textproduct: Seattle/Tacoma

SYNOPSIS

A ridge will weaken tonight with the low level flow turning onshore. Upper level trough moving through on Wednesday. Cold upper level low moving into the area Friday and Saturday for showers and a chance of thunderstorms. Weak troughing over the Pacific Northwest early next week with temperatures close to average.

SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/

Latest satellite imagery already shows clouds moving back into western Washington tonight. The switch back to onshore flow will bring more moisture and cooler conditions and to the region on Wednesday, helping alleviate fire weather conditions. Highs will track a good 15-20 degrees cooler than today with highs in the 60s to lower 70s. A trough will bring a few showers to the coast and mountains too. The air mass will be slightly unstable over the North Cascades where there's a slight chance of afternoon thunderstorms (near the crest).

Thursday is dry but we remain under onshore flow. Expect morning clouds with afternoon sunbreaks and highs near average. 33/14

LONG TERM /FRIDAY THROUGH TUESDAY/

A deep low will spin off B.C on Friday then shift inland on Saturday, keeping the weather cool and showery over western WA. Highs both days are only around 60 degrees with morning lows in the 40s. The air mass will be cool and unstable with a chance of thunderstorms Friday night and again Saturday afternoon. Showers with a Puget Sound Convergence Zone are expected on Saturday in the interior with a threat of thunderstorms. Shower activity will taper down Saturday night as the low exits east and weak high pressure moves in from the west. This ridge keeps us mainly dry moving into Sunday. Looking ahead, weak upper level troughing over the region will bring a chance of showers with temperatures close to average early next week. 33

AVIATION

Widespread VFR across the terminals this evening with some high clouds passing through. An incoming frontal system will lead to an increase in mid to high clouds tonight. Ceilings will gradually decrease overnight into the morning hours, however the majority of terminals are expected to remain VFR. The only exception, being terminals along the coast. Ceilings will deteriorate along the coast late tonight to MVFR. Latest guidance suggests there is a 20-30% chance of IFR/LIFR cigs between 06z-10z. There is an isolated risk (15-20%) of thunderstorms for the northern Cascades Wednesday evening. However, not expecting any impacts to any of the terminals. WNW winds will continue today, with more widespread SW winds returning after 06z. Onshore flow will increase Wednesday morning, after 10z. Gusts between 15-20 kt possible for Puget Sound and Northern Interior terminals.

KSEA...VFR conditions will continue through Wednesday. Mid to high cloud cover expected to increase tonight. WNW today 4-6 kt. Winds have transitioned more southerly so far this evening. Guidance continues to highlight increased SW winds between 10z-16z, with gusts to 15 kt possible (70-80% chance).

29/41

MARINE

High pressure will continue to weaken this evening as a cold front is expected to move over area waters on Wednesday. Diurnal pushes across the Strait of Juan de Fuca will occur throughout the week. Latest guidance suggests that the strongest push will be Thursday evening with high-end small craft winds likely. The chance for gales remains low, with current chances remaining at 10%. Additional systems are expected to move over the waters late in the week and into the weekend. An upper level low will track over the waters Friday through Saturday, leading to an unstable airmass. Consequently, there is a small chance (15-20%) of thunderstorms. As for Friday, thunderstorms are possible for all area waters, with the highest chances for the coastal waters. As the low pushes inland on Saturday, the chances of thunderstorms shifts to the interior waters, with the highest probabilities for Puget Sound.

29/41

FIRE WEATHER

A flip to onshore flow tonight will bring cooler conditions on Wednesday with higher RHs, alleviating fire weather conditions across western Washington through the second half of the week. 33/14

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 2 AM Wednesday to 11 AM PDT Thursday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.