textproduct: Seattle/Tacoma

SYNOPSIS

An upper level ridge will gradually build across the Pacific Northwest early this week, resulting in warming temperatures through Tuesday. Temperatures will peak on Tuesday, resulting in Minor to Moderate HeatRisk. Onshore flow increases Wednesday as the upper ridge weakens. The next disturbance approaches Western Washington later in the week.

SHORT TERM /TONIGHT THROUGH TUESDAY/

Mainly clear conditions this evening as high pressure builds into the Pacific Northwest. Upper ridging will continue to gradually build over the region on Monday with temperatures warming further into the 70s and low 80s by Monday afternoon.

Light offshore flow late Monday into Tuesday with a weak surface thermal trough developing early this week. Temperatures will peak on Tuesday with the upper level ridge axis overhead. Temperatures Tuesday afternoon will reach the 80s for most lowland areas, with the potential for highs in the low 90s across portions of Lewis, Mason, Thurston, and Grays Harbor Counties. These temperatures correspond to widespread Minor HeatRisk, as well as a 50-80% probability for Moderate HeatRisk from Everett southwards across Puget Sound and towards the Chehalis Valley. If you're heading out on the water, always wear a life jacket and take precautions as lakes and rivers continue to run cold.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/

Onshore flow increases by Wednesday as the upper ridge axis slides eastwards and the ridge flattens over Western Washington. This will result in increasing clouds Wednesday, as well as cooler temperatures, with highs back into the 60s and 70s. Of note, there is a slight uptick in precipitation potential Wednesday afternoon into the evening across the Cascades as a weakening upper low approaches Western Washington. NBM probability for thunderstorms on Wednesday afternoon ranges 10 to 20% at this time over the Cascades.

Onshore flow continues on Thursday with a continued cooling trend, with current forecast highs dropping back into the 60s to low 70s. Light precipitation or drizzle also can't be ruled out on Thursday as well. Ensembles are consistent that deep troughing approaches the Pacific Northwest from the NE Pacific Friday into next weekend. Unsettled conditions, including precipitation chances, clouds, and cooler temperatures are expected by next weekend with the troughing across the area. JD

AVIATION

Northerly flow aloft continues into Monday as an upper ridge continues to build offshore. VFR conditions prevail through the TAF period with mostly clear skies. High clouds will increase Monday afternoon. N/NW surface winds of 5 to 10 kts this evening will become light NE for most sites tonight. N/NW surface winds increase again on Monday.

KSEA...VFR conditions through the TAF period with increasing high clouds Monday afternoon. N/NW surface winds ranging 7 to 12 kts transitioning more NE around 5 to 9 kts tonight. JD/18

MARINE

High pressure continues to build across the waters today with Northwest flow prevailing over the Coastal Waters into tonight. Northwest winds will briefly be enhanced this evening over the Coastal Waters, with sustained winds ranging 15 to 20 kts and gusts to 25 kt. In addition, increasing west winds are expected through the Strait of Juan de Fuca this evening. While sustained winds will generally fall into the 10-20 kt range, gusts up to 25 kts look frequent enough from afternoon obs to warrant an SCA until at least late tonight/early Monday morning. Will continue to monitor to see if this trend persists tonight.

Winds will become lighter Monday into Tuesday as a weak thermal trough develops along the coast, briefly turning winds offshore Monday night into early Tuesday. Onshore flow resumes late Tuesday as the thermal trough is shifted eastwards. Onshore flow will further strengthen Wednesday and through the rest of the weak as weak disturbances move across the waters. Small Craft Advisory winds are likely for an extended period beginning Wednesday through late in the week in the Strait of Juan de Fuca. There also remains a 30 to 60 percent chance of gales through the central and eastern Strait Thursday evening.

Seas will build to 6 to 10 feet for a brief period later today into tonight. Seas will be steep during this time with a dominant period of 6 to 7 seconds. Seas will fall back to 4 to 6 feet Monday and Tuesday. Seas will generally remain 4 to 6 feet through late week, building to 8 feet at times. JD/18

FIRE WEATHER

An upper ridge will setup a dry, warm pattern on Monday and Tuesday. Maximum temperatures will reach the 80s (with low 90s in localized areas) on Tuesday. A weak thermal trough will build north over the region, which results in light offshore developing late Monday into Tuesday. Winds will be rather light during this period, however, a few gusts ranging 15 to 20 MPH will remain possible over the Cascades. Minimum RHs will approach critical thresholds on Tuesday with the light offshore flow, with RHs dropping into the 20% range mainly from King County southwards, and into the Cascade Valleys. However, this stretch will be short-lived as onshore flow resumes Wednesday resulting in higher humidities 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 midnight PDT tonight for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 2 AM PDT Monday 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.