Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
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380 FXUS66 KPQR 040405 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 905 PM PDT Wed Jul 3 2024 Aviation Discussion Updated... .SYNOPSIS...Dry and warm through Thursday. High pressure intensifies through the end of the week leading to dangerously hot temperatures through at least Sunday. Temperatures may moderate slightly to start next week but will remain hot well into next week. && .SHORT TERM...Now through Thursday night...Minimal changes in the forecast as high pressure begins to build over our area. Cloud cover has dissipated across most of the CWA, except for portions of the south Washington coast. Enjoy the pleasant weather this afternoon/evening while it lasts! Tomorrow will be the first day of the more persistent warm up as temperatures rise into the low 90s for interior valleys and 70s along the coast for the 4th of July holiday. While not necessarily as hot as what we will see this weekend, the Euro model is showing a thermal trough developing tomorrow (Thursday) which would "shut off" onshore flow and cause winds to become more north to northeasterly. The GFS on the other hand doesn`t have the thermal trough forming just yet, but either way our air mass will begin to warm up with the ridge building over us. The Excessive Heat Warning remains in effect beginning 12 PM PDT tomorrow due to a combination of the initial stages of the high temperatures but also the effects of it being a holiday weekend. We have also added a Heat Advisory for all of the Cascades considering those who may have travel plans in the mountains. Know that if you`re planning on going near rivers and lakes, they are still on the chillier side. -Alviz/Muessle && .LONG TERM...Friday through Tuesday...Synoptically, we`re looking at an intensifying ridge taking on the omega blocking pattern as a trough digs southward to the west over the Pacific, and to the east over the Rockies. This ridge will amplify through Sunday which will lead to a prolonged, dangerous heatwave. There have been minimal changes in the temperatures overall and the pattern seems to be consistent. Fortunately, winds do not look overly impactful in the long term. Friday, Saturday, and Sunday are forecast to be the hottest days, with temperatures soaring to 100 to 105 degrees F for interior lowland valleys. The Excessive Heat Warning will go through the entire 4th of July weekend as there will be widespread major HeatRisk across northwest Oregon and southwest Washington, west of the Cascades. Overnight temperatures will also struggle to cool down, with lows forecast between 65 to 70 deg F within interior valleys from Saturday morning to at least Monday morning. Heat exhaustion or heat stroke is possible for anyone who is exposed to the heat without an effective way to cool down, especially those who are particularly susceptible to heat. Some regions that are a concern, but will remain outside of the Excessive Heat Warning are the Cascades. As it stands, temperatures remain mostly within moderate HeatRisk, and afternoon highs will struggle to climb as high due to shading from the local vegetation type. However, if you`re out hiking or camping this weekend, the risk for heat related illnesses is non-zero. Thus, the reason why we decided to add a Heat Advisory for the Cascades beginning 12 PM PDT tomorrow. Please practice safe procedures like drinking ample water, taking breaks often, and minimizing alcohol consumption. Here are temperature probabilities for the Willamette Valley, where the most intense heat is expected: Greater than or equal to 100 degrees: 70-90% Greater than or equal to 105 degrees: 50-60% Greater than or equal to 110 degrees: 25-30% Greater than or equal to 115 degrees: 5-10% Based on some brief research, forecast temperatures (specifically around Portland) are resembling the heatwaves we saw in late July of 2009 and last August of 2023. We saw a few days of highs in the 90s, highs around 100-105 for about 3 days, followed by a return to the 90s for more days. 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 into early next week. The ridge axis begins to shift east of the region Monday into Tuesday, but temperatures respond very slowly, only dropping into the mid to upper 90s 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 (40% chance) 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. -Alviz/Muessle && .AVIATION...High pressure persists, with weak onshore flow. VFR conditions are expected along the coast, except for KAST with MVFR/IFR conditions possible (35-45% probability) starting between 07-17Z Thursday. These lowered flight conditions along the coast will likely be somewhat short lived as northerly/slight easterly winds develop around 13-15Z Thursday. Generally VFR for inland terminals through the remainder of the TAF period, with NW flow between 5-10 kt. Gusts around 20 kt are expected to return each afternoon and persist through the evening. PDX AND APPROACHES...VFR conditions for the rest of the TAF period. -JH && .MARINE...High pressure over the northeast Pacific with a thermally induced low pressure over California/Oregon and the Great Basin. This pattern will persist through the remainder of the week and likely into the start of next week. Small Craft Conditions will develop across all the waters, with a brief pause in conditions late tonight and into early Thursday morning. Expect gusts up to 30 kt with similar conditions each afternoon and evening as winds will closely follow a diurnal cycle. Seas will be predominately wind-driven resulting in 5-8 ft at 8-10 seconds throughout the week. /42 && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Excessive Heat Warning from noon Thursday to 11 PM PDT Sunday for ORZ104>125. Heat Advisory from noon Thursday to 11 PM PDT Sunday for ORZ126>128. WA...Excessive Heat Warning from noon Thursday to 11 PM PDT Sunday for WAZ202>210. Heat Advisory from noon Thursday to 11 PM PDT Sunday for WAZ211. PZ...Small Craft Advisory until 3 AM PDT Thursday for PZZ252-253-271. Small Craft Advisory until 5 AM PDT Friday for PZZ272-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland