Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
262 FXUS66 KPQR 012301 AAA AFDPQR Area Forecast Discussion National Weather Service Portland OR 400 PM PDT Mon Jul 1 2024 .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...Marine stratus continues to linger with IFR/MVFR conditions on the coast, and these lowered conditions are expected to slowly push offshore/scour out through 20Z Monday. These conditions are expected to return (50-80% probability) to the coast around 04Z-07Z Tuesday as a marine push is expected. Inland locations currently are seeing widespread VFR, with a few exceptions as MVFR conditions are currently impacting areas north of KSPB. Locations with lowered flight conditions are expected to improve to VFR around 20Z Monday. VFR conditions expected to dominant for inland locations through the remainder of the TAF period, with the exception of areas north of KSPB as a renewed marine push, could result in MVFR conditions along portions of the Columbia River. Could also see some backbuilding clouds off the Cascades, that could bring MVFR conditions (45%-65% probability) to KPDX and KTTD starting around 10Z Tuesday. Inland locations will also likely see northerly gusts up to 20 kt starting around 02Z Tuesday through 07Z Tuesday. PDX AND APPROACHES...MVFR conditions will improve to VFR through 19Z Monday. Northerly gusts up to 20 kt starting around 02Z Tuesday through 07Z Tuesday. Backbuilding clouds off the Cascades, that could bring MVFR conditions (45%-65% probability) to KPDX starting around 12Z Tuesday. /42 && .MARINE...Weak high pressure over the northeast Pacific with lower surface pressure over California and the Great Basin will more or less continue through the week. A weak front is in the process of passing through, but effects look fairly minimal, with light northwesterly winds through Monday morning. Afterwards, expect NNW winds across the waters as high pressure strengthens toward the middle of next week, with the strongest winds generally off the central coast of Oregon and lighter winds farther north. Winds will generally peak in the afternoon and evening hours each day. Small Craft Advisory remains on track for the central zones, but zones further to the north still look fairly marginal. Because as a thermal low develops along the northern California/southwest Oregon coast on Tuesday and strengthening/spreading north into Wednesday and thereafter. As a result will see an increase the pressure gradient along the coast and over the waters with a >90% chance that northerly wind gusts of 20-30 kt spread northward across the waters by mid week. This will in return develop steep wind driven seas of 5-8 ft with a dominant period of 7-8 seconds by late Tuesday or Wednesday. && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Wednesday for PZZ253-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland