textproduct: Seattle/Tacoma

SYNOPSIS

A dry and warm airmass associated with a strong upper level ridge will settle over Western Washington this weekend through Monday. Temperatures peaking in the 80s and 90s will bring widespread Moderate HeatRisk to the region on Sunday and Monday. Offshore flow will bring lower relative humidities and elevated fire danger. The ridge will weaken on Tuesday, resulting in increased onshore flow and cooler temperatures through the rest of the week.

SHORT TERM /TODAY THROUGH MONDAY/

An upper level ridge will maintain a dry and very warm airmass over Western Washington through Monday. Currently the upper level ridge axis sits over British Columbia. Latest satellite imagery has Washington under clear skies with temperatures in the mid to upper 50s. A sunny day is in store today across the region. High temperatures will reach the upper 70s to 80s. The ridge axis will move inland on Sunday and remain situated over the region through Monday. The forecast remains on track with Sunday and Monday being the hottest days as a thermal trough settles over the region. Temperatures are expected to peak into the mid 80s to 90s. As a result, widespread Moderate HeatRisk is expected across the region. In addition to warm daytime temperatures, little overnight relief is expected as low temperatures will only decrease into the upper 50s to low 60s.

Breezy northerly winds are expected across Puget Sound this afternoon/evening with gusts reaching 15-20 mph, with periods of offshore flow across the foothills and Cascades. Offshore flow will increase late Saturday night/Sunday morning across the southern Cascades and foothills, with gusts 15-20 mph funneling through the gaps. Another round of breezy winds expected Sunday afternoon across Puget Sound.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Overnight temperatures Monday night into Tuesday morning will be on the warm side as well, with low temperatures in the upper 50s to low 60s. The upper level ridge will begin to flatten late Monday night. Long term guidance suggests a zonal pattern is favored to develop over Western Washington, promoting an onshore flow and cooler temperatures with highs in the 60s along the coast and upper 70s to low 80s in the interior through the rest of the week.

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AVIATION

Dry conditions and VFR ceilings prevail through the TAF forecast period due to high pressure centered offshore. Expect light northerly winds around 5 kts this morning, increasing to around 10 kts during peak diurnal heating this afternoon and evening. Gusts to 15 kts possible, especially in and around the Seattle metro area.

KSEA...Clear skies. Surface northerly winds of 6 to 8 knots this morning will rise to northerly 8 to 12 knots this afternoon. Gusts to 16 kts possible.

MARINE

Expansive surface high pressure centered offshore will persist through early next week. A thermal trough will build over Western Oregon and shift into the interior of Western Washington starting Sunday night. This will induce onshore flow for the interior coastal waters starting Sunday night into Monday. Additional pushes likely occur for the Straight of Juan de Fuca Monday through Wednesday, with potential for gales.

Coastal seas will remain well under 10 feet through the weekend before building to around 10 feet by late Tuesday. Higher swells to around 13 ft possible Wednesday.

FIRE WEATHER

A dry and warm trend over the next few days with elevated fire weather concerns through Tuesday. An upper level ridge over the area this weekend with low level flow turning offshore Saturday night. Daytime temps will warm into the 80s Saturday and 80s to 90s Sunday and Monday. Relative humidity values will lower in the drier locations, like Southwest Interior, into the teens both Sunday and Monday afternoon. Even though fine fuels have not reached critical thresholds, this rapid drying will create elevated fire concerns especially for dry grassy/shrubby areas, as well as piles of dead fuels. Offshore flow Sunday into Monday will prevent good relative humidity recoveries overnight. Relative humidities will improve with the return of onshore flow Tuesday. Low level onshore flow and cooler temperatures throughout the week will ease fire weather concerns.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Heat Advisory from 11 AM Sunday to 5 AM PDT Tuesday 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- Island County-Lake Crescent Area Including US 101-Lower Chehalis River Valley-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-San Juan County-Shoreline / Lynnwood / South Everett Area-Southern Hood Canal-Willapa and Black Hills.

PZ...None.