Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
159 FXUS66 KPQR 062208 AFDPQR Area Forecast Discussion National Weather Service Portland OR 308 PM PDT Sat Jul 6 2024 .SYNOPSIS...An ongoing heatwave will continue to impact locations away from the coast with record breaking temperatures through Tuesday due to strong high pressure aloft. Temperatures will trend cooler Wednesday into Thursday as onshore flow strengthens, bringing much needed relief to the area (especially during the overnight hours). A trickle of onshore flow may bring some cooling into the coastal valleys Sunday, but inland areas and elevations above 1000 ft will remain very hot. No rain is in sight through next weekend. && .DISCUSSION...Saturday night through Friday night...Minimal changes to the deterministic forecast this morning. NW Oregon and SW Washington remain within the grip of a prolonged and dangerous heat wave. Confidence is high the ongoing heatwave will continue impacting inland areas with triple digit high temperatures and poor overnight relief through Tuesday evening as a thermal trough deepens along and west of the Cascade crest. The deterministic NBM has remained quite consistent for high temps through Tuesday, suggesting highs will most likely top out around 100-105 degrees and low temps between 65-70 degrees across the Willamette Valley, Cowlitz Valley, Portland/Vancouver metro and Columbia River Gorge. The latest NBM probabilities have changed a bit in some locations, but not by very much (see table near the bottom of this discussion for the latest probabilities). With the thermal trough overhead, will not see all that much in way of winds. Despite the lack of wind, humidity values are way down at 10-20% for most inland locations each afternoon. Although it does not feel humid outside, the hot and dry conditions can easily result in dehydration for those who are not drinking enough water. Everyone should do their best to stay hydrated and avoid strenuous and/or prolonged outdoor activities to avoid heat exhaustion or heat stroke. This will be especially true between 11am-7pm when temperatures will be hottest. Got animals? Consider if they have adequate shade and water, and perhaps consider taking them out earlier in the day or in the evening when temperatures will be a bit cooler. Keep in mind that their paws can easily burn on hot surfaces like concrete and asphalt; another reason to take them out during the cooler morning hours. As always, never leave people or animals inside a hot car. Parking in the shade does not help enough during periods of extreme temperatures, nor does cracking your windows open. Anyone with outdoor plants/gardens will need to water frequently (ideally in the evening and/or early morning). Plants that are susceptible to sunburn should be shaded if possible. In addition to the hot afternoon temperatures, it still appears there will be minimal overnight relief as low temps will be running quite warm (especially in Portland, Salem, the Columbia River Gorge and the mid slopes of the Cascades). Keep in mind it will take quite some time for temperatures to fall each evening. Many lowlands areas may not see temperatures drop back under 90 until 7-8 pm (especially in urban areas). Overnight lows will likely fall back to the upper 50s to middle 60s for outlying rural area, however urban areas will struggle to dip much below 70 degrees. This is especially true Monday night when the probability for overnight lows above 70 degrees peak at 10-25%. The mid slopes of the Cascades will remain warm at night as well due to a temperature inversion, with some locations potentially seeing lows in the mid to upper 70s (10-25% chance). Will see a slight uptick of onshore flow Saturday night, enough to drop the coast back to more pleasant temperatures for Sunday. This means this heatwave event has essentially come to and end for the coast, as high temps will likely top out in the 70s Sunday through Tuesday. While that is still warmer than normal for the coast, this level of heat only warrants a minor HeatRisk. Meanwhile, inland valleys remain under a major to borderline extreme HeatRisk. As such, an Excessive Heat Warning remains in effect through Tuesday for locations away from the coast, aside from the Cascades which is under a Heat Advisory. For the Willamette Valley, the record number of days in a row with highs temps of 100 degrees of warmer is 5 days, set in mid-July 1941 at Portland airport. Many areas in the Willamette Valley/Clark County have seen 4 days in row a few times, such as back in August 2023, or 2015 or in 1981. For this heatwave, it looks like 4 days of 100+ deg heat is a good bet at PDX, but will see if the record 5 days is reached. Here are the odds of reaching 100+/105+ deg at select cities, based on the 19z iteration of the NBM on July 6th via the 1D Viewer: Sun Mon Tue Wed July 7 July 8July 9 July 10 100 105 100105 100 105 100 105 ======================================================== Kelso 50% 1% 60%20%45% 20% 0% 0% Portland* 75% 20% 80%40%80% 45% 0% 0% Salem 99% 65% 95%70%95% 75% 0% 0% Eugene 90% 25% 80%45%75% 25% 0% 0% Hood River 75% 5% 90%40%99% 50% 10% 0% The % of reaching 110 or higher is <5% for all areas, except on Tuesday when there is a 5-20% chance across the Willamette Valley (best chance in Salem, second best chance in Portland). *Portland is for Greater Portland/Vancouver metro area. The latest model guidance continues to suggest onshore flow will begin to increase Tuesday night into Wednesday as the thermal trough shifts east of the Cascades. This will bring westerly winds to the west side of the Cascades, with a modest cooldown for the interior for Wednesday. Overall, temperatures on Wednesday look to be in the upper 80s to middle 90s, but even cooler temperatures for Thursday and Friday with highs likely in the mid to upper 80s. Overnight lows will improve as well during that time, most likely falling into the mid to upper 50s (70-90% chance). -TK/Rockey/Weagle && .FIRE WEATHER...Hot and dry weather will rapidly dry out vegetation over the coming days. Unfortunately overnight relative humidity recoveries appear poor over the higher terrain for several nights moving forward, further working to chip away at fuel moisture. Forecast guidance still suggests winds will be lighter today and Sunday, but it will still be very hot, dry, and unstable near the surface with thermal low pressure overhead. Tuesday appears to be the most unstable day, and also the hottest day. Those working out on the line any day through Tuesday should pay special attention to staying hydrated, as the expected conditions can easily cause heat-related illness or worse. Onshore flow will strengthen Tuesday night into Wednesday, bringing the return of westerly winds, relatively cooler temperatures, and gradually improving humidities west of the Cascades. -Weagle/TK && .AVIATION...High pressure will maintain clear skies, with warm daytime temperatures. Expect high density altitude effects on takeoffs due to warm temperatures. Air mass along the coast cools later tonight, with pockets of IFR stratus and fog just onshore. PDX AND APPROACHES...High pressure maintaining clear skies/VFR flight conditions. && .MARINE...Not much in way of change. 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 next week. Gradients tight enough to pop gusts to near 20 kt in afternoons/evenings, but that will be generally south of Cascade Head today and again Sunday. Seas mostly a mix of wave fetches: one at 1 to 2 ft from the southwest, with the other from the west-northwest at 2 to 4 ft. As such, overall combined seas stay in the 3 to 4 ft range into early next 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...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland