textproduct: Seattle/Tacoma

SYNOPSIS

A warming and drying trend will continue across western Washington through the middle of the week, with temperatures reaching the low 90s for many lowland areas Tuesday and Wednesday. Onshore flow will increase during the latter half of the week, bringing cooler temperatures with chances for showers and morning low clouds.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

An upper level ridge will continue to build over the Great Basin through the middle of the week, with a low pressure system situated offshore. This will maintain southerly flow aloft over western Washington, pulling in warmer air through Wednesday. Temperatures today are on track to peak well into the 80s across much of the lowlands, with further warming bringing temperatures closer to 90 degrees on Tuesday. By Wednesday, many areas east and south of the Puget Sound will see high temperatures peaking in the low to mid 90s, which may result in the warmest day of the year so far. This will also correspond to widespread areas of both Moderate (Orange) and Major (Red) HeatRisk on Tuesday and Wednesday, which reflects an increased risk of heat-related illness to those without access to cooling or hydration. A Heat Advisory remains in effect for all inland lowland areas from Tuesday morning to Wednesday evening.

In addition to the heat, northerly flow at times will pull wildfire smoke from British Columbia into Whatcom and Skagit Counties, and an Air Quality Alert has been issued by the Northwest Clean Air Agency. Weak easterly flow tonight into Tuesday will also bring wildfire smoke from eastern Washington west of the crest tonight into Tuesday. While incoming wildfire smoke may cause localized degradations in air quality at times over the mountains, the smoke is not expected to mix down into the lower levels and is favored to stay east of the Seattle metro.

LONG TERM /THURSDAY THROUGH MONDAY/

The remnants of tropical storm Elida will meander northward late Wednesday into Thursday, and while confidence is low, this may produce isolated thunderstorms over higher elevations. Increased onshore flow by Friday will bring in more seasonable temperatures in the upper 70s to the region, with a return to morning low clouds and afternoon sunbreaks. Models struggle to come into agreement over the potential for any incoming showers in the long term, with ensembles maintaining chances for showers over the northern Olympic Peninsula and northern interior through the weekend and into early next week.

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AVIATION

Strong high pressure building over the region with dry conditions in place. With light northerly flow over the region in the lower levels, expect VFR conditions under variable high cirrus and some entrained smoke overhead through the period. Winds increase a bit through the evening, before going light or calm overnight. LIFR stratus will return along the immediate coastline tonight before clearing out Tuesday morning. Northerly surface winds again increase Tuesday through much of the region. Increasing wildfire smoke across northwest WA may begin to limit both horizontal and slant-range visibility by this afternoon.

KSEA...West/northwest surface winds this afternoon will ease overnight, before increasing again Tuesday afternoon. VFR conditions continue with high clouds and occasional smoke aloft, but ceilings and reductions in visibility at the surface are not expected through the period.

MARINE

High pressure will remain situated inland as a low pressure system stalls over the offshore waters, maintaining northwesterly flow over the outer waters through the first half of the week. Stronger onshore flow will resume by late Thursday, bringing potential for Small Craft westerly pushes through the Strait of Juan de Fuca daily thereafter heading into the weekend.

Seas will generally remain between 5 to 7 feet through the week.

FIRE WEATHER

Elevated fire weather concerns will continue through Wednesday due to very warm and dry conditions. Minimum relative humidities will fall as low as 20% to 30% on Tuesday and Wednesday, with drier locations across the southern Puget Sound potentially bottoming out in the teens. In addition, a thermal trough will build along the coast today and will shift inland during the daytime hours and back along the coast overnight each day through Wednesday. While a large degree of uncertainty remains over the track of incoming showers and thunderstorms, the potential for storms coming in from the south late Wednesday into Thursday pose a risk of elevated fire weather conditions, as additional ignitions from lightning cannot be ruled out. Onshore flow will increase by Friday, bringing cooler temperatures and better overnight RH recoveries through the weekend.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Air Quality Alert until 9 AM PDT Wednesday for Cascades of Whatcom and Skagit Counties-Foothills and Valleys of the North Cascades-Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County.

Heat Advisory from 10 AM Tuesday to 11 PM PDT Wednesday for City of Seattle-Downtown Everett / Marysville Area- Eastern Kitsap County-Eastern Strait of Juan de Fuca- Eastside-Foothills and Valleys of Central King County- Foothills and Valleys of Pierce and Southern King Counties-Foothills and Valleys of Snohomish and Northern King Counties-Foothills and Valleys of Thurston and Lewis Counties-Foothills and Valleys of the North Cascades- Foothills of the Western and Southern Olympic Peninsula- Lake Crescent Area Including US 101-Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-Middle Chehalis River Valley-Northern Hood Canal-Olympia and Southern Puget Sound-Port Townsend Area- Shoreline / Lynnwood / South Everett Area-Southern Hood Canal.

PZ...None.