Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
454 FXUS66 KPQR 022223 AFDPQR Area Forecast Discussion National Weather Service Portland OR 323 PM PDT Tue Jul 2 2024 .SYNOPSIS...Warm and dry conditions persist through mid week before a drastic warmup begins Thursday. High pressure intensifies through the end of the week leading to dangerously hot temperatures through Sunday. Temperatures may moderate slightly to start next week but will remain hot well into next week. && .SHORT TERM...Now through Wednesday Night...Sunny skies prevail across most of the area this afternoon with the exception of some lingering marine cloud cover along the south Washington and far north Oregon Coast. Observations show temperatures in the 70s across most inland locations, while the marine influence is holding temps down in the 60s for coastal locations. In the upper levels, the region remains under dry northwest flow on the periphery of strong high pressure centered well off the California coast which will become the dominant weather feature through the next seven days. Expect similarly pleasant conditions on Wednesday as the area remains under the influence of northwest flow aloft. Inland temperatures will warm a few degrees into the low 80s as high pressure begins to shift closer to the coast, resulting in modest 500 mb height rises and 850 mb temps climbing into the 13-15 C range. /CB .LONG TERM...Thursday through Tuesday...A prolonged heatwave will begin on Thursday as the strong upper level ridge over the Pacific shifts closer to the coast and sends 850 mb temps into the the low 20s Celsius. Current guidance has nudged inland highs upward into the mid 90s on Thursday afternoon, with around a 20 percent chance to reach 100 degrees through the Willamette Valley. Heat will peak Friday through Sunday as high pressure continues to build and shifts slowly inland near the CA/NV border, with the ridge axis extending up the West Coast into northern BC. As a result, probabilities to surpass 100 degrees are above 70 percent across the interior lowlands both Friday and Saturday and remain above 60 percent through Sunday. The highest temperatures of the week look to occur on Saturday as highs are expected to climb to around 105 degrees in the lowlands. Notably, the probability to exceed 110 degrees ranges from 15-35 percent on Saturday, and around 10-15 percent both Friday and Sunday. Overnight lows will also be running quite warm, likely staying in the mid 60s or above and possibly struggling to drop below 70 in the Portland metro Friday night and Saturday night, limiting the amount of relief during the overnight hours. Given the high confidence in temperatures over 100 and the duration of the event, have upgraded the Excessive Heat Watch to an Excessive Heat Warning from Thursday afternoon through Sunday evening. May need to consider adding the the High Cascades to the warning or placing them under an advisory in future forecast cycles, but opted to delay that decision for now as advisory level heat likely will not materialize in the Cascades until Friday. In terms of historical context and given the low end probabilities to exceed 110 degrees, it is not out of the question that this event could rival the June 2021 event or certainly the August 2023 event in terms of magnitude. Regardless of exactly how high temperatures ultimately climb, confidence is high in a prolonged period of hot temperatures with minimal overnight relief, leading to dangerous conditions through this weekend and possibly beyond. The ridge axis begins to shift east of the region Monday into Tuesday, but temperatures respond very slowly, only dropping into the mid 90s and maintaining a 25 percent chance to hit 100 degrees in many locations all the way through Tuesday. WPC ensemble clusters also maintain strong ridging over the western CONUS into the end of next week, with the Climate Prediction Center keeping the region under a moderate risk for excessive heat through July 12. So, although the hottest conditions are expected through this weekend, people should be prepared to deal with the cumulative effects of a long duration heat into at least the middle of next week. /CB && .AVIATION...High pressure anchored over the region will persist along with weak onshore flow. Widespread VFR conditions across the airspace with the MVFR conditions at KAST currently the only exception. Expect these flight conditions to persist through at least 10Z-12Z Wednesday as backbuilding clouds along the Cascades could bring MVFR conditions (30%-40% probability) to terminals north of KPDX Northwest winds will persist with gusts up to 25 kt along the coast and up to 20 kt for inland locations through 07Z Wednesday. PDX AND APPROACHES...VFR conditions will persist through around 10Z Wednesday as backbuilding clouds could result in MVFR conditions (25%-35% probability) in and around the terminal. Northwest winds persist with gusts up to 20 kt possible through 07Z Wed. /42 && .MARINE...High pressure over the northeast Pacific with a thermally induced low pressure over California/Oregon and the Great Basin, which will persist through the remainder of the week. This will result in north/northwest winds across all waters. Winds will generally peak in the afternoon and evening hours each day with gusts up to 30 kt. Small Craft Advisory remains in place, and will likely to continue through much of the week. Marine conditions remain more wind driven resulting in 5 to 8 ft seas through the week. /42 && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Excessive Heat Warning from noon Thursday to 11 PM PDT Sunday for ORZ104>125. WA...Excessive Heat Warning from noon Thursday to 11 PM PDT Sunday for WAZ202>210. PZ...Small Craft Advisory until midnight PDT tonight for PZZ251>253. Small Craft Advisory until 3 AM PDT Wednesday for PZZ271>273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland