Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
461 FXUS66 KPQR 020404 AAA AFDPQR Area Forecast Discussion National Weather Service Portland OR 905 PM PDT Mon Jul 1 2024 Updated aviation discussion .SYNOPSIS...Seasonable temperatures will continue through Wednesday as onshore flow continues. A very strong upper level ridge will then begin amplifying and moving into the Pacific Northwest beginning on the 4th of July, peaking in strength July 5-7. Confidence has increased for a significant heatwave during that time as the probability for high temps over 100 degrees has increased dramatically to 60-80% across the interior lowlands. && .SHORT TERM...Monday night through Wednesday night...The short term forecast is highlighted by an onshore flow pattern with varying degrees of morning cloud cover, afternoon sunshine, and seasonable temperatures. In fact, Tuesday is shaping up to be slightly cooler with high temps generally in the mid to upper 70s across the interior lowlands and 60s at the coast. Wednesday looks to feature similar temperatures, albeit a few degrees warmer. As has been the case over the past several days, northerly to northwesterly surface winds will increase a bit in the afternoon each day, especially across the southern Willamette Valley where winds will likely gust up to 20 mph. This includes the Eugene-Springfield area. Overnight lows each night look to range between 45-55 degrees, warmest over the Portland metro. This will offer excellent overnight relief for those without air conditioning. However, this relief will be short-lived as a significant heatwave is expected to impact the region from July 4-7, and possibly even beyond July 7th. This heatwave is discussed in more detail below. -TK && .LONG TERM...Thursday through Sunday night...The long term forecast is highlighted by a significant heatwave with record breaking temperatures now likely to occur. HeatRisk is now in the moderate to major category across all of northwest Oregon and southwest Washington, except for the coast where weak onshore flow looks to maintain much cooler temperatures when compared to inland locations. Before getting into the temperature forecast, would first like to discuss the synoptic scale setup in place. Models and their ensembles are now honed in on an upper level ridge amplifying over the western CONUS July 4-7, peaking in strength July 5-7. It appears an omega blocking pattern will develop during that time due to a closed upper level low over the northeast Pacific and another over the Northern Plains into the Great Lakes region. These two lows will help keep the ridge over the western CONUS locked in place for at least three to four days, potentially even longer than that. With this impressive ridge in place, temperatures will become abnormally hot with record breaking high temperatures now likely to occur. The latest suite of model guidance continues trending warmer, with widespread high temps in the lower 100s for most valley locations away from the coast likely by July 5-6 according to the deterministic NBM. In fact, the probability for high temperatures above 100 degrees has increased dramatically to 60-80%. The warmest ensemble members from the EPS/GEFS suggest high temps close to 110 degrees or warmer, and the NBM is now showing a 15-30% chance for high temps of 110 degrees or warmer. Regardless of whether high temps wind up near 100, 105, or 110, it will be more than hot enough for people to suffer from heat exhaustion or heat stroke if outdoors for a prolonged period of time, or for people who are indoors with no air conditioning. This has helped push HeatRisk into the major category for the entire Portland metro, Salem, Eugene, Columbia River Gorge and Upper Hood River Valley. A major HeatRisk means anyone without effective cooling and/or adequate hydration will be impacted, especially those who are particularly sensitive to heat. Be sure to do everything you can to stay cool during the upcoming heatwave, and don`t forget to check on your neighbors and loved ones from time to time. Lastly, never leave pets or people inside a hot car, and ensure your pets stay cool during this heatwave as well. Walking your dog in the afternoon will not be a good idea as their paws may easily burn. It`s also worth mentioning that overnight lows are looking quite warm with minimal overnight relief. As of right now, overnight lows will likely wind up in mid 60s to lower 70s. -TK && .AVIATION...High pressure will persist across the region with increasing northwest flow aloft. Onshore flow expected to maintain marine stratus at the coast with predominately MVFR cigs, although a 20% chance of IFR through 18Z Tue. Predominately VFR inland through the period, with the exception for increasing chances of MVFR CIGS developing by 12-14Z Tue and persisting through 18Z Tue as morning clouds build. Highest chances (50-70%) along the Columbia River. Northwest winds expected to increase by Tue afternoon with gusts up to 20-25 kt. PDX AND APPROACHES...Predominately VFR expected. However, backbuilding clouds off the Cascades could (40-70% chance) bring MVFR cigs to PDX and TTD between 12-18Z Tuesday morning. Northwest winds around 10-12 kt expected to ease overnight to around 4-6 kt. /DH && .MARINE...Weak high pressure over the northeast Pacific with lower surface pressure over California and the Great Basin will persist through the week. NNW winds across all waters as high pressure strengthen. Winds will generally peak in the afternoon and evening hours each day with gusts up to 25 kt. Therefore, have adjusted the current Small Craft Advisory to now include all waters. Because the thermal surface low will strengthen through the middle of the week, will likely see (75%-90% probability) northerly wind gusts up to 30 kt for zones PZZ272, 273, 252 and 253 by the middle of the week. In addition to the elevated winds, seas will become more wind driven and build towards 7 to 9 ft by tonight and look to hold there through the week. /42 && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Excessive Heat Watch from Thursday afternoon through Sunday evening for ORZ104>125. WA...Excessive Heat Watch from Thursday afternoon through Sunday evening for WAZ202>210. PZ...Small Craft Advisory until 11 PM PDT Tuesday for PZZ251>253- 271>273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland