textproduct: Portland

SYNOPSIS

Over the next 5 to 7 days we'll get to experience a bit of everything weather-wise as we go from hot/dry to cooler and wet. The hottest days of the week are expected on Monday and Tuesday with inland high temperatures punching into the 90s accompanied by widespread Moderate to near Major HeatRisk values. A Heat Advisory is in effect for the inland valleys Salem northward through the Portland Metro/SW Washington including the Columbia River Gorge. Fairly warm overnight temperatures may provide a limited window of overnight relief in our urban centers. Temperatures begin to slowly trend cooler Wednesday with moderate to high confidence in a cool and wetter pattern (by June standards) taking hold to end the week.

DISCUSSION...Today through Saturday

Skies have completely cleared this afternoon thanks to a ridge of high pressure amplifying just off the coastline. This ridge feature will help facilitate a period of abnormally warm conditions to start the work week as it progresses overhead with the majority of guidance pointing to high temperatures exceeding 90F across the inland valleys of southwest Washington and western Oregon Monday and Tuesday. However, compared to yesterday, NBM model guidance has decreased projected high temperatures by ~1-4 degrees across the inland valleys areas while also nudging overnight minimum temperatures a touch lower as well. This correction may be due to the NBM finally being within the time period to ingest shorter-range high resolution guidance, and/or better ensemble agreement on the eastward placement of the surface thermal trough axis. Nonetheless, heat related impacts may still be felt from the Central Willamette Valley through the Portland Metro, Columbia River Gorge, and the southwest Washington lowlands where a Heat Advisory is in effect through Tuesday evening.

For those hoping to see us rise into the triple digits Mon/Tue those chances are waning but still worth pointing out as the NBM maintains a 10-30% chance for the central/south Portland metro to meet or exceed 100F Tuesday afternoon. We'll see how these probabilities evolve come tonight/tomorrow's forecast although they'll likely continue to drop given the latest trends and overall set-up not appearing conducive for 100+ degree temperatures as we maintain weak NNW flow on Tuesday. If you're a glutton for truly hot conditions you'd want a much stronger easterly component of the low-level flow (surface-850mb), the surface thermal trough axis placed along the coastline or just offshore, and a stronger ridge of high pressure overhead - in this case it's weakening temporally. That said, temperatures are still expected to be 15-20 degrees above normal even without the aforementioned variables aligning. Make sure to stay 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.

Then on Wednesday the vast majority of ensemble members kick the broader upper-level ridge axis east of the Cascade crest- line during the daytime hours. This should allow for high temperatures to drop a few degrees into the upper 80s to low 90s across the interior lowlands although the greatest day the day temperature change will likely be felt along the coast and in the some of the coast range valleys as westerly flow begins to increase in earnest. The latest NBM still gives a 20-50% chance for highs to exceed 95 degrees Wednesday afternoon from Salem to the Portland- Vancouver Metro - something to watch. At least confidence is very high temperatures begin a noticeable descent back to normal, then below normal, the remainder of the week as the upper-level pattern undergoes a significant shift.

Thursday through the start of the weekend the majority of deterministic and ensemble guidance are depicting a upper-level trough of low pressure moving into the Pacific Northwest ushering in a cooler and wetter pattern. There still remains some uncertainty with the exact timing, placement, and magnitude of the trough, and thus there is uncertainty regarding exact precipitation amounts. The latest ensembles, including the NBM, are highlighting late Thursday night into Friday morning as best chance (60-95%) for rainfall during this late week period, mainly focused along the coast, coast range, Portland Metro through SW Washington, and in the Cascades. Should the core of the upper-level trough/low track overhead Friday and Saturday, post-frontal thunderstorms are another concern we'll have to watch. At the end of the day, any precipitation be can get this time of year is largely beneficial and we'll take what we can get during this late week/early weekend period. -99

AVIATION

Satellite and surface weather observations from 0530Z Monday showed low marine stratus beginning to fill in along the coast with ceilings around 700-800 ft. Expect this stratus deck to linger through tonight at the coast, before scattering out and pushing back offshore around 17-18Z Monday. However, there is a 30-40% chance low clouds will fail to clear out at KONP on Monday.

Meanwhile, inland areas will remain clear with VFR conditions. Light winds tonight will increase out of the north late Monday morning into Monday afternoon to 7-11 kt. Winds may occasionally gusts as high as 15-18 kt between 22Z Monday and 03Z Tuesday, except up to 20 kt at KONP.

KPDX AND APPROACHES...Clear skies will maintain VFR conditions through 06Z Tuesday. Northwest winds around 7 kt this evening should become light and variable around 08Z Tuesday. Winds increase out of the north after 20Z Monday with gusts up to around 15-17 kt by late Monday afternoon. -23

MARINE

Northwesterly winds will generally stay under 20 kt through Monday morning, aside from occasional small craft advisory wind gusts up to 21 kt over the outer waters. Seas will remain steep and choppy around 5-7 ft in the outer waters through at least Tuesday morning. High pressure re-builds Monday afternoon into Tuesday, tightening pressure gradients and increasing north-northwesterly winds with gusts up to 25 kt. Small Craft Advisories are in effect for the outer waters (beyond 10 NM offshore) until 5 AM Tuesday for the waters south of Cape Falcon. For the outer waters north of Cape Falcon, the Small Craft Advisory is in effect until 5 AM Monday. Expect seas of 5 to 7 ft through most of this upcoming work week. There is only a 10-20% chance for seas exceeding 7 feet at any given hour from Monday to Wednesday. -23/10

PQR WATCHES/WARNINGS/ADVISORIES

OR...Heat Advisory from 11 AM Monday to 11 PM PDT Tuesday for ORZ108>115-119>123.

WA...Heat Advisory from 11 AM Monday to 11 PM PDT Tuesday for WAZ204>210.

PZ...Small Craft Advisory until 5 AM PDT Monday for PZZ271.

Small Craft Advisory until 5 AM PDT Tuesday for PZZ272-273.