textproduct: Seattle/Tacoma

SYNOPSIS

Dry and mild weather will persist through midweek. Shower and mountain thunderstorm chances increase heading into Friday and Saturday as the next system moves in. Quiet weather returns for the first half of next week.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

Generally mild/benign weather for western WA through midweek. Currently, we sit under weak/split flow with high pressure to our south and low pressure offshore. The flow pattern remains onshore with temperatures close to average. High pressure remains nearly stationary moving toward midweek with ongoing dry weather across western Washington. 33

LONG TERM /THURSDAY THROUGH MONDAY/

Low pressure starts to shift east and inland Friday and Saturday for a chance of showers and cooler conditions. Most of the shower activity will be over the coast and mountains and there is a slight chance of thunderstorms in the northern Cascades Saturday afternoon. With the trough overhead, Saturday's highs will be cooler and in the 60s to lower 70s. The trough exits east Saturday night and we're back to our dry and mild conditions Sunday and Monday with temps very close to our averages. 33

AVIATION

VFR conditions remain in place this evening for much of W WA, aside from the coast where IFR to LIFR cigs have already developed. Lower cigs will move eastward through the night with at least MVFR conditions expected at remaining terminals by early Tuesday morning, although IFR to LIFR conditions are possible for CLM and PWT. Some reductions in vis will also be possible during this time as well. Cigs expected to lift with widespread VFR conditions returning by early afternoon. NW winds this evening and tonight will shift SW by Tuesday morning.

KSEA...VFR conditions this evening and early tonight. Another push of marine stratus is expected to bring MVFR cigs to the terminal around 12z. Clouds expected to lift and scatter in the afternoon after 18z. NW winds this evening around 5-7 kt will transition to SW late tonight into Tuesday morning around 3-5 kt. Afternoon wind speeds expected to increase to 6-9 kt.

MARINE

High pressure will remain over the far offshore waters and slowly build into area waters through the middle of the week, which will maintain northwesterly winds over the coastal waters. A weak system will approach area waters on Tuesday, with little impact to the waters. Northwesterly winds look to increase late tonight into Tuesday over the outermost waters, which may develop steep seas around 6-7 ft with a dominant period of 7 seconds. The threat for steep seas may continue through mid-week. High pressure will weaken late in the week as a frontal system passes over the coastal waters. Weak westerly pushes down the Strait of Juan de Fuca will continue this week. The next round of westerlies that may exceed 21 kt is Friday, with the latest probabilities around 40-60%.

62/29

FIRE WEATHER

The weather pattern will remain fairly stagnant over the next few days, with onshore flow promoting healthy relative humidity values. An upper level ridge will build northward towards the Pacific Northwest during the latter half of the week, bringing a mild warming and drying trend to western Washington.

The next weather system is favored to cross the region late Friday into the weekend, with potential for thunderstorms to develop over higher terrain leading to elevated fire weather conditions. While precipitation amounts may bring localized wetting rains to the region, any storms that develop will also be capable of generating gusty and erratic outflow winds and abundant lightning. While the exact timing and location of thunderstorms remains uncertain at this time, the threat of overnight thunderstorms remains into the weekend, particularly Friday night into Saturday.

15

SEW WATCHES/WARNINGS/ADVISORIES

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