textproduct: Seattle/Tacoma

SYNOPSIS

A cold upper level trough will continue moving east into Western Washington this afternoon and remain over the area through Saturday night. An upper level ridge builds offshore on Sunday, with Western Washington remaining on the backside of the ridge through the middle of next week.

SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/

Broad showers continue across Western Washington this afternoon. The fairly extensive cloud cover. Destabilization could lead to thunderstorm activity today with at least a 15-20% chance of thunder area wide, meanwhile the best chances (25-35%) will be along the coast and into the north interior. Lightning, small hail, and brief heavy downpours will be the primary hazards. A Winter Weather Advisory was added for the mountains of western Washington above 4000 feet. This was put out mainly as a heads up for those with outdoor recreation plans today through Saturday night. Snow showers and thunderstorms cannot be ruled out. Road travel conditions could see minor temporary impacts, but generally ground temperatures will be warm enough to limit road accumulation.

Widespread chances for thunder exist through Saturday, though the focus of the convective potential will shift into the central Puget Sound south through SW Washington (peaking in the 25-35% range). Shower coverage then quickly decreases into Sunday with an upper ridge building offshore. The ridge axis will remain far enough away, and in combination with lower-level moisture, will expect to see abundant cloud cover that may be a bit persistent through the morning and perhaps midday hours. Afternoon sunshine should result, bringing highs back to the lower to mid 60s Sunday.

LONG TERM /MONDAY THROUGH FRIDAY/

Ensemble guidance remains in good agreement with the upper level ridge remaining in place at least through Tuesday. Differences in the model solutions beginning Wednesday with some solutions moving the ridge inland over Western Washington while other solutions keep the ridge axis offshore. Either scenario keeps the weather dry over the area. The ridge axis moving overhead would result in a little warmer days. For now with the uncertainty will keep highs just a couple of degrees above normal Wednesday and Thursday, in the mid 60s to lower 70s. Highs Monday and Tuesday in the 60s. Lows in the 40s through the period.

AVIATION

W/SW flow aloft through tonight, veering to the NW Saturday morning and then more northerly late Saturday night. At low levels, S winds for all but the coast, where winds are W. Speeds ranging 10-15 kts with gusts up to 25 kts. Widespread rain showers (and slight chance for thunderstorms) leading to MVFR ceilings and isolated IFR. Similar conditions are in store for tonight into Saturday morning as rain showers persist. Gusts up to 20 kt are possible for Puget Sound terminals until 10-12z Sunday. Low-end VFR and MVFR is in store for Sunday as well as showers maintain.

KSEA...Low-end VFR and MVFR ceilings have been observed so far this afternoon with widespread rain showers. Similar conditions are expected tonight into Saturday. Southwesterly winds 10-15 kts with gusts to 25 kt will maintain before gradually easing late tonight. For Saturday, HiRes ensembles consistently showing the development of a PSCZ Saturday afternoon with a 40-50% chance of northerly winds at the terminal by 22z, and higher odds by 00-01z Sunday. In addition, there is 15 to 20% chance of lightning with the convergence zone through the same period.

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MARINE

A system passing through the area tonight into Saturday will enhance winds and seas over most area waters with small craft advisory conditions developing over the coastal waters after midnight tonight then the Strait of Juan de Fuca Saturday morning. In addition there will be a slight chance of thunderstorms for most area waters overnight into Saturday morning. On Saturday seas over the coastal waters will be near or above 10 ft, becoming steep Saturday evening. Persistent onshore flow will result in daily pushes of through the Strait of Juan De Fuca into next week.

HYDROLOGY

The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated during this time as needed.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory until 8 AM PDT Sunday for Cascades of Pierce and Lewis Counties-Cascades of Snohomish and Northern King Counties-Cascades of Southern King County- Cascades of Whatcom and Skagit Counties-Olympics.

PZ...Small Craft Advisory until 7 PM PDT this evening for Puget Sound and Hood Canal.

Small Craft Advisory from 11 PM this evening to 11 PM PDT Saturday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.