Through 06Z Thursday

At 0515Z Wednesday, VFR flight conditions were being observed at all TAF sites under mostly clear skies. A few clouds remain around 6000 ft, however these clouds are expected to dissipate later tonight. Expect mostly clear skies thereafter for the remainder of the 06Z TAF period, resulting in continued VFR conditions.

Offshore winds begin to develop at the surface beginning early Wednesday morning. By Wednesday afternoon, east to northeast winds will increase at KTTD, KUAO, KHIO, and KPDX with gusts as high as 20 kt. North winds will increase from KSLE to KEUG and at KONP Wednesday afternoon with gusts as high as 25 kt. North winds will be weakest at KAST. It appears winds will weaken in strength by 03Z Thursday.

KPDX AND APPROACHES...VFR conditions expected through the TAF period with mostly clear skies. Northwest winds around 6-7 kt this evening will become northerly around 10 kt by 18Z Wednesday. By approximately 20-21Z Wednesday, winds should become northeasterly with wind gusts up to 20 kt. The exact timing winds will transition from northerly to northeasterly is unclear, and may occur anytime between 18-22Z Wednesday. Winds should weaken fairly quickly between 02-03Z Thursday. -23

MARINE

North winds will continue tonight as high pressure builds offshore. A strengthening thermal trough along the coast is expected to increase pressure gradients across the coastal waters on Wednesday, increasing northerlies to 15-20 kt with gusts up to 25 kt south of Cape Falcon. Isolated gusts as high as 30 kt are possible over the southern outer waters to the south of Cape Foulweather, beyond 10 NM offshore. Gusts are now expected to approach 20-25 kt by late Wednesday morning for the central and southern offshore waters, and by Noon over the inner waters. As a result, Small Craft Advisories have been extended in time to begin at 11 AM Wednesday and end at 11 PM Wednesday. Small Craft winds could hold on until as late as 2 AM Thursday but confidence remains low at this time.

Winds are likely to ease later in the week as low pressure drifts offshore. A persistent northwest swell around 4 to 5 ft at 7 to 8 seconds is expected to continue through tonight. Seas then build to around 6 ft on Wednesday as northerly winds strengthen. Northerlies strengthen again over the weekend, with around a 40-50% chance of wind gusts exceeding 21 kt. -23/DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 11 AM to 11 PM PDT Wednesday for PZZ252-253-272-273.