National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Portland, OR

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605FXUS66 KPQR 030426 AAAAFDPQRArea Forecast Discussion...UPDATEDNational Weather Service Portland OR926 PM PDT Tue Jul 2 2024Aviation Discussion Updated....SYNOPSIS...Warm and dry conditions persist through mid weekbefore a drastic warmup begins Thursday. High pressureintensifies through the end of the week leading to dangerouslyhot temperatures through Sunday. Temperatures may moderateslightly to start next week but will remain hot well into nextweek.&&.SHORT TERM...Now through Wednesday Night...Sunny skies prevailacross most of the area this afternoon with the exception ofsome lingering marine cloud cover along the south Washington andfar north Oregon Coast. Observations show temperatures in the70s across most inland locations, while the marine influence isholding temps down in the 60s for coastal locations. In theupper levels, the region remains under dry northwest flow on theperiphery of strong high pressure centered well off theCalifornia coast which will become the dominant weather featurethrough the next seven days.Expect similarly pleasant conditions on Wednesday as the arearemains under the influence of northwest flow aloft. Inlandtemperatures will warm a few degrees into the low 80s as highpressure begins to shift closer to the coast, resulting inmodest 500 mb height rises and 850 mb temps climbing into the13-15 C range. /CB.LONG TERM...Thursday through Tuesday...A prolonged heatwavewill begin on Thursday as the strong upper level ridge over thePacific shifts closer to the coast and sends 850 mb temps intothe the low 20s Celsius. Current guidance has nudged inlandhighs upward into the mid 90s on Thursday afternoon, with arounda 20 percent chance to reach 100 degrees through the WillametteValley. Heat will peak Friday through Sunday as high pressurecontinues to build and shifts slowly inland near the CA/NVborder, with the ridge axis extending up the West Coast intonorthern BC. As a result, probabilities to surpass 100 degreesare above 70 percent across the interior lowlands both Fridayand Saturday and remain above 60 percent through Sunday. Thehighest temperatures of the week look to occur on Saturday ashighs are expected to climb to around 105 degrees in thelowlands. Notably, the probability to exceed 110 degrees rangesfrom 15-35 percent on Saturday, and around 10-15 percent bothFriday and Sunday. Overnight lows will also be running quitewarm, likely staying in the mid 60s or above and possiblystruggling to drop below 70 in the Portland metro Friday nightand Saturday night, limiting the amount of relief during theovernight hours. Given the high confidence in temperatures over100 and the duration of the event, have upgraded the ExcessiveHeat Watch to an Excessive Heat Warning from Thursday afternoonthrough Sunday evening. May need to consider adding the the HighCascades to the warning or placing them under an advisory infuture forecast cycles, but opted to delay that decision for nowas advisory level heat likely will not materialize in theCascades until Friday. In terms of historical context and giventhe low end probabilities to exceed 110 degrees, it is not outof the question that this event could rival the June 2021 eventor 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 temperatureswith minimal overnight relief, leading to dangerous conditionsthrough this weekend and possibly beyond.The ridge axis begins to shift east of the region Monday intoTuesday, but temperatures respond very slowly, only droppinginto the mid 90s and maintaining a 25 percent chance to hit 100degrees in many locations all the way through Tuesday. WPCensemble clusters also maintain strong ridging over the westernCONUS into the end of next week, with the Climate PredictionCenter keeping the region under a moderate risk for excessiveheat through July 12. So, although the hottest conditions areexpected through this weekend, people should be prepared to dealwith the cumulative effects of a long duration heat into atleast the middle of next week. /CB&&.AVIATION...

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Persistent high pressure over the region maintainsweak onshore flow. Widespread VFR conditions across the airspace,except for MVFR CIGs at KAST. Expect these flight conditions topersist through at least 10Z-12Z Wednesday. There may bebackbuilding of clouds along the Cascades around 12Z Wednesday,potentially bringing MVFR conditions (10-30% probability) toterminals north of KPDX, with KTTD having a higher probability(30-50%). Northwest winds with gusts up to 25 kt along the coastand 20 kt inland continue until around 06Z Wednesday, then becomelight thereafter.PDX AND APPROACHES...VFR conditions will persist through most ofthe period. Around 10Z Wednesday, backbuilding of clouds along theCascades could result in MVFR conditions (10-30% probability) inand around the terminal. Northwest winds with gusts up to 20 ktpossible until 06Z Wednesday, decreasing and remaining lightthrough the TAF period.-JH

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&&.MARINE...High pressure over the northeast Pacific with athermally induced low pressure over California/Oregon and theGreat 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 eachday with gusts up to 30 kt. Small Craft Advisory remains in place,and will likely to continue through much of the week. Marineconditions remain more wind driven resulting in 5 to 8 ft seasthrough the week. /42&&.PQR WATCHES/WARNINGS/ADVISORIES...

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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.

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