textproduct: Seattle/Tacoma

SYNOPSIS

Upper level ridging building into the region will lend itself to much above normal temperatures throughout the first half of the week. Dry conditions are expected to accompany the heat for elevated fire weather concerns. The ridge will weaken in the second half of the week as low pressure moves up from the south and may reintroduce chances for thunderstorms in the forecast for later this week.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

Mostly clear this afternoon with some scattered clouds over the terrain. The warmup will begin in earnest through the middle of the week as temperatures climb into the upper 80s and low 90s throughout much of the lowland locations. As such, a heat advisory has been issued beginning on Tuesday and lasting into late Wednesday night. Expect widespread Moderate HeatRisk levels on Monday, increasing to Major for the urban heat islands and areas of the south Puget Sound on Tuesday. Warming overnight lows on Tuesday and Wednesday morning contributed to the bump in HeatRisk levels. Overnight lows are expected to be as warm as 60 to 65 degrees for many locations, meaning that adequate relief from the heat of the day may not be fully realized, especially for those who are sensitive to the heat or lack cooling.

Temperatures in far northwestern Washington, including the Bellingham and San Juan county area, may be subject to being a few degrees cooler due to smoke coming in tomorrow from active fires in British Columbia. As the flow goes northerly, smoke gets into the Fraser river valley and exits in and around the Bellingham area. A more noticeable haze may be present in these areas tomorrow. Please refer to your local clean air agency for information on the air quality readings and forecast.

As the ridge continues to amplify, temperatures reach the upper 80s to low 90s on Tuesday, whilst continuing to be very dry.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

The aforementioned Heat Advisory will remain in effect through late Wednesday night as temperatures remain in the low 90s. While temperatures will be decreasing through the end of the week, there is still considerable uncertainty as to the fate of the remnant tropical moisture from Elida or possible monsoonal moisture re-entering the northwest.

Specifics aren't in focus yet, though the ensemble cluster analysis shows signals for a trough coming up the west coast, but in various positions which does have a bearing on what to expect west of the Cascade crest. Some model solutions show the low spinning up some showers in the area come Thursday morning. Thunderstorm chances are low at this time, but cannot be fully ruled out for Thursday and Friday. With the solution possibly being a low pressure system traversing the region late in the week, the resumption of onshore flow can be expected, cooling things off by up to 10 degrees from the peak heat of the week.

Temperatures as of now for the weekend are forecast to be in the mid 70s.

AVIATION

Stratus has now retreated to the immediate coastline, and will remain like so through the remainder of the day for VFR conditions today. Stratus looks to redevelop tonight along the coast, but remain west of the inland terminals. VFR conditions look to otherwise continue tomorrow with high clouds overhead. Increasing smoke across northwest WA on Monday may begin to limit both horizontal and slant-range visibility by Monday afternoon. N/NW winds 5 to 10 kt become 5 kt or less overnight and remain light into Monday.

KSEA...VFR conditions prevail through the TAF period. NW winds 5 to 10 kt becoming NE 5 kt or less overnight. N winds continue tomorrow.

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MARINE

High pressure will remain centered offshore with lower pressure inland through the week. Breezy northwest winds will continue over the coastal waters today and tonight, making for steep 6 to 8 ft seas. Winds and seas are on track to ease early Monday morning. Onshore gradients will ease through the early part of the week as thermally-induced low pressure develops across Western Washington and Oregon. Stronger onshore flow and pushes down the Strait look to resume in the latter half of the week as the thermal trough shifts eastward. There is more uncertainty in the pattern in the long term, with the potential for disturbances to move across the area late week into next weekend. 62

FIRE WEATHER

The building ridge will come with very dry conditions. Minimum relative humidity values are expected to be in the 20 to 30 percent range, with drier locations in the south Sound capable of getting into the upper teens. Elevated fire weather conditions are going to be in place through the middle of the week. While there is still a lot of uncertainty regarding the low pressure system off the coast from what was once tropical storm Elida, chances for thunderstorms late in the week are low at this point, but cannot be fully ruled out. Any thunderstorms that develop after another round of hot and very dry conditions pose a risk of additional ignitions from lightning.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...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...Small Craft Advisory until 5 AM PDT Monday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm- Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.