Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
219 FXUS66 KPQR 090416 AAA AFDPQR Area Forecast Discussion...UPDATED National Weather Service Portland OR 916 PM PDT Mon Jul 8 2024 Updated Aviation Discussion .SYNOPSIS...This past weekend was hot, and it`s going to get hotter. The one exception to this is for those lucky enough to be along the coast, where sea breezes will keep it cooler. Otherwise, dangerous heat will continue through Tuesday with more triple digit heat. Temperatures are expected to peak for inland areas Tuesday, when highs could reach 105 degrees. A strong onshore push will bring some relief for Wednesday, keeping temps more moderate through the weekend. That said, we are still expecting it to be warmer than normal for the next 7-10 days, but the onshore flow should take Pac NW temps out of record territory beginning Wednesday. && .DISCUSSION...Monday night through Sunday night...Dangerously hot weather continues for all but the coast through Tuesday, with day after day of record breaking temperatures for much of the interior lowlands. KEY POINTS: 1. Record or near-record heat will persist inland through Tuesday. 2. High temperatures will likely reach 100-105 degrees over the Willamette and Hood River Valleys on Tuesday, similar to what has been observed thus far on Monday. 3. Tonight will be even slower to cool off in urban areas than the last several nights. Strengthening onshore flow will bring some relief to all locations Tuesday night into Wednesday, however temps will still be running above normal. 4. The prolonged and compounding nature of this heat wave will make it increasingly hard for people, pets, and plants to cope with the heat. This will especially be the case for those with medical conditions that make them sensitive to heat. A major HeatRisk continues over the interior lowlands. 5. Coastal areas will remain cooler, with highs generally in the 70s on Tuesday. Trending even cooler Wednesday onward. High temperatures finally reached 100 degrees at PDX on Sunday, July 7th after falling one degree short on July 5-6. Although this heat event won`t break the record for the highest number of consecutive days with max temps of 100 degrees or warmer at PDX, this record likely will be broken for Salem and Eugene when this heat wave is over with come Wednesday, as these two locations have observed high temps above 100 degrees from July 5-7 and are extremely likely to warm to 100 degrees or warmer on July 8-9 as well (85-90% chance). Despite PDX not breaking this particular record, this heat event will almost certainly tie the heat wave events that occurred in July 1941 and August 1981 for the most consecutive days at or above 99 degrees at Portland Airport with five days. So this heat wave still takes its place amongst the most significant heatwaves on record for the Willamette Valley, even for the Portland metro area. In addition to these records, many daily high temperature records have been broken as well; to view these, please refer to our Record Report (RER) via weather.gov/pqr. Note you will have to click on previous versions of our RER to find records broken for each day throughout this heat event. With temperatures in the evening starting off hotter later today and several days of heating in buildings and structures without air conditioning, Monday night will be the most brutal night of this event, especially for urban areas such as Portland and Salem where overnight relief looks very poor. NBM probabilistic guidance suggests a 50-60% chance Portland`s inner eastside and St Johns will not fall below 70 deg F Monday night and a 35-45% chance in Salem. Even if temps do dip into the upper 60s tonight, it would likely only be for one hour or less. After four days with high temps near 100 degrees or worse and limited overnight relief, Monday night and Tuesday have the potential to be the most dangerous portion of this prolonged heat event in regards to heat-related deaths and/or heat-related illnesses. This means it will still be a good idea to stay hydrated and out of the direct sun. Do not forget about any pets and/or outdoor plants you may have, as gardens will need frequent watering and pets will need plenty of water and shade. It will be best to walk dogs during the morning hours or late evening when temps will be relatively cooler and surfaces such as concrete and asphalt will no longer be hot enough to burn their paws. It never hurts to check on your friends, family, and neighbors as well if they do not have access to air conditioning. One little wrinkle to the forecast on Tuesday is some weak vorticity lifting northward from California, which will enhance instability over the Cascades. For locations west of the Cascades, forecast soundings show a fairly impressive stable layer between 900-800 mb, which will limit surface-based instability for locations west of the Cascades. While mid-level lapse rates steepen impressively and MUCAPE values increase, soundings continue to suggest we will not have enough moisture for thunderstorms to develop. At best, some cumulus clouds developing along and near the Cascade crest appear to be the most likely outcome. However, there may be some fire weather implications with the increasing instability, which is discussed below in the fire weather discussion. Low-level flow turns decisively onshore Tuesday night into Wednesday, bringing an end to the most intense heat. That said, WPC cluster analyses strongly suggest positive 500 mb height anomalies will last all the way through mid-July. This will keep the marine layer shallower than usual, and limit the effectiveness of onshore flow to cool inland areas. This will also make it very difficult for morning cloud cover to develop for inland areas away from the coast. So although the most extreme temps will be over with late this week into next weekend, don`t expect a refreshing blast of cool air unless you live along the coast or in the coastal valleys. Temperatures will likely remain 5-10 degrees above climatological averages through at least early next week (keep in mind climatological normals for high temps this time of year are in the lower 80s over the Willamette Valley). No rain is in sight for the foreseeable future. -TK/Weagle && .FIRE WEATHER...Monday afternoon through Tuesday...Issued a Red Flag Warning for fire weather zone 685 for Monday afternoon and early evening, which covers the southern Willamette Valley. This headline was issued due to breezy northerly winds expected over the south valley today with gusts up to 25 mph or so to the south of Salem, including the Eugene-Springfield area. Given these gusty winds will be occurring when relative humidity values are in the teens, any grass fire that does start will have the potential to spread rapidly towards the south. A similar setup is in store Tuesday afternoon, however winds are trending slightly weaker and are currently just shy of meeting our criteria for a Red Flag Warning. So, will hold off on issuing another Red Flag Warning over the south Valley for Tuesday afternoon, but will be watching trends closely. That said, fine dead fuels will be very receptive to ignition and spread, so it would not be surprising to see a few "median strip" type fires caused by careless smokers throwing their cigarette butts out their window while driving. Vehicles dragging chains and the like can also create sparks which have the potential to ignite wildfires. The bottom line is fire danger will still be significant on Tuesday and extreme caution should be exercised with fire, especially for inland areas below 2000 feet in elevation, where fuels are the driest. The other potential fire weather concern is in the high Cascades Tuesday afternoon. This is when model soundings continue to show steepening lapse rates in the presence of thermal low pressure, which can promote deeper columns in any fires which may start. However, after some coordination with fire partners and neighboring NWS WFOs, it appears our live 100-hr and 1000-hr fuels in the higher Cascades are not quite dry enough yet to support rapid fire spread if dry/unstable conditions were to materialize over the Cascades on Tuesday. Therefore, have decided to hold off on issuing any fire weather headlines in the Cascades. -TK && .AVIATION...Strong high pressure over the region will maintain VFR under clear skies, along with hot temperatures through Tuesday. As a result, expect the potential for high density altitude effects. As the air mass along the coast cools tonight, we`ll see see a 15-30% chance for patchy IFR conditions likely starting around 12Z Tuesday. Any lowered flight conditions that develop should scour out around 18Z Tuesday. PDX AND APPROACHES...VFR under clear skies as high pressure continues to dominant the airspace. /42 && .MARINE...High pressure well-offshore will maintain gusty northerly to northwesterly winds early this week. Tightening pressure gradients will lead to wind gusts up to 25 kt through Tuesday evening, mainly for the outer waters (10 to 60 NM out) between Cape Falcon and Florence, OR. Therefore, the Small Craft Advisory was extended for these locations through 8 PM Tuesday. Pressure gradients ease Tuesday night through early Wednesday afternoon, weakening winds below small craft conditions. Seas will mainly be wind-driven, between 3 to 5 feet. After mid-week, pressure gradients tighten again and northerly to northwesterly winds will likely (60-80% chance) re-strengthen to small craft conditions. This would build seas up to around 6 to 8 feet. -Alviz && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Excessive Heat Warning until 10 PM PDT Tuesday for ORZ104>125. Heat Advisory until 10 PM PDT Tuesday for ORZ126>128. WA...Excessive Heat Warning until 10 PM PDT Tuesday for WAZ202>210. Heat Advisory until 10 PM PDT Tuesday for WAZ211. PZ...Small Craft Advisory until 8 PM PDT Tuesday for PZZ272-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland