textproduct: Portland

SYNOPSIS

Temperatures embark on a bit of a "roller-coaster" ride over the next 5-7 days highlighted by significant warm-up into early next week. This will support widespread Moderate HeatRisk across northwest Oregon and southwest Washington, with localized Major HeatRisk across the Portland-Vancvouer Metro Area through the Columbia River Gorge. An Extreme Heat Watch is now in effect for the latter two locations Monday through Tuesday evening. There remains some uncertainty come Wednesday as to just how quickly the heat diminishes but confidence is increasing for a return to slightly cooler temperatures by Thursday and Friday of next week.

DISCUSSION...Now through Thursday

This afternoon the axis of a weak high pressure ridge is beginning to shift further to our east but not before temperatures across the inland valleys centered along the I-5 corridor rise into the mid to upper 80s. At least if you think mid to upper 80s are too warm for your liking some relief is slated for tomorrow (Saturday). Satellite imagery depicts marine stratus entrenched along a good chunk of the Oregon coast spurred on by the southern periphery of an approaching upper-level shortwave trough. While the core of this upper trough likely swings down into southern British Columbia and Alberta tonight into Saturday, the progression of this feature will noticeably increase westerly onshore flow regionally. With the aforementioned westerly flow in addition to some morning cloud cover filtering into the inland valleys, high temperatures on Saturday generally rise mid to upper 70s - about 10 degrees cooler than the day prior (today).

It's worth noting the passing trough tightens the west to east surface pressure gradient across the Cascades on Saturday leading to locally breezy/windy conditions through portions of the Columbia Gorge. The strongest west winds are locally expected through the central Columbia River Gorge and Upper Hood River Valley, where westerly winds may gust up to 30-40 mph with a 20-30% chance for infrequent wind gusts to exceed 45 mph. These winds noticeable decrease Saturday night.

The second half of the weekend temperatures begin to rebound into the mid to upper 80s Sunday afternoon as ensemble guidance shows the upper-trough quickly shifting eastward and upper- level ridging rebuilding offshore over the northeast Pacific. The hottest days over the next week are expected on Monday and Tuesday during which the vast majority of ensemble members show the ridge sliding right over-top the Pacific Northwest. There is high confidence (>95% chance) for high temperatures exceeding 90 degrees F across the Willamette Valley and southwest Washington lowlands on Monday and Tuesday with a 20-40% chance for temperatures exceeding 100 degrees F from Salem to Portland-Vancouver on Monday, increasing to 40-60% on Tuesday. Overnight lows will also be warm, especially across the central Willamette Valley, Columbia Gorge, and Portland- Vancouver Metro Area where there is a 40-60% chance for Tuesday and Wednesday morning lows to remain above 65 degrees (highest chances across Portland-Vancouver Metro due to urban heat islands effects). Overnight lows near or above 65 degrees would provide limited overnight relief from the heat. As a result, there will be widespread Moderate HeatRisk across much of northwest Oregon and southwest Washington during this period, with localized Major HeatRisk across the Portland-Vancvouer Metro Area through the Columbia Gorge from the warm overnight temperatures. This has prompted the issuance of an Extreme Heat Watch for these two areas starting Monday morning and continuing through Tuesday evening. Make sure to practice heat safety, including staying hydrated, wearing light-colored and loose- fitted clothing, wearing sun protection, and taking frequent breaks from the heat. If possible, schedule outdoor plans during the early morning or late evening when temperatures will be less intense.

Elevated forecast uncertainty remains on Wednesday although ensemble guidance on the whole (AI and numerical) has slowly been trending warmer run to run. As of the 12z model runs today, around ~65% of the numerical ensemble space keep upper-level ridging overhead for one more day thus maintain hot temperatures well into the 90s, while the other ~35% of ensembles shift the axis of the ridge to our east ushering in the return of weak onshore flow and "cooler" temperatures (80s to near 90). Still, within the latest NBM there is currently a 17-20 degree spread between the NBM 10th and 90th percentiles on Wednesday for the Willamette Valley and Portland Metro, with the coolest scenario being in the mid 80s while the warmest scenario pushes highs near 100 degrees F. Should the warming trend on Wednesday continue, heat related impacts may extend yet another day. At least there is more agreement among guidance for the ridge axis to nudge eastward by Thursday and Friday allowing temperatures to decrease further, albeit still above normal for June. -99

AVIATION

Onshore flow through the next 24 hours will lead to widespread stratus with a marine push along the coast. Overall looking at MVFR to IFR CIGs along the coast with increasing chances for MVFR conditions through the Cascade foothills and just east of I-5. Backbuilding off of the Cascades would drive the inland stratus. Along the coast, some high resolution models are suggesting high probabilities of IFR CIGs, however, with the persistent cloud cover from the day, we will need more significant cooling or stronger onshore flow than what is occurring at this time. Conditions will improve after 18Z Sat, but the coast may hold onto those lower CIG conditions longer.

After 00Z Sun, another surge of marine stratus will filter into the coast bringing even more MVFR and potentially IFR CIGs to the region.

KPDX AND APPROACHES...VFR with westerly flow. After 10Z Sat, high resolution models are suggesting a backbuilding of marine stratus off of the Cascades. There is around a 50% chance of MVFR CIGs by 12Z Sat which eases by 18Z Sat as skies begin to clear with drier air moving into the area. -27

MARINE

High pressure offshore continues to maintain northerly to northwesterly winds over the next seven days. A Small Craft Advisory remains in effect across the outer waters (beyond 10 NM offshore) through 11 PM Saturday. Tonight, there will be breezy northwesterly winds with gusts up to 25 kt, then winds weaken into Saturday morning as the pressure gradient eases. Steep and choppy seas will continue until late Saturday, around 8 to 11 ft at 9 to 10 seconds. Seas subside to 5 to 7 ft Saturday into Sunday. Seas remain around 6 to 8 ft or less into early next week. -12

PQR WATCHES/WARNINGS/ADVISORIES

OR...Extreme Heat Watch from Monday morning through Tuesday evening for ORZ109-111-112-120-122. WA...Extreme Heat Watch from Monday morning through Tuesday evening for WAZ206-207-209-210. PZ...Small Craft Advisory until 5 PM PDT Saturday for PZZ271>273.