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 SUNDAY NIGHT/

High pressure over the region is bringing one more warm and dry day to western Washington today. Highs in the interior are in the 80s with pockets of Moderate HeatRisk (mainly east of I-5). Satellite does show some wildfire smoke over western Washington due to light east winds over the crest. Sensors are showing degraded air quality in portions of Whatcom County and King County (due to the Three Queens fire). The air quality should improve on Saturday as the wind flow changes directions.

Our next system will move in late tonight and into Saturday and Sunday. This system will bring cooler weather along with increasing chances of thunderstorms. The highest chances of thunderstorms will be in the mountains, especially across the northern Cascades. The highest chances of wetting rains will be near the Canadian border. With the colder air mass in place, Saturday's highs will be cooler and in the 60s to lower 70s across most areas. Showers will linger on Sunday (mainly north part) as the low tracks N/NE into B.C. 33

LONG TERM /MONDAY THROUGH FRIDAY/

High pressure returns early next week for more dry and mild weather. The flow remains onshore with temperatures close to average. The ridge will stall an upper low offshore that will eventually shift inland by midweek for another round of showers. The low and cooler air mass will result in below average temperatures in the 60s and lower/mid 70s. We're under weak troughing through the end of the week with isolated mountain showers. 33

AVIATION

Southerly flow aloft will increase tonight into Saturday as an upper low offshore approaches Western Washington. VFR cigs for the majority of terminals this afternoon with increasing mid and high clouds. MVFR/IFR stratus continues along portions of the coast. Stratus will move inland into Puget Sound into Saturday morning, resulting in more widespread MVFR/IFR cigs. LIFR stratus will exist along portions of the coast tonight into Saturday as well. Showers and a few thunderstorms are expected to develop late tonight into Saturday. Probabilities for thunderstorms range to 10 to 20 percent for all terminals, with the higher probabilities from KPAE northwards. Cigs will improve to VFR for interior locations by the afternoon. W/NW winds this afternoon will transition more SW tonight and increase into Saturday.

KSEA...VFR with mid and high clouds into tonight. Stratus will spread inland early Saturday, reaching the terminal around 12z. Predominantly low-end MVFR cigs are expected. There is a 20% probability of IFR cigs between 13 to 17z as well. Cigs will slowly improve to VFR into the afternoon, between 19 to 21z. Showers and a few thunderstorms are expected to develop early Saturday morning. Confidence remains lower in the exact location for precipitation, but there is a 10 to 15% probability for thunderstorms around the terminal Saturday, peaking between 12 to 20z. W/NW surface winds ranging 5 to 8 kts will transition SW after 00-01z. JD

MARINE

Onshore flow will increase this evening resulting Small Craft westerly winds through the Strait of Juan de Fuca tonight. A weak surface low then moves into the coastal waters Saturday before the low dissipates Saturday night. Showers will develop late tonight into Saturday associated with the system. There is a also a slight chance (10-20%) for thunderstorms over both the coastal and interior waters on Saturday. South to southwest winds will also increase on Saturday, with gusts ranging 15 to 20 kts for portions of the interior waters and inner coastal waters. High pressure rebuilds Sunday and remains over the area into Tuesday. A cold front moves into the waters by midweek.

Seas will mostly be in the 3 to 5 foot range into early next week. JD

FIRE WEATHER

Dry and warm conditions continuing today. Critical RHs have been observed for locations above 2500 ft so far this afternoon. Increasing cloud coverage and continued low- level onshore flow this evening. Then, an upper-low offshore will track into the region late tonight into early Saturday with the potential for scattered showers and thunderstorms. As a result, a Red Flag Warning has been issued for the Cascade and Olympic Mountains late tonight into Saturday evening. The North Cascades are currently the most favorable for thunderstorms at this time with a 30-40% chance. Lightning may lead to new fire starts, as well as result in gusty and erratic winds.

Low level onshore flow increases Saturday night into Sunday with varying degrees of onshore flow through the middle of next week. Good relative humidity recoveries each night will keep fire weather concerns at a minimum. Chance of showers and possible thunderstorms next Wednesday with an upper level trough moving into the area.

41

SEW WATCHES/WARNINGS/ADVISORIES

WA...Red Flag Warning from 5 AM to 8 PM PDT Saturday for West Slopes of the North Cascades Generally above 1500 Feet.

Red Flag Warning from 1 AM to 5 PM PDT Saturday for East Portion of the Olympic Mountains-West Portion of the Olympic Mountains-West Slopes of the Central Cascades Generally above 1500 Feet.

PZ...Small Craft Advisory from 6 PM this evening to 6 AM PDT Saturday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.