textproduct: Seattle/Tacoma

UPDATE

No changes made in this evening's update. The previous discussion remains below along with an updated aviation section:

SYNOPSIS

Zonal flow aloft and onshore flow will maintain seasonable conditions with morning clouds and afternoon sunshine through Tuesday. An upper level trough will dig into the region Wednesday, bringing cooler temperatures alongside showers and thunderstorms over the North Cascades Wednesday and Thursday. Warmer conditions will return by the weekend as upper ridging rebuilds over the region.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

The overall weather pattern will continue to remain consistent into Tuesday as zonal flow aloft continues. Stratus has burned off this afternoon for most inland areas, revealing plentiful sunshine with near-normal temperatures. Highs today across the lowlands will peak in the mid to upper 70s, with highs in the upper 60s along the coast. Another round of marine stratus will expand inland overnight tonight, bringing cloudy conditions once again Tuesday morning. The stratus layer will burn off by the afternoon, revealing very similar conditions to today.

An upper level trough will move southward over British Columbia and cross western Washington on Wednesday, bringing showers and a chance of thunderstorms to the Olympics and North Cascades. This cooler air mass will also lower temperatures several degrees across the region, falling a couple degrees short of seasonal normals.

LONG TERM /THURSDAY THROUGH MONDAY/

The aforementioned upper trough will remain overhead on Thursday with a weak shortwave rippling through. This will likely maintain showers and isolated thunderstorm activity over higher terrain, extending further southward across the western Washington Cascades.

A warming trend is set to begin by the end of the work week as weak ridging builds over the area, with high temperatures warming into the low to mid 80s across the lowlands by Friday. Saturday will bring more of the same, resulting in areas of Moderate (orange) HeatRisk across the Puget Sound metro areas. However, this will be short lived as ensembles show a slight cool- down back to normal heading into next week.

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AVIATION

Westerly flow continues aloft with onshore flow in the low levels. Stratus is expected to spread inland again tonight as it's currently over the coast (Grays Harbor northward towards KUIL), but areal coverage may be somewhat less with an earlier burn off on Tuesday. Areas of IFR ceilings are expected across the interior again from 12Z to 19Z before retreating to near the coast Tuesday afternoon. Coastal areas will likely see little or no clearing on Tuesday.

KSEA...VFR is expected throughout the night. Continued onshore flow favors a return of low clouds on Tuesday morning with IFR ceilings 12Z-18Z. Surface winds W/SW 7 knots or less will gradually veer to the N/NW late this afternoon and evening. Winds will back to S/SW again overnight.

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MARINE

Broad surface high pressure will remain centered over the offshore waters with lower pressure east of the Cascades through much of the week ahead. This will maintain onshore flow over the next several days and bring diurnally driven small craft advisory strength westerlies to the central and east Strait of Juan de Fuca daily. A series of weak systems passing to the north of the area throughout the week may help strengthen onshore flow at times for additional risks of gales along the central and eastern Strait.

Seas across the coastal waters at 3-5 feet today are expected to increase to 5-7 feet near midweek then persist within the 3-6 foot range through the second half of the week.

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FIRE WEATHER

A dry, onshore flow pattern with seasonable temperatures and persistent good to excellent overnight RH recoveries will continue through Tuesday. Ensembles continue to very confidently show an upper level shortwave clipping the area Wednesday, with some variability in the strength of the shortwave, as recent models have brought the shortwave a bit more south over our area. This will continue the scenario of thunderstorm potential Wednesday afternoon and evening for the northern Cascades, as well as the central Cascade. Latest guidance shows generally a 20-30% probability over the Whatcom, Skagit and Snohomish Cascades through late Wednesday evening. Warmer and continued dry conditions remain on track through the second half of the week, likely resulting in a return of elevated fire weather concerns for some areas. A southwest pattern flow over the weekend may keep thunderstorm chances in the forecast, primarily in the North Cascades.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 5 AM PDT Tuesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.