textproduct: Seattle/Tacoma

SYNOPSIS

Dry northeasterly flow will maintain clear skies with morning frost and fog possible Monday morning. Temperatures return to near-normal early in the week. Chances for rain mid-week as a weak atmospheric river aimed at British Columbia sinks southward. Upper level ridging brings warm and dry conditions for the second half of the week before cooler and unsettled conditions possibly return this weekend as a weather system approaches the Pacific Northwest.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

Mostly clear skies over W WA this evening although some clouds still present over the Cascades. Temps mostly in the lower 50s although some high 40s are starting to pop up. This lines up well with the expectation for some brisk and chilly temperatures to start Monday morning. That said, inherited Frost Advisory looks on track and current forecast products do not look like they need any updating at this time. For additional forecast details, please refer to the Previous Discussion section below. 18

From Previous Discussion...Dry northeasterly flow aloft in the wake of an exiting upper level low will continue to promote clear skies, allowing daytime temperatures to reach a few degrees above yesterday. Highs today are on track to top out in the upper 50s to lower 60s, generally a degree or two shy of seasonal normals. Clear skies tonight will continue to promote colder overnight lows, with weak winds allowing for the formation of frost and patchy fog in the early morning hours. A Frost Advisory remains in effect through Monday morning for much of the Puget Sound area southward, the Hood Canal, and the North Coast to signal the end of the growing season in these areas. Continued dry northeasterly flow will allow for slightly warmer temperatures on Monday, with most inland areas surpassing 60 degrees.

As a weak atmospheric river takes aim at British Columbia, the influx of moisture will bring increased clouds over western Washington Monday night, potentially limiting fog and frost development early Tuesday morning. While most of the rainfall with this system is expected to stay north of the Canada border, rain may clip the northwestern Olympic Peninsula and northern interior on Tuesday. Temperatures will stay fairly steady into Tuesday, with most inland areas once again seeing highs near or above 60 degrees.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

The decaying atmospheric river system will shift slightly southward on Wednesday, but an upper level ridge building along the southwestern Pacific Coast may keep most of the region on the dry side. Chances for rain will be highest once again over the Olympic Peninsula and northern Interior, though the forecasted path of the atmospheric river may shift as the event draws closer. The upper level ridge will continue to build northward into western Washington on Thursday and Friday, though the warming and drying trend may begin as early as Wednesday. Temperatures will rise well above normal, with highs set to reach the upper 60s to lower 70s by Friday. Some areas in the Cascade valleys including the Highway 12 corridor may even see highs in the upper 70s. However, no daily temperature records are expected to be broken, as October 16th was one of the warmest October days on record in 2022 at 88 degrees in Seattle.

By Saturday, the upper level ridge is expected to be well to the east as troughing develops over the Pacific Northwest. This will likely bring in chances for rain and cooler temperatures, though the exact details remain uncertain at this time.

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MARINE

Winds will ease this evening across the Northern Inland Waters and Puget Sound as high pressure settled over British Columbia weakens today. Broad high pressure over the Pacific will expand into area waters on Monday and strengthen late in the week. A weak front will move across the waters late Tuesday into Wednesday with little to no impacts. Seas generally 5-8 feet into next week, and may get steep at times early in the week.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Frost Advisory from midnight tonight to 8 AM PDT Monday for Eastern Kitsap County-Foothills and Valleys of Pierce and Southern King Counties-Foothills and Valleys of Thurston and Lewis Counties-Foothills of the Western and Southern Olympic Peninsula-Lake Crescent Area Including US 101- Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King Counties-Middle Chehalis River Valley-Northern Hood Canal-Northern Washington Coast-Olympia and Southern Puget Sound-Southern Hood Canal-Willapa and Black Hills.

PZ...None.