textproduct: Seattle/Tacoma

SYNOPSIS

A frontal system will move out of Western Washington into this evening. High pressure builds aloft over the Pacific Northwest Thursday and Friday, with just a slight chance of precipitation. The upper ridge further builds over the weekend for drier, warmer conditions.

SHORT TERM /TODAY THROUGH THURSDAY NIGHT/

Latest radar imagery shows rain showers dissipating over the region, along with the convergence zone in Snohomish County. Impressive QPF amounts the last 24 hours over the western slopes of the Olympics and North Cascades, with 2-3.5 inches of rainfall over these areas. The previous discussion can be found below along with updates to the aviation and marine sections:

Drier conditions develop Wednesday into Thursday as high pressure begins to build into the Pacific Northwest. Morning stratus and localized areas of fog due to residual moisture will clear for some sunshine during the afternoon. A system will weaken along the northern periphery of the ridge late Thursday, resulting in a slight uptick in rainfall potential beginning later Thursday into Thursday night, however any QPF amounts are expected to remain light, mainly focused on areas near the BC border. Highs mainly in the low to mid 60s Wednesday and Thursday.

LONG TERM /FRIDAY THROUGH MONDAY/

The aforementioned weakening system may continue to bring light rain along the northern tier, mainly North Cascades on Friday, but predominantly dry conditions are expected. Ensembles are in good agreement in the upper ridge building further over the Western US this weekend, with dry conditions and warming temperatures over Western Washington. Dry conditions look to continue into early next week, although an increase in onshore flow may result in slightly cooler temperatures by Monday. JD

AVIATION

Westerly flow aloft will continue into Wednesday with an upper ridge axis centered well south of the region. Post-frontal low level onshore flow will weaken overnight and become northerly on Wednesday. Weak convergence persists over central Puget Sound this evening producing a few showers and MVFR ceilings. Confidence in the overall forecast ceilings areawide overnight is not high. However, lighter surface winds and remnant low level moisture will favor the development of IFR or low MVFR stratus. Stratus that does form will lift and scatter toward midday on Wednesday with varying amounts of mid and high level moisture streaming across the area.

KSEA...As referenced above, MVFR ceilings are likely to hang around overnight and may drop to occasional IFR toward daybreak before lifting and scattering out toward 19Z or 20Z on Wednesday. Surface winds N/NE 6 to 9 knots easing overnight then becoming N/NW 7 to 10 knots Wednesday afternoon.

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MARINE

Surface high pressure building over the interior of British Columbia and weak troughing just offshore will lead to the development of some weak east/southeast flow on Thursday. Northerly or weak offshore flow will develop across area waters later Friday into the weekend as a thermally induced surface trough expands northward along the coast.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 2 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.