National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Portland, OR

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-- Discussion containing changed information from previous version are highlighted. --265FXUS66 KPQR 072155 CCAAFDPQRArea Forecast DiscussionNational Weather Service Portland OR253 PM PDT Sun Jul 7 2024.SYNOPSIS...Northwest Oregon and southwest Washington remain withinthe grip of a prolonged heat wave that will persist through Tuesday.The strong ridge of high pressure aloft responsible for our heat wavewill slowly migrate eastward over the coming days. As it does so,thermal low pressure will focus on areas east of the Cascades,allowing onshore flow to strengthen Tuesday night and Wednesday. Thiswill bring an end to the record hot temperatures, but above normaltemps are very likely to persist through the end of the week. No rainis expected through next weekend.&&.SHORT TERM...
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Sunday night through Tuesday night...The overallforecast picture has changed little over the last 48 hours, andremains on track for oppressive heat to persist from the Coast Rangeeastward through Tuesday. For those who may not have time to readthrough this full discussion, please refer to our key points belowfor a quick summary:KEY POINTS:1. Record or near-record heat will persist inland through Tuesday.2. High temperatures will likely approach or reach 105 degrees forthe Willamette and Hood River Valleys Monday and Tuesday.3. Nights will be slow to cool off in urban areas through Mondaynight. Strengthening onshore flow will bring some relief to alllocations Tuesday night into Wednesday, however temps will still berunning above normal.4. The prolonged and compounding nature of this heat wave will makeit increasingly hard for people, pets, and plants to cope with theheat. This will especially be the case for those with medicalconditions that make them sensitive to heat.5. Coastal areas will remain cooler, with highs generally in the 70sthrough Tuesday. Trending even cooler Wednesday onward.Confidence continues to increase that Tuesday night will be thedefinitive end to this heat event for inland areas as onshore flowincreases and begins to moderate temperatures. Excessive heat hasalready come to an end for coastal communities as observedtemperatures early Sunday afternoon were generally in the 70s fromAstoria to Tillamook. Temps were around 65-70 degrees on the LongBeach Peninsula. Even cooler temps were being observed south ofTillamook, especially from Newport to Florence where temps were inthe upper 50s to mid 60s with a broken marine stratus deck over thecoastal waters attempting to push slightly onshore. Similar temps areexpected at the coast Monday, then trending cooler Tuesday throughThursday as onshore flow persists. Despite the relatively coolertemps at the coast, excessive heat will persist for inland areasthrough Tuesday with widespread high temps generally ranging between100-105F and morning lows between 60-70F (warmest in urban areas). Inaddition, poor overnight relief is expected Monday night with tempsrunning noticeably warmer when compared to what has been observedover the past few nights. NBM probabilities for low temps of 70degrees or warmer are at 40-60% for the Portland metro and Salem, butmuch lower elsewhere. For probabilistic guidance from the latest NBMregarding high temps, refer to the table shown below. Noteprobabilities have generally decreased a bit from yesterday. Mon Tue Wed July 8 July 9 July 10 100 105 100105 100 105 =========================================Kelso 65% 20% 55%10% 1% 0%Portland* 90% 45% 80%50% 10% 0%Salem 90% 50% 80%60% 20% 0%Eugene 90% 40% 80%30% 5% 0%Hood River 95% 50% 95%65% 20% 0%The % of reaching 110 or higher is now at or less than 10% for allareas. Given the way this heat event has been trending, confidence ishigh we will NOT reach 110 degrees anywhere in the Willamette Valley.*Portland is for Greater Portland/Vancouver metro area.It is worth mentioning that the worst of this heat wave looks to beMonday through Tuesday, so it will be a good idea to stay hydratedand out of the direct sun. Do not forget about any pets and/oroutdoor plants you may have, as gardens will need frequent wateringand pets will need plenty of water and shade. It will be best to walkdogs during the morning hours or late evening when temps will becooler and surfaces such as concrete and asphalt will no longer behot enough to burn their paws.For the Willamette Valley, the record number of days in a row withhighs temps of 100 degrees of warmer is 5 days, set in mid-July 1941at the Portland Airport. Many areas in the Willamette Valley/ClarkCounty have seen 4 days in row a few times, such as back in August2023, or 2015 or in 1981. For this heatwave, it looks like 4 days of100+ deg heat is a good bet at Salem and Eugene, but will see if therecord 5 days is reached. Portland has just missed 100F by one degreethe past two afternoons, so it is now clear this particular recordwill not be broken at the Portland Airport.One little wrinkle to the forecast on Tuesday is some weak vorticitylifting northward from California, which will enhance instabilityover the Cascades. For locations west of the Cascades, forecastsoundings show a fairly impressive stable layer between 900-800 mb,which will limit surface-based instability for locations west of theCascades. While mid-level lapse rates steepen impressively and MUCAPEvalues increase, soundings continue to suggest we will not haveenough moisture for thunderstorms to develop. At best, some cumulusclouds developing along and near the Cascade crest appear to be themost likely outcome. The steepening lapse rates in the presence ofthermal 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 neighboringNWS WFOs, it appears our live 100-hr and 1000-hr fuels in the higherCascades are not quite dry enough yet to support rapid fire spread ifdry/unstable conditions were to materialize over the Cascades onTuesday. West of the Cascades, fine fuels are the main concern rightnow as those are most dry and ready to burn, however a lack of windin the forecast suggests concerns regarding the potential for rapidfire spread is low. Therefore, there are no immediate fire weatherconcerns at this time and the fire weather discussion has beenremoved from our Area Forecast Discussion as a result of that.Instead, please refer to our Fire Weather Planning forecast if youare searching for more detail regarding our fire weather forecast.-TK
-- End Changed Discussion --&&.LONG TERM...Wednesday through Saturday night...In regards to theweather forecast for Wednesday through Saturday, there are no majorconcerns at this time as varying degrees of onshore flow willprevent extreme heat from persisting or redeveloping. That said,models and their ensembles continue to suggest temps will at the veryleast remain above normal through Saturday with high temps mostlikely winding up somewhere between 85-95 degrees each day. Theprobability for high temps above 95F is fairly low Wednesday throughThursday at around 25% or less over the Willamette Valley andPortland metro; the one exception to that is on Wednesday whenprobabilities range between 30-70%. Conditions are very likely toremain dry through next Saturday as NBM PoPs are at 0% across all ofsouthwest WA and northwest OR. -TK&&.AVIATION...Little change. Strong high pressure over the regionwill maintain clear skies, along with hot temperatures into theearly evening. As a result, expect the potential for high densityaltitude effects on takeoffs this afternoon into early evening.Patchy stratus along the Oregon coast will dissipate thisafternoon. But, as the air mass along the coast cools tonight,will see patchy IFR stratus and fog re-form.PDX AND APPROACHES...High pressure will maintain VFR under clearskies.&&.MARINE...Not much in way of change. Thermal low pressure justonshore extending southward along much of the coast. Meanwhile,high pressure remains anchored well offshore. This will maintainnortherly winds on the waters into early this week. Gradientstight enough to pop gusts to near 20 kt through early thisevening, mainly south of Cascade Head. High pressure builds onMonday, tightening pressure gradients with wind gusts up to 25 ktpossible by Monday afternoon. 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 inthe 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/portlandInteract with us via social media:www.facebook.com/NWSPortlandwww.twitter.com/NWSPortland