textproduct: Seattle/Tacoma

SYNOPSIS

Upper level low approaching from the southwest Friday will move into the coastal waters Saturday and into Southern British Columbia early Sunday morning. This system will bring cooler weather with a chance of showers and thunderstorms. Upper level ridge rebuilding Sunday will move east Monday for dry and mild weather. Upper low shifting inland on Wednesday with showers returning.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

Weak high pressure is over the area for dry and mild conditions. The air mass will be a little warmer on Friday with pockets of Moderate HeatRisk in the interior and Cascade valleys (highs in the mid to upper 80s).

The next weather system rolls in late Friday and into Saturday. This system will bring cooler conditions, showers, and a threat of thunderstorms to western Washington. The highest instability will be over the Olympics and northern Cascades where scattered thunderstorms may develop - leading to elevated to critical fire weather conditions. The highest probability of seeing wetting rains will be near the Canadian border. There's a 10-20 percent chance (isolated coverage) of seeing thunderstorms in the lowlands from Seattle northward. With the cooler air mass in place, temperatures will track cooler than average and in the 60s to lower 70s. 33

LONG TERM /SUNDAY THROUGH THURSDAY/

Showers (mainly north part) will linger into Sunday as the low tracks N/NE into B.C. Dry and mild weather will return early next week with low pressure offshore and weak high pressure inland. Temperature ranges will be close to average each day. Low pressure shifts inland Wednesday and Thursday for a chance of showers. 33

AVIATION

VFR this afternoon with mostly clear skies. A weak push of marine stratus will bring IFR/LIFR conditions to the coast this evening into Friday morning. The stratus will attempt to push into OLM, but don't expect reach Puget Sound terminals. Reductions in visibility highly likely with the stratus. Additionally, patchy fog possible in the valleys of the southern interior and northern interior. Mid-to- high clouds will increase Friday morning with conditions remaining VFR across interior terminals. Minimal improvement along the coast on Friday, with conditions likely only rebounding to MVFR. Generally NW winds this afternoon, easing tonight.

KSEA...VFR with mostly clear skies today and increasing mid-to-high clouds Friday morning. NW winds this afternoon 6-8 kt will transition to NE this afternoon, easing tonight to 3-5 kt.

29

MARINE

Broad high pressure over the waters will weaken Friday. A weak surface low will move into the coastal waters Saturday with the associated system moving through the inland waters Saturday morning into early afternoon. The low will dissipate Saturday night. Additionally, there is a slight chance (10-20%) for thunderstorms on Saturday for both the coastal waters and interior waters. High pressure will rebuild Sunday and remain over the area through Monday. A cold front will move over the waters on Tuesday.

Winds will pick up behind the system on Saturday. Guidance suggests there is a 40-60% wind gusts may approach near 21 kt through the Strait of Juan de Fuca, with winds above 21 kt staying on the Canadian side.

Seas remaining mostly in the 3 to 5 foot range for the next few days. Felton/29

FIRE WEATHER

Warm, dry conditions continue into Friday. Moderate RH recoveries are expected tonight for the Cascades. An upper low will move northwards towards Western Washington late Friday into Saturday. This feature will result in the development of convection during this period. Probabilities for convection are highest over the Olympics and North Cascades, peaking between 20 to 30 percent. Due to the potential of scattered thunderstorms for these areas, a Fire Weather Watch has been issued for zones 652, 658, and 661. Convection may exist elsewhere, including the southern Washington Cascades, however, uncertainty exists in the coverage for these regions. Showers and thunderstorms may begin as early as 11PM-2AM Friday night over the Olympic Peninsula, with the threat continuing through late Saturday. Lightning may lead to new fire starts, as well as result in gusty and erratic winds.

Onshore flow increases Sunday into early next week, resulting in cooler conditions and increased RH values. Rain may linger into Sunday for the North Cascades, with another slight chance of showers later Tuesday into Wednesday. JD

SEW WATCHES/WARNINGS/ADVISORIES

WA...Fire Weather Watch from late Friday night through Saturday evening for West Slopes of the North Cascades Generally above 1500 Feet.

Fire Weather Watch from late Friday night through Saturday evening for East Portion of the Olympic Mountains-West Portion of the Olympic Mountains.

PZ...None.