Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
912 FXUS66 KPQR 121823 AFDPQR Area Forecast Discussion National Weather Service Portland OR 1123 AM PDT Wed Aug 12 2026 Updated aviation discussion. && .SYNOPSIS...Warm and dry conditions expected through the weekend with persistent onshore flow. A stronger onshore push will bring increasing clouds and cooler temperatures today. Mostly dry through the weekend, with a chance of thunderstorms or showers over the Cascade crest Saturday afternoon. There are low chances for more widespread rain returning early next week, but significant rain does not appear likely. && .DISCUSSION...Today through Tuesday...Water vapor satellite imagery shows an upper level trough dropping out of British Columbia into the Pacific NW. This trough will allow for marine stratus to spread inland across much of SW Washington and NW Oregon with clouds lingering into the morning and early afternoon. Slightly cooler conditions are expected today with highs ranging from the mid-70s to lower 80s, while the coast likely remains in the 60s. Would not be surprised for some drizzle at the coast this morning as the marine layer deepens. Most of the moisture associated with the aforementioned trough is expected to remain across portions of the northern half of Washington, keeping us dry. There is agreement among the models and their ensembles for later in the week with the upper level pattern trending toward broad upper level troughing and a continuation of onshore flow. One nuance in the mid-levels on Thursday will be some light easterly winds in the 850-700 mb levels of the atmosphere, including near the Grasshopper Fire. This could cause some wildfire smoke to drift across portions of the area, mainly causing hazy skies by Thu afternoon. The potential range of afternoon high temperatures from the NBM for Thursday through Friday has generally consolidated into the lower to mid-80s, favoring near to slightly above average conditions for mid-August. Some uncertainty into the weekend, but ensembles are suggesting weak upper level ridging may nudge back into the Pacific NW as low pressure deepens the upper trough offshore. The latest cluster analysis shows more consistency between the models of low pressure dropping south off the central CA coast. This could result in a slight warming trend, though models suggest there is only a 10-20% chance of exceeding 90 degrees across the Willamette Valley on Sunday and Monday. Shortwave troughs within the more southwesterly flow aloft along with some increasing monsoonal moisture will also bring slight chances (10-20%) for thunderstorms along the Cascade crests of Oregon for Saturday afternoon, with the highest chances across the Lane County Cascades. The question then turns to the possibility of rain early next week, but chances for measurable precipitation remains low (15-30%) across the area next Monday and Tuesday. Cluster analysis of 500 mb heights shows a wide range of the magnitudes and placements of the upper level trough offshore, while only 10-15% of ensembles show the potential for any substantial rainfall (24 hour totals of > 0.25") across the area. DH/10 && .AVIATION...Through 18Z Thu...Westerly flow aloft continues as an upper level trough moves over the region. Marine stratus made a push inland this morning, butting up against the Cascade foothills. MVFR conditions continue at inland terminals and should improve to VFR by 19-21z Wed. MVFR to IFR conditions are being observed along the coast. Lowered flight conditions are expected to persist through the TAF period along the coast with around a 50% chance of brief improvement to VFR/high MVFR in the afternoon hours between 20z Wed through 00z Thu. Then there`s a 60-80% chance that IFR/LIFR conditions return along the coast between 02-06z Thu. The marine push will be less strong tonight into Thursday morning, so chances of marine stratus pushing inland during this time is lower with a 25-40% chance of MVFR ceilings at any hour between 10-16z Thu. Any lowered ceilings that do form should improve by 18-21z Thu. North to northwest winds are expected to increase to around 8-10 kt this afternoon, decreasing by 04-08z Thu. KPDX AND APPROACHES...Expect MVFR CIGs to persist through 19-21z Wed, improving to VFR after. Lingering afternoon clouds are expected to gradually lift and scatter out, with predominately VFR conditions likely through the rest of the TAF period. However, there is a 25-40% chance of MVFR CIGS developing again between 10-14z Thu. If these formed, expect improve to VFR conditions again by 18-20z Thu. Northwest winds around 5 kt are expected to increase to 8-10 kt after 23z Wed, decreasing after 06-08z Thu. -03 && .MARINE... No significant changes as high pressure offshore will continue to support northerly winds and fairly benign conditions across the coastal waters through the week and into the weekend. Winds from the north to northwest with gusts less than 21 kts will continue through at least the end of the week. Wind driven seas are expected to remain around 3 to 6 ft through the week. /DH && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland