National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Portland, OR

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-- Discussion containing changed information from previous version are highlighted. --380FXUS66 KPQR 040405 AAAAFDPQRArea Forecast Discussion...UPDATEDNational Weather Service Portland OR905 PM PDT Wed Jul 3 2024Aviation Discussion Updated....SYNOPSIS...Dry and warm through Thursday. High pressureintensifies through the end of the week leading to dangerouslyhot temperatures through at least Sunday. Temperatures maymoderate slightly to start next week but will remain hot wellinto next week.&&.SHORT TERM...Now through Thursday night...Minimal changes inthe forecast as high pressure begins to build over our area.Cloud cover has dissipated across most of the CWA, except forportions of the south Washington coast. Enjoy the pleasantweather this afternoon/evening while it lasts! Tomorrow will bethe first day of the more persistent warm up as temperaturesrise into the low 90s for interior valleys and 70s along thecoast 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 windsto become more north to northeasterly. The GFS on the other handdoesn`t have the thermal trough forming just yet, but eitherway our air mass will begin to warm up with the ridge buildingover us.The Excessive Heat Warning remains in effect beginning 12 PM PDTtomorrow due to a combination of the initial stages of the hightemperatures but also the effects of it being a holiday weekend.We have also added a Heat Advisory for all of the Cascadesconsidering 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 lookingat an intensifying ridge taking on the omega blocking patternas a trough digs southward to the west over the Pacific, and tothe east over the Rockies. This ridge will amplify throughSunday which will lead to a prolonged, dangerous heatwave.There have been minimal changes in the temperatures overall andthe pattern seems to be consistent. Fortunately, winds do notlook overly impactful in the long term.Friday, Saturday, and Sunday are forecast to be the hottestdays, with temperatures soaring to 100 to 105 degrees F forinterior lowland valleys. The Excessive Heat Warning will gothrough the entire 4th of July weekend as there will bewidespread major HeatRisk across northwest Oregon and southwestWashington, west of the Cascades. Overnight temperatures willalso struggle to cool down, with lows forecast between 65 to 70deg F within interior valleys from Saturday morning to at leastMonday morning. Heat exhaustion or heat stroke is possible foranyone who is exposed to the heat without an effective way tocool down, especially those who are particularly susceptible toheat.Some regions that are a concern, but will remain outside of theExcessive Heat Warning are the Cascades. As it stands,temperatures remain mostly within moderate HeatRisk, andafternoon highs will struggle to climb as high due to shadingfrom the local vegetation type. However, if you`re out hikingor camping this weekend, the risk for heat related illnesses isnon-zero. Thus, the reason why we decided to add a Heat Advisoryfor the Cascades beginning 12 PM PDT tomorrow. Please practicesafe 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 (specificallyaround Portland) are resembling the heatwaves we saw in lateJuly of 2009 and last August of 2023. We saw a few days ofhighs in the 90s, highs around 100-105 for about 3 days,followed by a return to the 90s for more days. Regardless ofexactly how high temperatures ultimately climb, confidence ishigh in a prolonged period of hot temperatures with minimalovernight relief, leading to dangerous conditions through thisweekend and possibly into early next week.The ridge axis begins to shift east of the region Monday intoTuesday, but temperatures respond very slowly, only droppinginto the mid to upper 90s in many locations all the way throughTuesday. WPC ensemble clusters also maintain strong ridgingover the western CONUS into the end of next week, with theClimate Prediction Center keeping the region under a moderaterisk (40% chance) for excessive heat through July 12. So,although the hottest conditions are expected through thisweekend, people should be prepared to deal with the cumulativeeffects of a long duration heat into at least the middle of nextweek. -Alviz/Muessle&&.AVIATION...
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High pressure persists, with weak onshore flow.VFR conditions are expected along the coast, except for KAST withMVFR/IFR conditions possible (35-45% probability) startingbetween 07-17Z Thursday. These lowered flight conditions along thecoast will likely be somewhat short lived as northerly/slighteasterly winds develop around 13-15Z Thursday.Generally VFR for inland terminals through the remainder of theTAF period, with NW flow between 5-10 kt. Gusts around 20 kt areexpected to return each afternoon and persist through the evening.PDX AND APPROACHES...VFR conditions for the rest of the TAFperiod.-JH
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High pressure over the northeast Pacific with athermally induced low pressure over California/Oregon and theGreat Basin. This pattern will persist through the remainder ofthe week and likely into the start of next week. Small CraftConditions will develop across all the waters, with a brief pausein conditions late tonight and into early Thursday morning.Expect gusts up to 30 kt with similar conditions each afternoonand evening as winds will closely follow a diurnal cycle. Seaswill be predominately wind-driven resulting in 5-8 ft at 8-10seconds throughout the week. /42
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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.
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