Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
903 FXUS66 KPQR 230144 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 644 PM PDT Sat Jun 22 2024 .SYNOPSIS...Cooler temperatures will return Sunday into Monday as onshore flow strengthens, along with some light rain/aggressive drizzle tonight into Sunday morning for the Coast Range and Cascades. Warm and dry conditions return Tuesday. Precip chances become more widespread Wednesday into Thursday as a more robust upper level trough moves inland, which will also bring the return of cooler temperatures. && .SHORT TERM...Now through Tuesday Night...The upper level ridge which has been the dominant synoptic feature the past few days, will continue to break down tonight as the a broad upper level trough from Hadia Gwaii pushes eastward through Sunday. High resolution models are showing a cold front that is associated with the upper level trough will bring near normal daytime high temperatures to the region on Sunday. Daytime highs in the upper 60s to low 70s for inland locations, upper 50s to mid 60s for the Cascades and low to mid 60s for the coast. In addition to the cooler temperatures, areas along the Coast, Coast Range and Cascades could see some very light rain/aggressive drizzle starting later tonight and continuing through Sunday afternoon. While the cooler temps and moister conditions may be welcomed, do not expect any amount of significant rainfall accumulation with this front. In fact, most locations will likely not see any precipitation. After this broad trough has pushed eastward late Sunday, the region develops a zonal flow pattern, which will signal the start of another warming trend for the middle part of the week. Currently, daytime highs are expect to warm into the mid to mid 70s inland, upper 60s to low 70s for the Cascades and upper 50s to mid 60s along the coast. Tuesday, the warming trend will continue as a Great Basin high will stretch northward, resulting in 850 mb temperatures reaching toward 11C to 15C which means that daytime highs will likely warm once again. Overall, expect warm and dry conditions to persist through the middle of the upcoming week. -42 .LONG TERM...Wednesday through Saturday...Wednesday continues to see the trailing end of the ridge as it moves out, with a 75% chance of temperatures above 75 degrees. The next shortwave begins to move in late Wednesday which could bring some light rain as the next shortwave trough begins to move in. There is around a 20% chance of 24hr rainfall (Wed 5am - Thu 5am) above 0.10" at the WA coast, WA Coast Range, and WA Cascades. At inland/lowland areas, chance is lower than 5%. WPC Cluster analysis shows an 85% chance of a shortwave trough fully moving in on Thursday, with slightly stronger rain accumulations expected, as well as cooler temperatures. Temperatures will be in the low 70s, with only a 25% chance of temperatures over 75 degrees. Precipitation is skewing weaker than previous forecasts, with around a 30-40% chance of 24hr accumulation (Thu 5am - Fri 5am) at the coast, Coast Range, and Cascades above 0.10". This drops to 10% in the Willamette Valley, under 5% south of Salem. Friday is expected to see similar conditions, and Saturday sees 70% ensemble agreement in a return to zonal flow, with possibly some insubstantial drizzle.-JLiu && .AVIATION...Skies cleared more than expected along the coast today, and as of 2130z skies along the coast were mostly clear KTMK southward. North of KTMK, clouds are increasing with VFR cigs generally between 040-050. A weak cold front will cause clouds to continue to thicken and spread southward along the coast this afternoon and evening, with hi-res probabilistic guidance suggesting over an 80% chance of MVFR cigs for the entire S WA/N OR coast by 23/02z. Areas of coastal drizzle will likely push cigs/vsbys into the IFR category for some coastal locations between 23/00z-06z. The cold front will also lead to a strong onshore push this evening with gusts 20-25 kt likely through gaps in the Coast Range. Eventually this will cause stratus to develop along the Cascade foothills then backbuild into the Willamette Valley, with increasing chances of MVFR later in the evening. By 08z, latest high-res forecast models suggest greater than a 70-80% chance of MVFR cigs for the Willamette Valley terminals east of I-5 (i.e KPDX, KTTD, KSLE, KUAO, etc). Suspect this is about accurate for cigs in general, but cig heights may end up just above 030 for some of this area. With onshore flow persisting into Sunday and the moist layer considerably deeper than today, clouds should linger well into the day. Isolated showers are not out of the question over the Coast Range and Cascades Sunday. -Weagle PDX AND APPROACHES...VFR with mainly clear skies and light onshore flow today. W-NW winds will increase considerably after 22/23z-24z, with sustained winds 10-15 kt and gusts up to 25 kt between 23/00z-08z. Winds will gradually decrease thereafter. Backbuilding stratus from the Cascade foothills will lead to a 70-80% chance of cigs by 23/10z, but chances of MVFR are closer to 50%. Cigs that develop will persist well into the day Sunday.-Weagle && .MARINE... Low pressure near 1000 mb was approaching Haida Gwaii Sat morning, pushing a weak cold front across the Pac NW coastal waters later today. Trajectory of low pressure does suggest a weak dynamic fetch which could push seas up close to 10 ft Sunday afternoon and evening. That said, the odds of seas reaching 10 ft are too low (20-30%) to warrant a Small Craft Advisory at this time. Otherwise, high pressure will expand across the waters Sunday and Monday while thermal low pressure strengthens over the Sacramento Valley and near the OR/CA border. This will lead to moderate N-NW flow early next week, with about a 30-40% chance of wind gusts exceeding SCA criteria of 21 kt Monday afternoon. -Weagle && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland