Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
868 FXUS66 KPQR 271047 AFDPQR Area Forecast Discussion National Weather Service Portland OR 347 AM PDT Fri Sep 27 2024 .SYNOPSIS...Dry conditions and seasonable temps return today in the wake of a weak cold front. High pressure rebuilds into the region, bringing gusty northerly winds to the area this afternoon. Another seasonable day is expected on Saturday before a weak disturbance passes overhead Saturday night into Sunday. Below average temperatures are expected on Sunday but no precipitation. Return to warmer and drier weather early next week, but uncertainty remains in the forecast from Wednesday onward. && .SHORT TERM...Now through Sunday...Satellite and radar imagery depict widespread cloud cover across the area and light rain showers, mainly north of the Salem. The cold front supporting these conditions is associated with a low pressure system coming onshore along the central British Columbia and is located just off the WA and OR coasts. Light shower activity is expected to dissipate by 18Z this morning and should only result in light totals of a few hundredths at any given location. Expect dry weather today as high pressure re-builds. Surface high pressure offshore will maintain onshore flow, with winds shifting more northerly/northwesterly. Winds could get breezy with gusts up to 30 mph along the coast and 20-25 mph in the central/southern Willamette Valley. Temperatures will be seasonable with highs in the low to mid 70s for interior valleys and 60s along the coast. Friday night, models are indicating a weak thermal trough developing over the Willamette Valley. This will lead to light easterly winds over the Cascades, however winds are not expected to be very gusty/impactful as KTTD-KDLS pressure gradients are forecast between -2 to -3 mb. Easterly wind gusts are forecast around 10-15 mph, strongest along the Cascade crest. Saturday morning, light easterly winds will continue but the thermal trough is forecast to break down by late morning. This will return onshore flow to the Cascades and breezy west winds through the Columbia River Gorge with gusts to 25-30 mph. Expect another with seasonable highs similar to Friday. A weak short wave trough is expected to move overhead Saturday night into Sunday which will bring slightly below average temperatures to the area on Sunday. Highs are expected to top out in the upper 60s inland and upper 50s to low 60s for the coast. Precipitation is not expected with this wave as the upper levels remain dry. -Batz .LONG TERM...Sunday night through Thursday...The majority of members from the WPC cluster analyses (60%+) depict upper level ridging returning to the Pacific Northwest early next week. 500 mb heights will be above-average, so this scenario would likely re-bound temperatures into the low to mid 70s for interior valleys and mid to upper 60s along the coast. Will note that models are indicating the potential for a thermal trough developing again over the Willamette Valley, which would lead to increased offshore flow over the Cascades Sunday night through Monday. Forecast relative humidities will fall near critical thresholds (25%) in the Cascades Mon/Tue, however, recent rainfall/moisture will help make vegetation less susceptible to burning. Confidence wanes into the middle of next week as half of the members depict continued ridging and the other half begin to show troughing returning to the area. The NBM temperature spread between the 25th and 75th percentile also begin to widen by 10 to 15 degrees. We`ll see how the long term forecast shapes up over the following days. If we maintain ridging then expect warmer and drier weather, and if we return to troughing then expect cooler and potentially wetter weather. -Batz/Alviz && .AVIATION...A weak front continues to push through the coast and inland, bringing spotty showers into this morning. MVFR CIGS will continue along the coast, with intermittent IFR conditions (20-30% chance) until 17-19Z Friday. Inland, high-end MVFR CIGS between 2-3 kft will linger until 17-19Z Friday. Thereafter, clouds will gradually break up and maintain widespread VFR conditions through the rest of the TAF period. Winds will gust up to 25-30kt along the coast and up to 15 kt inland between 18Z Friday to 03Z Saturday. PDX APPROACHES...MVFR CIGs and showers will continue until 17Z Friday. NW winds pick up to around 10 kt by 22-23Z Friday. ~Hall && .MARINE...Robust low pressure nears British Columbia this morning. Trailing cold front continues to push through the waters and onshore, bringing gusty south winds to the waters. South winds will gust 20 to 30 kt and combined seas at 8 to 12 ft, therefore will maintain the Small Craft Advisory for all outer and coastal waters. High pressure builds over the offshore waters behind the front. As such, will see a return of northerly winds this afternoon, along with tightened pressure gradients bringing 20 to 25 kt wind gusts from Cascade Head southward. These winds will continue through Saturday. As often is the case, winds will ease a bit during the overnight and early daytime hours. The fetch of west to northwest swell from the storm over the Gulf of Alaska will persist this morning into Saturday, with swell building to 10 to 13 ft. Along with wind chop, expect overall seas up 12 to 15 ft, with highest seas farther offshore. While the swell will decrease tonight, gusty north winds will continued keep seas somewhat choppy at 6 to 8 ft into Saturday. Winds/seas decrease Sunday, running at 10 to 15 kt with seas 3 to 6 ft for early next week. ~Hall/Rockey && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 5 PM PDT this afternoon for PZZ210. Small Craft Advisory until 2 PM PDT Saturday for PZZ251-271- 272. Small Craft Advisory until 2 PM PDT Saturday for PZZ252-253- 273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland