Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
436 FXUS66 KPQR 080945 CCA AFDPQR Area Forecast Discussion National Weather Service Portland OR 239 AM PDT Mon Jul 8 2024 .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 continues to build today and Tuesday; each day will be a couple degrees hotter than the last. 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...Today through Sunday...Dangerously hot weather continues for all but the coast, with day after day of record breaking temperatures for the interior. KEY POINTS: 1. Record or near-record heat will persist inland through Tuesday. 2. High temperatures will likely approach or reach 105 degrees for the Willamette and Hood River Valleys today and Tuesday. 3. Tonight will be even slower to cool off in urban areas than the last several. 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. 5. Coastal areas will remain cooler, with highs generally in the 70s through Tuesday. Trending even cooler Wednesday onward. High temperatures finally reached 100 degrees at PDX after two days of falling just a degree short. Although this won`t be a record-setting period of 100 degree temps for Portland, it probably will be for Salem and Eugene, both of which have exceeded 100 degrees for the last three days. This will, however, almost certainly tie heat waves in July 1941 and August 1981 for the most consecutive days at or above 99 degrees at Portland Airport with five. 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. Now that the NW flow has ended across BC and eastern WA, the Portland metro and SW Washington will be able to heat up a couple more degrees versus the past few. The 00z EC ensembles show good agreement with the 00z GFS deterministic that 850 mb temps will warm from around +22 deg C over Portland Sunday afternoon, to +24 to +25 deg C Monday afternoon. This suggests the potential for temperatures to be 3-5 degrees hotter for SW Washington and the Portland metro area than what has occurred the past few days. Would not be surprised to see a few Portland metro locations near 105 deg F this afternoon. Salem and Eugene already had 850 mb temps near +24 deg C on Sunday, so there will be little difference from Sunday to today for those locations - perhaps they will climb another degree or two to 105 deg F today and/or Tuesday. With temperatures starting off the evening hotter and several days of heating of buildings and structures, Monday night will probably be the most brutal of this event, especially for urban centers such as downtown Portland. NBM probabilistic guidance suggests a 50-70% chance Portland`s inner eastside and St Johns will not fall below 70 deg F Monday night. After 4 days of temps near 100 degrees or worse, with limited overnight relief, Monday night into Tuesday have the potential to be the most dangerous portion of this prolonged heat event. For probabilistic guidance from the latest NBM regarding high temps, refer to the probability-of-exceedance table shown below. Mon Tue Wed July 8 July 9 July 10 100+ 105+ 100+ 105+ 100+ 105+ ================================================ Kelso 70% 10% 75% 20% 0% 0% Portland* 90% 40% 99% 60% 5% 0% Salem 99% 55% 99% 75% 5% 0% Eugene 95% 40% 95% 40% 5% 0% Hood River 95% 45% 99% 80% 20% 1% The % of reaching 110 or higher is now at or less than 10% for all areas. Given the way this heat event has been trending, confidence is high we will NOT reach 110 degrees anywhere in the Willamette Valley. *Portland is for Greater Portland/Vancouver metro area. It is worth mentioning again that the worst of this heat wave looks to be today through Tuesday, so it will 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 cooler and surfaces such as concrete and asphalt will no longer be hot enough to burn their paws. 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. The steepening lapse rates in the presence of thermal low pressure may end up being more of a fire weather concern, as it 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. West of the Cascades, fine fuels are the main concern right now as those are most dry and ready to burn. There will be some increase in northerly winds Monday afternoon for the Willamette Valley and Coast Range, but it does not appear sufficient to meet Red Flag Warning criteria. 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, although there is no Red Flag Warning today, fire danger is still significant and extreme caution should be exercised with fire, especially for inland areas below 2000 feet in elevation, where fuels are the driest. 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. So although the worst will be over at that point, 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. No rain is in sight. Weagle && .AVIATION...Strong high pressure over the region will maintain clear skies, along with hot temperatures on Monday. As a result, expect the potential for high density altitude effects on takeoffs this afternoon into early evening. As the air mass along the coast cools tonight, will see patchy IFR stratus and fog re-form. Improvement to VFR likely by 16Z Monday. Northwest winds increase this afternoon along the coast with gusts to around 20 kt. PDX AND APPROACHES...High pressure will maintain VFR under clear skies. Northwest winds expected to increase to around 10 kt later this afternoon. /DH && .MARINE...Thermal low pressure just onshore extending southward along much of the coast. Meanwhile, high pressure remains anchored well offshore. This will maintain northerly winds on the waters into early this week. Building high pressure today tightens pressure gradients across the coastal waters with wind gusts up to 25 kt possible by late afternoon. Have issued a Small Craft Advisory for outer coastal waters south of Cape Falcon through tonight. Seas mostly a mix of wave fetches, one at 1 to 2 ft from the southwest, with the other from the west at 2 to 4 ft. As such, overall combined seas stay in the 3 to 5 ft range through mid-week. && .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 from 5 PM this afternoon to 5 AM PDT Tuesday for PZZ272-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland