textproduct: Seattle/Tacoma

SYNOPSIS

Upper level ridge offshore extending into the British Columbia coastline today will sag south over Western Washington Monday and Tuesday. The ridge will remain over the area through Thursday then shift east Friday. A dissipating front will arrive Friday night and Saturday. In the lower levels offshore flow today will weaken tonight and become onshore Monday. Varying degrees of onshore flow for the remainder of the week.

SHORT TERM /TODAY THROUGH TUESDAY/

Satellite imagery shows clear skies over Western Washington early this morning. Temperatures at 3 am/10z range from the mid 40s to the mid 50s except in areas with exposure to the east winds. These locations are still in the lower 60s. There is a chance some record high minimum temperatures could be set today.

Low level offshore flow kicking it in gear this morning. Winds at Snoqualmie Pass turned easterly late last night. Winds at observation sites in the Olympics, which turned easterly yesterday, are increasing with multiple sites reporting peak winds near 15 mph. Seattle-Tacoma airport and Paine Field in Everett still 60 degrees. These easterly winds will mix down to the surface this morning and continue through the afternoon hours. Record breaking highs today in the mid 70s to mid 80s. Current records, Seattle 77 degrees (1992) forecast high 83, Olympia 80 degrees (1992) forecast high 86, Quillayute 83 (1992) forecast high 84. Olympia to Bellingham gradient down to around -2 mb in the afternoon. Locations near the Sound will get a cooling afternoon seabreeze keeping highs in the mid 70s.

Low level flow going flat overnight into Monday morning. Mild low temperatures Monday morning, in the upper 40s to mid 50s.

Monday a transition day with the low level flow going onshore. Temperatures cooling way down along the coast with highs in the mid 60s. High temperatures for the interior a little trickier. By 00z Tuesday KOTH-KSEA gradient around plus 5 mb, KUIL-KBLI around plus 3 mb and KHQM-KSEA around plus 3 mb. The KOLM-KBLI gradient is flat. The air mass over the interior will still be warm making it hard for the marine layer to make much of a dent in the afternoon. Temperatures aloft do cool slightly, 850 mb temperatures going from plus 16C to around plus 14C. For now will go with some slight cooling, up to 5 degrees, for the interior putting highs in the 70s to lower 80s.

Low level onshore flow peaking Monday night with the marine layer getting into the interior by Tuesday morning. Lows in the mid 40s to mid 50s.

Upper level ridge, currently along the British Columbia coastline, will be over the top of Western Washington Tuesday. Stratus getting east of Puget Sound in the morning but with the low level onshore flow going flat in the afternoon do not expect the stratus to be around except along the coastline in the afternoon. A little more cooling for the interior with highs in the upper 60s to mid 70s. Highs along the coast in the lower 60s.

In Seattle the normal number of days with highs 80 plus in May is 2. The record for the month is 7 in 1958. In 81 years of records at Seattle-Tacoma airport there have been 21 years ( 26% of the time ) without an 80 degree plus day in May. The last year without an 80 degree plus day in May in Seattle was 2022. Out of the 145 days in May with a high 80 degrees plus only 13 of them ( 9% ) have occurred in the first week. The last time there was an 80 degree plus day in the first week of May, May 7, 2016 ( 82 degrees ). Felton

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Extended models showing good consistency this morning. Upper level ridge will vary in strength over Western Washington into Thursday with varying degrees of low level onshore flow as well. The ridge shifts east Friday. Dissipating front arriving Friday night or Saturday bringing slight chance pops to the area. Highs remaining above normal for the interior through Thursday, in the mid 60s to lower 70s. Highs lowering back into the 60s Friday and Saturday. Onshore flow will keep highs in the lower 60s along the coast.

AVIATION

North to northeast flow aloft continues with an upper ridge centered offshore. The low level flow is weakly offshore. The air mass is dry and stable with VFR expected areawide today. A shallow marine layer will return to coastal areas after 09Z Monday as low level onshore flow returns.

KSEA...VFR. Surface winds N/NE 4 to 7 knots rising to 7 to 10 knots this afternoon.

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MARINE

Thermally induced low pressure will lead to weak northerly or offshore flow today. The thermal trough will shift inland on Monday for a return to onshore flow that will persist into the week ahead as a surface ridge remains anchored offshore.

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HYDROLOGY

No river flooding in the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.