textproduct: Seattle/Tacoma

SYNOPSIS

An upper level ridge centered well offshore with northwesterly flow aloft and light low level onshore flow will maintain dry conditions through the weekend with slightly above normal temperatures, warmest on Friday. Dry weather then continues into early next week, with temperatures becoming warmer as an upper level ridge builds over the region.

SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/

Considerably cooler conditions were observed across the area today with temperatures running only a touch above normal. The next couple days will be in the same ballpark before a short duration warming trend on Friday. Then our attention turns toward another potential warm spell arriving early next week. Current forecasts are on track. Previous discussion follows with update to aviation portion.

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Minimal change is expected with the weather pattern tonight through Wednesday night. The short term forecast remains highlighted by dry conditions with seasonable temperatures. An upper level ridge centered well offshore is expected to remain in place, with northwesterly flow aloft over western Washington. While low-level onshore flow is also expected to remain in place, the strength of the onshore flow will begin to weaken Tuesday night through Wednesday night. As such, some locations may end up a degree or two warmer on Wednesday, especially in areas away from the Puget Sound with minimal morning cloud cover.

Models and their ensembles suggest northwest flow aloft will continue Thursday through Thursday night, with the low level flow going light. This will result in mostly clear skies on Thursday with slightly above average temperatures. The deterministic NBM suggests highs will reach into the mid 70s to lower 80s over the interior lowlands on Thursday, except 60s along the coast and mid 80s over the lowlands of Lewis and southern Thurston Counties and the middle Chehalis River Valley. -23

LONG TERM /FRIDAY THROUGH TUESDAY/

The long term forecast is highlighted by continued dry weather and a warming trend, aside from a brief cooldown over the weekend. The latest suite of model guidance suggests an upper level ridge will amplify over the Gulf of Alaska on Friday before gradually moving eastward over the weekend. It appears the ridge axis will reach the B.C. coast late Sunday, and then move into western WA early next week while deamplifying. Note a compact upper level low on the eastern periphery of this ridge is set to move through southern B.C. on Sunday, which will bring a 10% chance of light showers to the north Cascades.

The timing of the aforementioned ridge and upper low will bring warmer temperatures on Friday followed by relatively cooler temperatures over the weekend and then warmer temperatures again early next week. Overall model spread for temperatures is fairly low each day, suggesting confidence in the temperature forecast is high. Forecast highs on Friday are generally in the 80s across the lowlands, except 60s at the coast. Highs cool into the 70s for inland valleys over the weekend. Temperatures then warm again Monday into Tuesday as the ridge axis moves over western WA. The NBM 25th-75th percentile suggests highs will likely peak on Tuesday, ranging anywhere from the mid to upper 80s. In fact, highs of 90 degrees or warmer cannot be ruled out on Tuesday for inland valleys; there is currently a 50-70% chance areas to the south and southwest of the Puget Sound will reach 90 degrees or warmer, a 30-50% chance from Kent to Renton to Bellevue, and a 5% chance in Seattle. As such, a moderate HeatRisk returns to the greater Seattle metro area on Tuesday. -23

AVIATION

As the upper level ridge continues to flatten, prevailing west/northwest winds persist. Gusty westerly winds will continue through this evening near the coast as well as in and adjacent to the Strait of Juan de Fuca. Winds begin to ease tonight. VFR conditions are expected in the inland tonight and tomorrow. However, there is a 20-30% chance for broken MVFR ceilings below 3000 feet for the inland terminals due to the marine stratus layer filling along the coast starting tonight. The coastal terminals have a 60-75% chance for ceilings below 3000 ft tonight.

KSEA...VFR conditions are expected through the TAF period. That being said, there is a 20-30% chance for broken MVFR ceilings below 3000 ft between 07-17Z Wednesday. Northerly winds around 10 kts through 08Z tonight. Winds should eventually become light and variable after 08Z Wednesday, before becoming northwesterly near 7-9 kt by 21-22Z Wednesday.

MARINE

Onshore flow continues today into tonight. Northwesterly winds will gust to 25 kts over the coastal waters, with a Small Craft Advisory in effect now through early Thursday morning. Seas will become locally-wind driven and become very steep. Wave heights will increase through tonight, reaching up to 10 to 13 ft with a dominant period of around 10 seconds late Tuesday evening into Tuesday night. Waves in the outermost waters may reach up to 15 ft on Wednesday and Friday.

A Gale Warning remains in effect for the central and eastern waters of the Strait of Juan de Fuca, with gusts up to 40-45 kts expected today associated with a strong marine push. Small Craft Advisory winds will also funnel down into Admiralty Inlet by this afternoon. Marginal Small Craft Advisory wind gusts up to 25 kt are also expected over the west entrance of the Strait of Juan de Fuca Winds this afternoon and evening, mainly to the east of Neah Bay. Winds will ease by late tonight. -23

FIRE WEATHER

The return of low level onshore flow today has eased fire weather concerns west of the Cascades. Elevated fire weather concerns return on Friday and Monday as a warmer and drier airmass will be in place at that time. Minimum relative humidity values are forecast to drop to around 30 percent both days along with some breezy conditions in the afternoon and evening hours. -Felton/23

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 11 PM PDT this evening for West Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning until 11 PM PDT this evening for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 11 PM PDT this evening for Admiralty Inlet.

Small Craft Advisory until 12 AM PDT tonight for Puget Sound and Hood Canal.

Small Craft Advisory until 5 AM PDT Thursday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.