textproduct: Seattle/Tacoma

SYNOPSIS

Upper level ridge offshore moving east over Western Washington Saturday. The ridge will remain in place through Monday then weaken through the middle of next week. Low level onshore flow today will become light Saturday. Low level flow turning offshore Saturday night with thermally induced surface trough along the coast. Thermal trough shifting inland Monday and east of the Cascades Monday night. Low level onshore flow increasing Tuesday into Wednesday with a cooling trend. Temperatures peaking Sunday and Monday with record highs likely.

SHORT TERM /TODAY THROUGH SUNDAY/

Satellite imagery shows a little bit of stratus along the north coast, near Grays Harbor and in the North and Central Cascades. Mostly clear skies over the remainder of the area. Temperatures at 3 am/10z were in the upper 40s to mid 50s.

Upper level ridge building well offshore today with the ridge axis near 135W. Surface high pressure also centered well offshore with northwesterly onshore surface gradients. Sunny skies across the area with what little stratus there is out there not lasting very long. Highs in the upper 60s and 70s.

Upper level ridge offshore moving east tonight and Saturday with the ridge axis inside 130W Saturday afternoon. Temperatures aloft warming. Thermally induced surface trough moving up the Oregon coast during the day with weakening northwesterly onshore gradients. Under mostly clear skies high temperatures warming into the upper 70s and 80s. Lows tonight upper 40s to mid 50s.

Thermally induced surface trough moving up the Washington coast Saturday night and remaining along the coast through Sunday. Upper level ridge axis moving over Western Washington. Temperatures aloft continuing to warm. This combined with the low level offshore flow will produce record high temperatures in many locations Sunday. Highs in the 80s common with lower 90s in the warmer locations like the Southwest Interior.

A heat advisory will go into effect beginning at 11 am/18z Sunday with widespread moderate HeatRisk across the area and a slight chance of major HeatRisk over the Southwest Interior and Lower Chehalis Valley. Felton

LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/

Models consistent with high temperatures peaking Monday as the thermally induced surface trough moves inland. The exception to this will be the coast where afternoon seabreezes will cap highs in the 70s. For the interior highs in the 80s to mid 90s.

Warm night Monday night over the interior with the thermally induced trough in the area. Lows in the Seattle metro area will be above 60 degrees with other inland locations near 60. The heat advisory will remain in effect through 5 am/12z Tuesday morning.

Upper level ridge weakening Tuesday. Onshore flow in the lower levels kicking in with the thermally induced surface trough east of the Cascades. High confidence that Tuesday will be cooler. How much cooler is another story. Models have been oscillating between a weaker marine push, high temperatures dropping 5 degrees or so, versus a stronger push that would drop high temperatures 10 to 15 degrees. Models now leaning towards the stronger push scenario. Model surface progs showing the surface ridge axis to the south. This is a good indicator of a stronger push. Will go with that idea for this forecast package putting highs in the 70s for the interior and mid 60s for the coast.

Upper level ridge continuing to slowly weaken Wednesday and Thursday. 500 mb heights still near 580 dms Thursday afternoon. Increasing low level onshore flow will deepen the marine layer over the interior cooling highs a few more degrees but at this point the marine layer does not look deep enough to stick around in the afternoon. Highs Wednesday and Thursday near normal, upper 60s to mid 70s inland and mid 60s along the coast. Felton

AVIATION

VFR conditions across all terminals early this morning. Probabilities for MVFR cigs along the coast have decreased with the latest guidance, now with a 30-50% chance. There is also a slight chance (25%) for IFR cigs. The timing for these lower cigs still remains the same, between 12z-18z, before clouds scatter out to VFR. Light to calm northerly winds overnight across the majority of the terminals. North winds increase in the afternoon to 5-12 kt.

KSEA...VFR conditions will prevail today. NE winds early this morning remaining slightly elevated at 5-8 kt, but should decrease after 12z to 5 kt or less. Winds will then shift N/NW Friday afternoon at speeds of 5-10 kt after 16z.

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MARINE

Broad high pressure continues to build over the NE Pacific and will also start to also settle over area waters today. High pressure is expected to strengthen over the waters this weekend through Monday establishing northerly flow over the waters. On Tuesday, high pressure will then weaken over the region as the broad area of high pressure retreats back into the open waters of the Pacific in the wake of an incoming frontal system. Onshore flow also returns Tuesday. There is increasing confidence (70% chance or greater) for gales through the Strait of Juan de Fuca on Tuesday. Seas will also build on Tuesday, with guidance suggesting seas building above 10 feet.

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FIRE WEATHER

Drying trend over the area the next few days with elevated fire weather concerns beginning Saturday and lasting into Tuesday. Upper level ridge building this weekend with the low level flow turning offshore Saturday night. Highs warming into the 80s Saturday, 80s to lower 90s Sunday and for the interior 80s to mid 90s Monday. Relative humidity values lowering in the drier locations, like the 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. Winds will become particularly gusty, with portions of the coast/mountains/south interior seeing west to northwest wind gusts up to 20 to 30 mph. Low level onshore flow and cooler temperatures Wednesday and Thursday will ease fire weather concerns the middle of next week. Felton/HPR

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.