textproduct: Seattle/Tacoma

SYNOPSIS

An upper level ridge will slowly build across the Pacific Northwest this weekend, resulting in a gradual warming trend into early next week. Temperatures will peak on Tuesday, resulting in Minor to Moderate HeatRisk. Onshore flow will increase Wednesday with upper troughing approaching Western Washington late in the week.

SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/

A mix of clouds and sunshine this afternoon with continued weak onshore flow across Western Washington. Temperatures remain relatively cool today, with highs in the upper 50s to mid 60s.

Upper level ridging will gradual build into Western Washington beginning Sunday and continuing into early next week. This will result in a warming trend across the area. Highs on Sunday will peak in the 60s to low 70s, with Monday afternoon temperatures reaching the 70s, with low 80s south of Olympia and near interior Grays Harbor County. An upper level low located over Montana on Monday will also spread high clouds into Western Washington, particularly during the afternoon.

LONG TERM /TUESDAY THROUGH SATURDAY/

The upper ridge will remain situated over Western Washington on Tuesday before the ridge begins to flatten midweek. A brief thermal trough will build into the region on Tuesday, which results in Tuesday being the warmest day of the week with light offshore flow. Widespread highs in the upper 70s to mid 80s are expected. The potential for low 90s Tuesday afternoon will also exist from Olympia southwards and into interior Grays Harbor and Mason Counties. Widespread Minor to Moderate HeatRisk will exist on Tuesday. Despite the warm air temperatures, rivers and lakes remain cold. If you're heading out on the water, always wear a life jacket and take precautions for the cold water. In addition to the warm temperatures, daytime RH values will dip between 20 to 30% with light east flow - see fire weather section for more details.

Ensembles are generally consistent in the upper ridge slowly flattening by Wednesday, resulting in increasing onshore flow. Temperatures will cool by midweek, with forecast high temperatures on Wednesday in the 60s and 70s. Onshore flow will continue on Thursday. Ensembles begin to show a deeper trough developing across British Columbia by late next week into the following weekend. There is a notable uptick in POPs by late Friday into Saturday with the upper troughing, in addition to cooler temperatures next weekend. JD

AVIATION

Upper level troughing over the northeastern Pacific will maintain southwesterly flow aloft through tonight. Flow aloft will then become more westerly, then northwesterly into Sunday as an upper level ridge starts to build offshore. Onshore flow continues in the low levels, but will weaken into Sunday.

Conditions have rebounded to VFR for all TAF sites this afternoon as morning cloud cover continues to scatter. Winds for the majority of the interior terminals have shifted to the N/NE and primarily persist at 5-10 kt this afternoon. The strongest winds are at KHQM and KCLM, where winds are breezy to 25 kt at times out of the W/NW. Winds will ease areawide again during the overnight period, but will increase again Sunday afternoon and evening, primarily out of the N. Areas of stratus may redevelop into early Sunday, but expect overall conditions to remain VFR at the area TAF sites.

KSEA...VFR conditions with scattered clouds between 3000-4000 ft this afternoon. VFR conditions are expected to prevail throughout the TAF period, with some additional scattered cloud cover possible at the terminal Sunday morning. Winds are out of the NE at 5-10 kt this afternoon. Northerly winds will ease again overnight to 5 kt or less, but will shift to the NW and increase to 8-12 kt Sunday afternoon.

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MARINE

Small craft advisory strength westerlies will persist across the central and eastern Strait of Juan de Fuca tonight into early Sunday morning before easing. The increased onshore flow will also bring gusty northwesterly winds to 25 kt to Admiralty Inlet at times tonight. Winds will then ease across the majority of the area waters on Sunday as high pressure builds across the coastal waters, though portions of the coastal waters will see an increase of northwesterly winds which could approach small craft criteria at times Sunday afternoon and evening. This pattern will also allow for waves to rise and steepen to 7-9 ft at a period of around 7-9 seconds. Winds will gradually ease and waves will subside towards 5-7 ft heading into Monday as high pressure weakens over the region. A thermal trough then looks to develop along the coast Monday night into Tuesday, which will bring a brief period of offshore flow to the area waters- but will not be strong enough to have any significant marine impacts.

A frontal system will then move across the area waters Wednesday into Thursday, resulting in the return of onshore flow. Additional headlines will be likely for the central and eastern Strait of Juan de Fuca as onshore flow increases Wednesday night. Seas will primarily range between 6-8 ft.

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FIRE WEATHER

An upper ridge will result in a drier pattern Monday and Tuesday with maximum temperatures reaching the 80s (and a few spots in the low 90s) by Tuesday. Light offshore flow is expected late Monday into Tuesday as a brief thermal trough develops. At this time, winds are not expected to be strong, however, a few locations within the Cascades could see gusts in excess of 20 MPH. In addition, minimum RH values will lower into the 20 to 35 percent range for most locations away from the water. However, this stretch of warm, dry conditions will be short-lived as onshore flow resumes by Wednesday bringing higher RHs for the second half of the week.

HYDROLOGY

The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated during this time as needed.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 7 AM PDT Sunday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 5 AM PDT Sunday for Admiralty Inlet.