Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
954 FXUS66 KPQR 182218 AFDPQR Area Forecast Discussion National Weather Service Portland OR 318 PM PDT Tue Jun 18 2024 .SYNOPSIS...Much drier and warmer through the remainder of the week with building high pressure. High probability of temperatures into the 90s inland. Even with the high temperatures, water remains cold. Cooler and wetter pattern approaching on Sunday, with increasing chances for precipitation late next week. && .SHORT TERM...Now through Friday...Satellite shows some spotty cumulus forming offshore and along the Cascades today due to northwesterly flow. Winds remain elevated along the coast, and the southern Willamette Valley in areas most susceptible to these north-northwesterly winds. Will see those winds ease overnight and become weakly offshore. With the clear skies, there is a slight chance for some lower patchy stratus and fog formation along the coast and the Coast Range valleys; the extent will be minimal. The upper level Rex Block is slowly developing overnight into Wednesday which will enhance the high pressure at the surface. While there is a ridge forming at the low levels, ensembles are still forming a midlevel trough at 500 mb. Closer to the surface, a strengthening thermal trough extending from the California Central Valley into south-central Oregon will induce cross barrier flow over the Casacdes and subsequent downsloping for the interior lowlands. This will send highs well into the 80s on Wednesday afternoon for areas away from the coast, with NBM probabilistic guidance indicating around a 35% chance to reach 90 degrees across the Portland metro area, and 15% in the central Willamette Valley. Temperatures will rise further on Thursday and Friday with much higher confidence for highs in the 90s. One shift from previous forecasts is the extent of these high temperatures. While they formerly covered mainly the greater Portland-Vancouver Metro and the western Columbia River Gorge, they have spread further south into the Willamette Valley, and the valleys of the Cascade Foothills. Heat risk is moderate for the urban areas north of Salem. .LONG TERM...Saturday through Tuesday...The Rex block slowly degrades on Saturday as a weak long-wave trough dips southward. Still will be warm and dry, but with incoming onshore flow, conditions will slowly improve. More substantial cooling should come on Sunday as WPC ensemble clusters show good agreement on the next upper level trough beginning to impact the Pacific Northwest, with temps back closer to seasonal norms in the low to mid 70s. Precipitation continues to see low probabilities as the core of the upper trough remains north over BC. Northwest Oregon and southwestern Washington will see the highest chances for rainfall, but again are minimal. -Muessle/CB && .AVIATION...Upper level troughing is expected to remain in place across the PNW which will maintain flow from the NW. Elongated surface high pressure stretches from the Gulf of Alaska to off the Oregon coast. The surface high is expected to slip southward tonight through Wednesday and will help maintain northerly surface winds between 5-10 kts on Wednesday. Winds along the coast could be a touch stronger around 12 kts along with gusts up to 20 kts tomorrow afternoon. CIGs should remain VFR into early tonight with scattered fair weather cumulus around 4 kft dissipating late this evening. HREF guidance suggests marine stratus developing (peak 40-50% chance) along the coast between 8-12Z and being maintained into Wednesday afternoon. HREF also suggests a bit of stratus developing along the Cascade Foothills around 10Z and dissipating by 17Z. There is a 30-40% chance that this impacts the terminals within the Willamette valley. PDX AND APPROACHES...VFR conditions should prevail through the TAF period with scattered cumulus around 4 kft into the evening. Winds will be from the NW around 5-10 kts, becoming light and variable overnight. There is a 30% MVFR CIGs develop around KTTD between 10-16Z and a 10% chance clouds make it to PDX. -Batz && .MARINE...Not much change as high pressure offshore is expected to persist through the week. Northerly winds around 15-20 kt will continue into this evening. A Small Craft Advisory will be in effect south of Cape Falcon through tonight. Expect will see periods of winds gusting up to 25 kt through Friday during the late afternoon and evenings. The northern zones are added tomorrow afternoon as winds increase across all waters. Small Craft Advisory is up through 11 PM Wednesday but will likely need to be extended later into the week. Seas around 4 to 6 feet will generally be wind driven through the week. A weak front is expected to approach the waters this weekend. -Batz/DH && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory from 2 PM to 11 PM PDT Wednesday for PZZ251-271. Small Craft Advisory until 11 PM PDT Wednesday for PZZ252-272. Small Craft Advisory until 11 PM PDT Wednesday for PZZ253-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland