textproduct: Seattle/Tacoma

SYNOPSIS

Dry conditions will persist through early Thursday as an upper level ridge builds over Western Washington, bringing the chance for morning fog or low stratus. The ridge will weaken late Thursday as the next frontal system arrives, bringing lowland rain and mountain snow. Unsettled and cooler conditions continue into the weekend, with additional systems expected to move over the region.

SHORT TERM /TODAY THROUGH FRIDAY/

As a weak upper level ridge nudges into western Washington, areas of fog and low stratus will continue to expand southward along the Salish Sea and Puget Sound this morning. Mostly clear skies will break out of the low stratus and fog by the late morning to early afternoon, allowing high temperatures to reach the upper 40s to lower 50s. Clouds will begin to filter in across the region later this evening as the next frontal system slowly approaches. However, with weak high pressure remaining in place, another round of fog and low stratus is possible Thursday morning, with similar temperatures to today.

The next frontal system will cross the Pacific Northwest later on Thursday, bringing in the next round of more widespread precipitation. Snow levels will lower to near 3000 feet overnight into Friday as the system digs into the region, with light snow accumulations through the Cascade passes. Precipitation will taper off late in the day Friday, with another system on its heels. Friday will cool several degrees, with most locations seeing high temperatures in the mid 40s.

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

Models remain in good agreement over unsettled conditions through the remainder of the forecast period. By Monday, an upper level trough is slated to dig southward into California, bringing slightly cooler air into western Washington. This may bring potential for snow to mix with rain at lower elevations overnight into Tuesday, though confidence is low over any accumulations or impacts. Chances for precipitation will continue across the region through the long-term, with light rainfall accumulations across the lowlands and several inches of much needed snow accumulation over the mountains.

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AVIATION

A weak upper ridge remains over Western Washington today with light northerly flow aloft. Low level flow remains northerly and will weaken tonight. Areas of IFR/LIFR in stratus and patchy freezing fog will persist around Puget Sound, the Southwest Interior, and portions of the Strait of Juan de Fuca before dissipating most areas midday. More extensive low cloud is expected across the area late tonight into Thursday morning as surface flow turns light.

KSEA...A period of IFR ceilings and northerly surface winds looks increasingly likely for a period this morning as IFR stratus over northern portions of Puget Sound begins to spread southward toward the Seattle area. Current thinking is to include a period of predominant low IFR ceilings from 12Z to at least 17Z before it scatters out to VFR toward midday. A return of IFR or LIFR ceilings are likely again Thursday morning. Surface winds northerly 8 to 12 knots easing to under 8 knots this afternoon, turning light and variable late this evening, then shifting to light southerly Thursday AM.

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MARINE

A weak surface ridge will remain over area waters into Thursday. Northerly flow across much of the waters today will turn southerly on Thursday as a frontal system moves into the British Columbia coast then dissipates over Western Washington early Friday. A stronger system will follow late Friday into Saturday and will begin a more active period this weekend into early next week with headlines likely at times for both wind and seas.

Seas 5 to 7 ft will build well into the double digits late Thursday into Friday before subsiding to near or just below the 10 foot mark over the weekend and early next week.

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HYDROLOGY

No river flooding is expected over the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

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