textproduct: Seattle/Tacoma

SYNOPSIS

Upper level trough moving out of the area this morning. Upper level ridge building this afternoon and remaining through Thursday. Weak system moving by well to the north Thursday night into Friday. Strong upper level ridge building offshore Friday with the ridge nosing into British Columbia Saturday. Low level flow going offshore Saturday night as thermally induced surface trough builds along the coast. Upper level ridge weakens Monday night with the low level flow turning onshore Tuesday. Ridge continues to weaken Wednesday with stronger low level onshore flow.

SHORT TERM /TODAY THROUGH FRIDAY/

Satellite imagery shows cloudy skies for the most part over Western Washington early this morning. Wave clouds present over the east slopes of the Cascades indicating we still have strong flow aloft. Doppler radar has convergence zone over Snohomish county, rain shadow over the Central Puget Sound and scattered showers elsewhere. Temperatures at 2 am/09z were in the upper 40s to mid 50s.

Upper level trough exiting the area this morning. Surface gradients weakening which could allow the convergence zone to drift south possibly into King county this morning before dissipating. Upper level ridge building this afternoon with the low level flow turning northerly. This will help dry out the air mass giving the area some sunshine after the morning cloud cover. Air mass aloft still a little on the cool side so even with the sunshine highs a touch below normal, in the 60s.

Upper level ridge over the area tonight and Thursday with light or northerly flow in the lower levels. This will limit the cloud cover Wednesday night/Thursday morning making for a sunny day. Clearing tonight leading to a cool morning Thursday with lows mostly in the 40s. Colder locations getting down to the upper 30s. Highs warmer Thursday, in the mid 60s to mid 70s.

Weak system moving by well to the north Thursday night into Friday will flatten the upper level ridge and induce weak low level onshore flow. This will keep highs in the mid 60s to mid 70s Friday. Lows Friday morning in the 40s and lower 50s.

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

Good consistency in the models with a strong upper level ridge building offshore Friday night. The ridge will move east and nose into British Columbia Saturday. 500 mb heights rising from the lower to mid 570 dms Friday afternoon to the lower to mid 580 dms Saturday afternoon. Northwesterly flow in the lower levels with afternoon seabreezes knocking a couple of degrees off the highs near the water. Highs Saturday in the mid 70s to mid 80s.

Ridge remaining over the area Sunday and Monday. Low level flow turning offshore as thermally induced surface trough develops along the coast Saturday night. Temperatures aloft continue to warm with model 850 mb temperatures peaking around plus 20C Monday. High temperatures warming into the 80s and lower 90s Sunday with the warmer locations in the mid 90s Monday. Record highs are likely Sunday and very likely Monday.

Model solutions becoming a little inconsistent Tuesday. Yesterday's runs favored a marine push. There are more ensemble solutions on the latest run going for a just a weak push as the upper level ridge hangs on a little longer and the thermally induced trough doesn't move inland until afternoon. Tough call this far out. Current blend forecast leaning towards a stronger push, high temperatures dropping 10-15 degrees versus the weaker push scenario, a 5-10 degree drop.

Minor HeatRisk Saturday becoming moderate Sunday and Monday. Probably of major HeatRisk Monday from Seattle Southward including the lower Chehalis Valley and the Cascade foothills has dropped to 20-40% from 40-60% yesterday. In addition to the HeatRisk the clouds and rain recently has prevented the water temperatures around the area from rising. Lake Washington and Lake Sammamish water temperatures currently only 62 degrees. Area rivers are even colder. Lets play it safe around the water during this short warm spell. Felton

AVIATION

A mix of MVFR and VFR cigs early this morning as scattered showers continue to move across the area. Expect shower activity to gradually diminish throughout the morning hours. Guidance continues to suggest that MVFR cigs could be reintroduced between 15z-19z for terminals that have managed to stay VFR. Improvement to VFR for all terminals expected after 18z-20z and will prevail throughout the day. Southerly flow will shift northerly across the terminals by this afternoon as high pressure builds over the region.

KSEA...MVFR cigs early this morning at the terminal. Improvement to VFR expected after 18z-19z. Elevated southerly winds will continue to dwindle throughout the morning hours. Northwesterly flow 4-6 kt in the afternoon after 20z-23z, becoming northeasterly after 06z.

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MARINE

High pressure will continue to rebuild over the coastal waters today. Winds have decreased below gale criteria, and the Gale Warning has been downgraded to a Small Craft Advisory. Another westerly push across the Strait of Juan de Fuca is expected this evening, with high-res guidance suggesting an 70-80% chance of winds exceeding 21 kt across the central and east portions. In addition, guidance is suggesting another push through the central Strait Thursday evening. Latest probabilities are around 65-80% for small craft thresholds. As the week progresses, strengthening high pressure will build over the inner waters as well, leading to increased northerly surface flow across area waters. Latest guidance suggests winds should remain below small craft thresholds (20-40% chance over the coastal waters). Seas will remain below 10 ft going into the weekend as high pressure prevails over area waters.

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FIRE WEATHER

Wetting rains the last two days significantly slowed the drying of the fuels around Western Washington. Warming temperatures and the return of offshore flow Sunday and Monday will do a good job drying the area once again. Minimum relative humidity values as low as the teens Sunday and Monday. Fine fuels have not reached critical thresholds but the low level offshore flow Sunday and Monday will allow them to cure putting them close to critical levels by early next week. Larger fuels are drying out as well. Fire concerns will be elevated over the weekend peaking Monday. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 5 AM PDT early this morning for Central U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 3 PM PDT this afternoon for East Entrance U.S. Waters Strait Of Juan De Fuca.