textproduct: Seattle/Tacoma

SYNOPSIS

A ridge of high pressure will produce a warming trend through Tuesday. A transition to onshore flow and cooler temperatures will take place on Wednesday along with a chance of some precipitation. Cooler and unsettled conditions are expected into the weekend as a trough of low pressure over the Northeast Pacific sends a series of weak frontal systems across the area.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

High pressure over the region will lead to dry conditions and warmer temperatures moving into Tuesday. Most areas will see high temperatures in the 70s to lower 80s on Tuesday (Minor HeatRisk), with pockets of mid/upper 80s in the Cascade valleys. The flow will be turn onshore during the afternoon and the warm-up will be brief along the coast.

The ridge kicks east and inland Tuesday night while a trough moves in from the west. The air mass will be slightly unstable with moist, diffluent flow, and we may see some showers and thunderstorms develop over Oregon and drift north during the overnight hours, mainly over the southern Cascades. Otherwise, with the return of onshore flow, Wednesday is looking cooler and in the 60s. And with the trough, we are seeing a chance of showers and wetting rain in the mountains with a few hundredths falling in the interior. Showers with a convergence zone may linger into Wednesday night. 33

LONG TERM /THURSDAY THROUGH MONDAY/

Western WA is under onshore flow on Thursday, leading to cool and cloudy conditions with a chance of showers. Convergence zone showers are expected near the King/Snohomish line. We'll see an uptick in shower activity on Friday as a larger trough drops down from B.C. Isolated thunderstorms are possible as the air mass will be slightly unstable (primarily during the afternoon and evening hours). This trough keeps us cool and showery on Saturday with high temperatures only in the 50s. Weak high pressure moves in early next week for drier weather and temperatures closer to average. 33

AVIATION

Westerly flow aloft will become southwesterly as the upper level ridge shifts eastward. Mostly clear skies with scattered high clouds will persist through Tuesday, the only exception remains the a chance of low cigs/vis Tuesday morning along the coast. N/NW winds 8- 12 kt today, becoming NE again under 5 kt tonight. There is a 15-20 chance of scattered thunderstorms Tuesday evening, mainly along the Pierce and Lewis County Cascades.

KSEA...VFR conditions with mostly clear skies, with scattered high clouds. NW winds 10-12 kt, will become NE and ease to 5-7 kt late this evening.

MARINE

A brief period of offshore flow Tuesday will accompany a thermally induced surface trough as it noses northward along the Oregon coast overnight. A system passing midweek will bring a 30-40% chance of showers over the interior waters. While winds for most waters will remain light through the week, there will continue to be pushes of winds (likely greater than 20 kt) through the Strait of Juan de Fuca at times. Wednesday continues to look like the strongest period with a 75% chance of gusts 25 knots or stronger through the central and eastern strait. Seas will hold around 4-6 ft through the week, with a brief bump to 6-8 ft with the midweek system.

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...None.