textproduct: Seattle/Tacoma

UPDATE

Scattered showers and thunderstorms making their way northeastward over western Washington this evening. Activity has had some difficulty holding together as it moves into the area with the most impressive cells winnowing away as they enter the CWA. However, still getting strikes on satellite and while thunder risk may diminish further tonight and overnight, cannot rule out isolated thunderstorms into Thursday. Otherwise, inherited forecast remains on track. 18

SYNOPSIS

Moisture working its way up into the area from the south will result in chances for showers and isolated thunderstorms into Thursday. An upper level trough offshore will then push inland over the weekend, bringing cooler temperatures to the area and additional chances of showers. Troughing will persist through early next week, allowing for temperatures to trend just below to near normal.

SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/

It's hot out there- latest observations show temperatures trending in the mid 80s to mid 90s across much of the interior of western Washington this afternoon. The thermal trough that was situated along the coast has started to make its way inland as winds have already switched back to onshore this afternoon. Temperatures along the Pacific coast are currently trending in the mid 50s to mid 60s as a result and shower activity and cloud cover have started to stream up into the area. Chances of showers and isolated thunderstorm activity will increase this evening along the coast, areas south of the Sound, and the southern Cascades as moisture from a trough offshore continues to stream northward into the area. With dry conditions in the low levels, any rainfall associated with the shower activity that initially moves into the area may have a hard time making it all the way to the ground. Shower and isolated thunderstorm activity will then increase in coverage and expand area wide tonight into the overnight period as moisture continues to stream into the region and winds transition to southwesterly. Critical fire weather conditions are expected to develop along the coast, south interior, and southern Cascades tonight into Thursday as lightning from isolated thunderstorm activity could cause additional ignitions.

Thursday morning low temperatures will remain mild and will generally be in the upper 50s to mid 60s across the area. Shower and thunderstorm chances will continue through the day on Thursday, but will gradually become more confined to the Cascades. The pattern change will allow for afternoon high temperatures to cool 10 to 15 degrees in comparison to today, with highs expected to top out in the upper 70s to low 80s across the area.

Drier conditions and a slight warm up are expected again by Friday with an upper level trough remaining offshore. Onshore flow will allow for the marine stratus to push into the Sound by early Friday morning and will bring cooler morning lows to the area- mostly in the 50s to low 60s. The layer will retreat back to the coast by the afternoon, allowing for highs across the interior to warm back into the mid 80s. Highs along the coast will remain cooler under the marine stratus- and only look to top out in the mid 60s to low 70s.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Guidance remains in good agreement that the upper level trough offshore will move across the area over the weekend, which will bring cooler temperatures and additional chances of showers to western Washington. The greatest chances of precipitation will be along the coast and northern interior areas on Sunday as a shortwave from a trough off the coast of British Columbia moves into the area. Afternoon high temperatures will be below to near normal across the area as a result and are expected to be in the upper 60s to mid 70s across the interior and in the 60s along the coast. Upper level troughing then looks to remain the dominant influence across the region heading into early next week. This will help promote continued onshore flow across the area and high temperatures in the 70s through Wednesday.

AVIATION

High pressure with a ridge will move to the north as a shortwave trough to the south with an associated upper low will move north tonight into Thursday, with increasing flow from the south aloft. Main concern this evening remains thunder as activity tracks up along the I-5 corridor this evening. Coverage continues to remain in clusters/pockets of convection, with movement to the north around 20- 30 kt. The main hazards remain lightning with gusty winds, although precipitation output has been limited overall. Activity will move to the northeast overnight into the Cascades, with thunder chances Thursday remaining primarily in the Olympics/northwest coast. Ceilings will also lower tonight/Thursday morning, with a 50-60% chance of MVFR for most interior terminals Thursday morning (12Z- 21Z), with higher chances of IFR ceilings/visibilities along the coast. Northwest winds 8-12 kt will switch to the southwest tonight into Thursday 5-10 kt.

KSEA...VFR skies through the evening. Convection to arrive at the terminal 03Z, and linger through at least 06Z (though a couple ensemble members have convection lingering an hour or two after as storms to the southwest shift to the northeast). After the thunder moves out, there is a 50-60% chance of MVFR ceilings developing from 12Z to as late as 21Z. Thunder potential for Thursday remains less than 10%. West-northwest winds at 10 kt will switch to the southwest as the convection moves through.

HPR

MARINE

The thermal trough will continue to shift inland, ushering stronger onshore flow back into the region. Expect westerly winds to increase to 25 kt through the central and eastern Strait of Juan de Fuca tonight. Given higher confidence in increasing southerly winds around Bellingham Bay and also through the southern half of Puget Sound, have also issued small craft advisories for the two additional zones for tonight. With onshore flow containing into the weekend, expect to see additional SCA strength winds through the Strait later this week. Seas over the coastal waters remain generally around 5 to 6 ft, but may build further on Saturday (especially over the southern coastal zones) as a result of stronger southerly winds with a persistent fetch through the inner coastal waters. Cullen

FIRE WEATHER

Elevated fire weather concerns continue today through Thursday resulting from multiple causes. Today is seeing hot and dry conditions. Minimum relative humidities will fall as low as 20% to 30% again later this afternoon, with the drier locations across the southern Puget Sound and portions of the Cascades and Olympics. There is a chance of thunderstorms coming in from the south late Wednesday night through Thursday with the arrival of the remnants of tropical storm Elida, which, given the warm and dry conditions, could cause additional ignitions from lightning. Rainfall from these storms will mainly be light. A Red Flag Warning was issued for the southern Cascades, South Sound, and Olympic Peninsula areas tonight through Thursday night.

Increasing onshore flow beginning later Thursday will bring a wind shift with breezy southwest winds. This will also produce cooler temperatures and better overnight RH recoveries through the weekend into the first part of next week easing fire weather concerns. FELTON/JBB

SEW WATCHES/WARNINGS/ADVISORIES

WA...Red Flag Warning until 10 PM PDT Thursday for Black Hills and Southwest Interior Lowlands-Central Coastal Lowlands-East Portion of the Olympic Mountains-North Coastal Lowlands- North and Central Coastal Strip-West Portion of the Olympic Mountains-West Slopes of the Central Cascades Generally above 1500 Feet.

Heat Advisory until 11 PM PDT this evening 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 from 8 PM this evening to 5 AM PDT Thursday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from midnight tonight to 9 AM PDT Thursday for Northern Inland Waters Including The San Juan Islands.

Small Craft Advisory until 9 AM PDT Thursday for Puget Sound and Hood Canal.