textproduct: Seattle/Tacoma

UPDATE

No major changes to the inherited forecast this evening. A decaying front is tracking across the area with little to no precipitation. Though, low-level onshore flow has picked up with 25 mph wind gusts observed over Whidbey Island so far tonight. Marine stratus will become widespread overnight into Wednesday morning. Low temperatures are forecast to bottom out between the lower to upper 50s. The previous discussion remains below along with an updated marine/aviation section:

SYNOPSIS

Warm conditions will persist for the interior today ahead of cooler conditions through the remainder of the week. A weak frontal system will bring slight chances of rain to higher elevations on Wednesday, with dry conditions through the rest of the week. Drier and warmer conditions are forecast early next week as high pressure builds over the western US.

SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/

Warm temperatures will remain in place across the interior today under southwest flow aloft as the next weather system approaches. Highs are on track to peak in the upper 70s to low 80s for areas surrounding and south of the Puget Sound. Areas along the water will see cooler temperatures today peaking in the 60s as onshore flow continues to bring in marine air.

A weakening frontal system will cross the region tonight into Wednesday morning, bringing in cooler temperatures alongside chances for drizzle. Weak convergence may form some showers behind the frontal passage over the northern Puget Sound, but confidence is low over whether this convergence would produce any measurable rainfall. Increased onshore flow will cause low stratus to expand inland Wednesday and Thursday mornings, with sunshine returning each afternoon. Highs will peak near normal in the mid 70s across the lowlands and in the mid 60s along the coast. In addition, with flow shifting onshore, smoke from nearby wildfires will remain north and east of western Washington.

LONG TERM /FRIDAY THROUGH TUESDAY/

A low pressure system stalled over Vancouver Island will swing a weak front across western Washington on Friday, bringing chances for light rain over the northern Olympic Peninsula and North Cascades. Elsewhere, onshore flow will continue to promote morning low clouds breaking up by the afternoon. This storm system will slowly meander eastward to the north, limiting chances for rain in western Washington over the weekend. Temperatures will continue to hover near normal on Saturday and Sunday, and instability from the nearby storm system will bring chances for isolated thunderstorms (5%-10%) along the Canada border.

High pressure will continue to build over the central US early next week, with a deep low pressure system dropping southward in the Gulf of Alaska. This will promote warmer temperatures across western Washington with southwest flow aloft, but uncertainty remains over the degree of warming by early next week. Ensembles show a most likely scenario of highs in the upper 70s to low 80s next Monday and Tuesday.

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AVIATION

A closed low over central British Columbia will maintain west/southwesterly flow over the area tonight. Expecting stratus to fill back into the region this evening, first along the coast then seeping inland with the help of a weak frontal system that will move across the area overnight into early Wednesday. Probabilities for MVFR or lower cigs will increase between around 10-13Z. Periods of IFR or lower conditions cannot be ruled out area-wide, though the highest likelihood is along the coast and into the Kitsap Peninsula. Expect cigs to scatter behind the frontal passage after around 18- 21Z Wed, with the exception of over the central Puget Sound area where post-frontal convergence will keep lower cigs and place and perhaps squeeze out some light showers or drizzle.

Relatively light winds expected for the remainder of the overnight with west to southwest winds turning more north in the late afternoon/early evening Wednesday.

KSEA...VFR conditions continue through late tonight. MVFR cigs expected to return after around 09-11Z Wed with periods of IFR possible, mostly likely between 13-17Z Wed. A slow lift is expected with low-end VFR conditions possible after around 21Z Wed. Convergence behind the front look to keep ceilings in the picture through much of the day.

Light west to northwest winds this evening will trend more southerly overnight, 5 kt or less. SW winds resume during the day and will likely turn to W to NW by Wednesday afternoon.

MARINE

Broad high pressure will continue over area waters through Thursday. A weak frontal system will move across the waters late tonight into early Wednesday. However, high pressure is expected to immediately rebuild behind the front. High pressure will weaken late in the week as a low pressure system prepares to swing south towards area waters. Onshore flow will continue the rest of the week through Strait of Juan de Fuca. A stronger push of westerlies has arrived this evening through the Strait of Juan de Fuca and a Gale Warning is in effect through Thursday morning. Small craft winds are also spilling into Admiralty Inlet this afternoon, and a small craft advisory will continue through the early overnight hours. Another strong push is expected Wednesday afternoon. Guidance still supports a 55-65% chance of gales through the Strait of Juan de Fuca Wednesday afternoon, and the Gale Warning has been issued Wednesday afternoon. Additional headlines are possible throughout the rest of the week.

Seas expected to remain below 10 ft through the weekend. Portions of the coastal waters may see steep seas on Wednesday/Thursday as seas build to 6-8 ft with a dominant period of 7-8 seconds.

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FIRE WEATHER

Fire concerns will remain low through the week with continued onshore flow bringing moist air into the region. This will promote higher humidities across western Washington with good overnight recoveries. Warming and drying is forecast early next week, though conditions are not expected to reach critical fire weather thresholds.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Gale Warning until 8 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning from 2 PM Wednesday to 5 AM PDT Thursday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 3 AM PDT Wednesday for Admiralty Inlet.