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 00Z Thursday

Westerly flow aloft turns north- northeasterly tonight as an upper level trough drops southward over the Pacific Northwest. Predominately VFR conditions are expected to continue as mid to high level clouds drift across the airspace. Lower VFR to MVFR stratus is likely along the north Oregon coast through this afternoon with spotty rain showers possible. Chances for MVFR CIGs at coastal terminals remain around 20-30% through 23z today. Otherwise, expect light winds to become north to northwest around 4-8 kt through early this evening.

KPDX AND APPROACHES...VFR conditions expected through the TAF period, with mid to high level clouds through this evening. Northwest winds persist at around 3-7 kt. /DH

MARINE

North to northwest winds continue today 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. As a result, Small Craft Advisories have been issued for the coastal waters south of Cape Falcon from 2 to 11 PM Wednesday. Small Craft winds could hold on until 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. /DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 2 PM to 11 PM PDT Wednesday for PZZ252- 253-272-273.