textproduct: Seattle/Tacoma

SYNOPSIS

Weak high pressure remains in place today, but will become more zonal into the weekend. Onshore flow will increase over the next several days. A system arriving on Memorial Day will bring widespread rain and cooler temperatures to the region. The rest of the front will move through on Tuesday, keeping showers in the forecast. Weak ridging is possible through the second half of the week.

SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/

Weak high pressure aloft will transition to more zonal, onshore flow through the weekend. This will enable a deeper push of marine stratus into the interior each of the next few mornings. While the onshore push looks a bit more extensive and will likely linger a bit longer through the morning Saturday, there's likely to be some improvement in the afternoon. This will bring some sunshine to the interior and afternoon highs in the upper 60s to around 70 each day. This will maintain only Minor HeatRisk across most of the lowlands. The onshore flow will also strengthen the westerly winds through the Strait of Juan de Fuca over the weekend.

LONG TERM /MONDAY THROUGH FRIDAY/

The zonal flow will open the door to the next system arriving late Sunday night into Monday. This will bring breezy, cool, and wet conditions to Western Washington for the Memorial Day holiday. Amounts of around a half inch of rain in the lowlands and one to one and a half inches in the mountains are expected. Additionally, though the instability late Monday afternoon and evening looks rather modest, there's still around a 10-15% chance of a flash of lightning or two especially near the coast or from Puget Sound southward. In addition to the rain, we'll see rather breezy winds with gusts up to 20-30 mph across much of the area as this weather system moves through. While these speeds are not generally strong enough to cause widespread impacts, unsecured tents or outdoor equipment could be impacts. With this cooler air mass in place, temperatures are unlikely to climb out of the 60s. Showers linger early Tuesday as the upper trough moves past the area, with a return to dry conditions late Tuesday through midweek as weak high pressure again rebuilds.

AVIATION

An upper level ridge centered offshore will weaken overnight into Saturday with west to northwest flow aloft continuing. Increasing low level onshore flow ahead of a weak system moving into British Columbia will bring coastal stratus into the interior lowlands overnight. Widespread IFR or low MVFR ceilings are expected west of the Cascades on Saturday morning. The stratus is expected to gradually lift and scatter by 21Z Saturday for the interior areas, but will linger along the coast for the entirety of Saturday.

KSEA...VFR is expected through this evening. IFR or low MVFR stratus will reach the terminal by around 10Z Saturday and persist into midday Saturday before scattering out mid-afternoon. Surface winds west to northwest 7 knots or less will back to southwesterly late this evening and increase 7 to 10 knots Saturday morning.

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MARINE

Surface high pressure centered well offshore will continue to produce onshore flow into the weekend. A system passing well north of the waters will increase onshore tonight into Saturday. This will lead to advisory level westerlies in the central/east strait tonight and near gale westerlies Saturday evening. The offshore ridge will weaken and shift southward on Sunday as a frontal system associated with a vertically stacked low west of Haida Gwaii approaches the area. This system is expected to produce advisory level winds across much of the waters Monday along with seas building to at or above 10 feet over the coastal waters Monday into Tuesday. Weak surface ridging rebuilds offshore later Tuesday into Wednesday.

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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...None. PZ...Small Craft Advisory from 7 PM this evening to 3 AM PDT Saturday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.