textproduct: Seattle/Tacoma

SYNOPSIS

Drier conditions are expected over the weekend as an upper low offshore weakens and moves inland well to the south of the region. An upper level ridge moving into the region on Sunday will keep conditions dry and temperatures seasonable across western Washington into Monday. The first half of next week will remain mostly dry, with chances of precipitation increasing mid to late week as a series of systems approaches the Pacific Northwest.

SHORT TERM /TODAY THROUGH MONDAY/

An upper level low offshore will continue to bring showers and some isolated thunderstorms to the coastal waters through the early morning hours. Showers will gradually taper across the waters through the day as the low weakens and exits the area. Otherwise, expect cool conditions for areas across the interior this morning as skies continue to clear. Morning lows are expected to approach freezing for many areas south of the Sound, but particularly across the Chehalis River Valley. Areas of clearing have also started to see some fog development overnight, so could even see some spots of dense fog this morning. Morning temperatures will remain a couple degrees warmer for areas north of Seattle- however, with temperatures expected to dip into the mid 30s, could see some areas of frost development as well. Freeze warnings remain in effect for areas along the Chehalis River Valley and frost advisories remain in effect for areas north of Seattle and along the foothills of the Cascades through mid morning. Any areas of fog are expected to scatter by late morning.

Overall conditions will be drier today and Sunday as the low offshore exits the area and an upper level ridge moves into the region. Cool overnight lows in the 30s will bring areas of additional frost development to the area on Sunday morning and moisture in the low levels will likely promote another round of fog development. High temperatures will be in the low to mid 50s both days.

The upper level ridge axis will push further inland on Monday, maintaining mostly dry conditions for western Washington for the start of next week. A few ensemble members do continue to hint at a weak frontal system brushing the region, which may bring some light precipitation chances (roughly 20 to 30%) to the coast through the day. Morning lows will be in the 30s and afternoon highs will be in the low to mid 50s.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Conditions largely look to remain drier through the first part of next week, though a splitting system may bring some light rain to portions of the area on Tuesday. A return to a more unsettled pattern looks more favorable mid to late week as a series of systems approaches western Washington. At this time, a weak system looks to move across the area on Wednesday, with a stronger system on Friday looking to bring more notable chances of precipitation. However, it is worth noting that there still remains a decent spread amongst ensemble solutions for the second half of the week. Morning lows will be in the mid 30s to mid 40s and afternoon highs will be in the mid to upper 50s throughout the period.

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AVIATION

Surface low pressure will continue to dig southward off the shore, with high pressure rebuilding in southern B.C. over the weekend. Showers with isolated thunderstorms will continue over the coastal waters through the morning. Remaining interior terminals will dry out today. The clear skies in the interior has led to areas of frost and/or fog this morning. The densest fog has been concentrated in the south sound/south interior with quarter mile visibilities from Shelton to Chehalis. Additional areas of fog and mist are present north of this and will linger through roughly 18Z as high clouds linger through the day. Additional fog/mist development tonight is likely, and may be more widespread in coverage in the Puget Sound/south interior. Light northeast to southeast winds at 5 kt or less will prevail.

KSEA...Conditions drying out today. A patch of mist/fog has developed to the east of the terminal near Renton, and north near BFI. With winds remaining calm or light out of the east, the lowest visibilities will likely remain outside of the terminal, though there remains the potential for some of it to spread close to SeaTac this morning through 18Z. High clouds will pass through the day with another round of fog appearing more likely tonight/Sunday morning.

HPR

MARINE

A surface low will begin to dig southward across the waters today. High pressure will rebuild inland. This will lead to a brief window of offshore flow through the weekend, with gustier winds to 20 kt this morning in the coastal waters diminishing quickly. Shower and thunderstorm activity will continue in the coastal waters through the morning, but will wind down through the day. Hazardous winds are not expected at this time through Wednesday, when the next system passes through. Another system may also skirt the waters late next week/weekend.

Seas will hover at 4-6 ft through the weekend, but build back to 10 to 11 ft Monday as swells increase out of the west. Seas drop back down to 6-8 ft Tuesday through Thursday but build back to 10-14 ft late Thursday through next weekend.

HPR

SEW WATCHES/WARNINGS/ADVISORIES

WA...Frost Advisory until 9 AM PDT this morning for Downtown Everett / Marysville Area-Eastern Kitsap County-Eastern Strait of Juan de Fuca-Eastside-Foothills and Valleys of Central King County-Foothills and Valleys of Snohomish and Northern King Counties-Foothills and Valleys of the North Cascades-Lake Crescent Area Including US 101- Lowlands of Western Skagit and Northwestern Snohomish Counties-Lowlands of Western Whatcom County-Shoreline / Lynnwood / South Everett Area-Western Strait of Juan de Fuca.

Freeze Warning until 9 AM PDT this morning for Lowlands of Lewis and Southern Thurston Counties-Middle Chehalis River Valley.

PZ...None.