textproduct: Seattle/Tacoma

SYNOPSIS

Zonal flow aloft and onshore flow will maintain seasonable conditions with morning clouds and afternoon sunshine again today. 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 /TODAY THROUGH THURSDAY/

Marine stratus not quite as successful as it was 24 hours ago on its eastward progression, although now is not the time to sell it short as additional advancement is likely this morning, as hinted at by stratus getting into Whidbey Island as well as northern portions of Snohomish county. Morning temperatures pretty much even keel with those from this time yesterday.

One last day of the current weather pattern, zonal flow aloft and onshore winds, strongest in the afternoon and evening. Daytime temps will depend on how much additional eastward progress marine status makes. As stated above, since it is a little bit shy of what it was yesterday, should see an earlier burn off and as such perhaps a degree or two of warming.

Upper level trough for Wednesday is still on track as models want to dig this feature a little further south than previous runs. For the thunderstorm risk to Olympics, it makes sense, as some model solutions had been hinting at that and have consistently shown the instability will be there for it...so have allowed that change to seep into the forecast. Best chances for precip still favor the higher terrains of the area and with a more southern track now progged, this will allow for shower/thunderstorm chances to sag down into the Cascades of Snohomish county and maybe even the far northeastern corner of King county. This system does not linger and any precip/lightning threat should be wrapped up by midnight Wednesday night.

A general trough pattern remains over the Pac NW Thursday and latest solutions seem to be trying very hard to bring in wrap around moisture...but coverage looks very splotchy at best. An argument could be made for the terrain of the Cascades...but solutions that include the Olympics have a harder time making their case convincing. Left it in forecast for now, but if no activity occurs there Wednesday. the chances for Thursday would likely be nil.

Daytime highs Wednesday will take a slight tumble, with the interior lowlands in the lower to mid 70s and the coast around the mid to upper 60s. Thursday wastes no time rebounding, however, as upper 70s to lower 80s return inland...although no significant change for the coast.

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LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

The upper level trough slowly cycles out of the area Friday as an upper level ridge building over the Rockies ends up being the primary weather driver for the weekend into next Monday. While this may not advance the warming seen on Thursday, interior daytime highs will linger in the upper 70s to lower 80s for the remainder of the forecast period as the coast continues to favor mid to upper 60s...with a few spots getting up to 70. Earlier solutions showed a stronger warming trend during this time, which would have elevated fire weather concerns for the end of the forecast cycle. Will not back away from this thinking just yet, but if this somewhat cooler solutions persists, daytime RH values would remain north of 40 pct, which, given the time of year, is not terrible.

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AVIATION

Westerly flow will continue aloft with onshore flow in the low levels. Another round of stratus is pushing inland early this morning, though its extent across the interior will likely be less than that of yesterday. Areas across the interior in stratus will likely see ceilings dip down to MVFR/IFR for a few hours this morning before stratus scatters out and retreats back to the coast between 17-19Z. VFR conditions will then resume this afternoon and persist through this evening for the majority of the area terminals. Coastal areas will likely hang on to the stratus a bit longer, with scattering not expected in spots until this afternoon, though some areas along the coast may not even scatter out at all.

KSEA...Conditions remain VFR early this morning, though continued onshore flow favors a return of some low clouds into the terminal between 12Z-18Z. May see more SCT clouds make it into the terminal versus a BKN or OVC deck given the latest progression of stratus on satellite. Surface winds are primarily out of the W and light at 5 kt or less. Winds will briefly shift back to S/SW early this morning, but will transition back to the north by this afternoon.

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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. Stronger onshore flow will develop at times throughout the week as a series of weak systems passes to the north of the area. This may bring additional risks of gales along the central and eastern Strait at times.

Seas across the coastal waters will primarily persist between 2-4 feet today are expected to increase to 5-7 feet near midweek. Seas will then subside back to 3-5 feet heading into the weekend.

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FIRE WEATHER

A dry, onshore flow pattern with seasonable temperatures and persistent good to excellent overnight RH recoveries will continue today. 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 the CWA. This will continue the scenario of thunderstorm potential Wednesday afternoon and evening for the northern and central Cascades. 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, although the warming seems to be capped in the latest solutions. It is a little early to back away from expecting warmer and dry conditions into the start of next week...resulting in elevated fire weather concerns. If current solutions remain consistent, daytime RH values may not take the hit initially expected in this time frame, staying above 40 pct for the majority of W WA. Stay tuned.

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SEW WATCHES/WARNINGS/ADVISORIES

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

Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.