Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
060 FXUS66 KPQR 031038 AFDPQR Area Forecast Discussion National Weather Service Portland OR 338 AM PDT Wed Jul 3 2024 .SYNOPSIS...Dry and warm through 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 Thursday...Minimal change in the forecast as the high pressure ridge builds today. Will see sunny skies 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 in the morning. 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. Thursday will be the first day of the more persistent warm up as temperatures rise generally into the 90s for the 4th of July holiday. While not necessarily as hot as we will see over the weekend, the thermal trough will develop causing winds to become north to northeasterly. This will "shut off" the northwesterly flow aloft and thus cause even more warming at the mid-elevations. The Excessive Heat Warning starts on Thursday due to a combination of the initial stages of the high temperatures but also the effects of it being a holiday weekend. Know that if you`re planning on going near rivers and lakes, they are still on the chillier side. -Muessle/CB .LONG TERM...Friday through Tuesday...Synoptically, 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 heatwave. There have been minimal changes in the temperatures overall and the pattern seems to be consistent. Looking at Friday, Saturday, and now Sunday being the warmer days, with the highest temperatures on Saturday. Lower elevations will see the highest values near 105 deg F. The Excessive Heat Warning remains in effect as major HeatRisk encompasses much of the forecast area. Some regions that are a concern, but will remain outside of the warning are the Cascades. As it stands, temperatures are in moderate HeatRisk, and due to vegetation type, will struggle to see as high of daytime temperatures due to shading from the solar radiation. However, if you`re out hiking or camping this weekend, the risk for heat related illnesses is non-zero. Please practice safe procedures like drinking ample water, taking breaks often, and minimizing alcohol consumption. For inland and Cascade valleys, probabilities for temperatures greater than 105 deg F range from 20-50% on Friday and 60-80% on Saturday. On both days, the highest probabilities lie along the I-5 corridor at elevations below 300 ft. Sunday`s probabilities have seen little change but the highest chances (around 70%) continue to be within urban areas around Salem, Hillsboro, Portland, Vancouver, etc. The Columbia River Gorge, especially around Hood River will see around a 50% chance of 105 deg F or more on Sat/Sun. The probability for temperatures greater than 110 deg F remain less than 25% on Saturday with Friday and Sunday being minimal. Based on some brief research, temperatures forecast - specifically around Portland - are resembling the heatwave we saw in late July of 2009. We saw a few days of highs in the 90s, with low 100s for 2 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 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 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. -Muessle/CB && .AVIATION...High pressure continues, with generally weak onshore flow continuing for the near future. Marine stratus continues to be the dominant impact at coastal terminals during nighttime hours, with MVFR CIGS at KAST. KONP looks to trend VFR for the rest of the night, as it looks like marine stratus is staying offshore. KAST should remain MVFR until 18-20z, after which it clears up and turn to VFR throughout daytime hours Wed. Coastal terminals see only around a 20% chance of MVFR thresholds late in the TAF period Wed night, as an increasing thermal trough may switch flow offshore, keeping marine stratus off shore. Most inland terminals will remain VFR throughout the period, with light NW flow between 5-10 kt. The exceptions are KPDX and KTTD, which could see some marine stratus building off the Cascades. Currently around a 50-70% chance of high-end MVFR cigs between 12-18z Wed, after which it should clear up quickly. VFR conditions dominate the rest of the TAF period. PDX AND APPROACHES...Brief period of possible high-end MVFR cigs due to marine stratus backbuilding off the Cascades between 12-18z. Around a 50-70% chance of cigs dropping to around 2500 ft. Afterwards, VFR conditions return for the rest of the TAF period. NW winds between 5-10 kt expected throughout the TAF period. -JLiu && .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. The previous Small Craft Advisory has ended, but a few stray gusts up to 25 kt will still be possible for another hour or so, until 4-5am Wed. SCA conditions return early Wednesday afternoon to the central and southern waters, with gusts up to 30 kt possible as the thermal trough enhances winds. Expect similar conditions each afternoon and evening as winds will closely follow a diurnal cycle of stronger gusts up to 30 kt during afternoon/evening hours, and decreasing below SCA criteria overnight and during early morning hours. Expect wind-driven seas between 5-8 ft at 8 seconds throughout much of the week. -JLiu && .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 from 1 PM this afternoon to 11 AM PDT Thursday for PZZ252-253-272-273. Small Craft Advisory until 3 AM PDT early this morning for PZZ271>273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland