textproduct: Seattle/Tacoma

SYNOPSIS

Slowly exiting low pressure will move southeastward tonight, allowing showers to come to an end tonight. High pressure building overhead brings drier conditions and near-normal temperatures into early next week. Cooler and unsettled conditions may return mid-week as series of systems move inland aimed at Vancouver Island. High pressure will return by the end of the week, allowing for drier and warmer conditions Thursday and Friday.

SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/

Current radar showing only a few blobs of precip left over W WA this evening over central and eastern portions of King and Pierce counties. Satellite shows clouds lingering over the east and south Sound areas while western Whatcom and Skagit counties as well as much of the coast seeing clear skies. Low level moisture may still result in isolated patches of fog, especially in the more prone areas of the SW interior. All that said, inherited forecast remains on track and no evening updates are required. For further forecast details, please refer to the Previous Discussion section below. 18

From Previous Discussion...A low pressure system will slowly meander southeastward into Sunday, with wrap around moisture maintaining light shower activity across the Pacific Northwest through the evening. Most areas across western Washington will see high temperatures shy of 60 degrees today. As the upper low moves southeastward, dry northeast flow aloft filling in behind will bring in cooler air with lows expected to dip into the mid 30s to mid 40s. This will likely allow frost to form early Sunday morning for portions of the southern Cascade foothills and valleys and areas south of the Olympics, and a Frost Advisory remains in effect for Sunday morning.

Weak ridging will build into British Columbia on Sunday with continued dry northeast flow aloft over western Washington, bringing slightly warmer daytime temperatures in the mid 50s to lower 60s. Skies will be mostly clear Sunday into Sunday night, with even cooler overnight temperatures generally in the 30s for most areas. Frost will likely be more widespread early Monday morning, and a Frost Advisory remains in effect for most areas south of Seattle and along the Hood Canal and North Coast for Monday morning.

The upper level ridge axis over British Columbia will shift southward over the Pacific Northwest on Monday, bringing more warming to the region. Highs will peak near normal under sunny skies, reaching the upper 50s to mid 60s.

LONG TERM /TUESDAY THROUGH SATURDAY/

Cloud cover will increase over western Washington on Tuesday as a weak atmospheric river brings ample moisture to British Columbia. While the majority of the precipitation is expected to stay north, chances for rain increase on Tuesday along the coast and over higher terrain. The decaying atmospheric river system is set to shift southward late Tuesday into Wednesday, bringing increasing chances for rain across western Washington. However, the path of the atmospheric river remains fairly uncertain at this time, with many ensemble members keeping western Washington on the dry side.

A high pressure ridge will then build into the Pacific Northwest on Thursday as another atmospheric river system traverses well to the north. This will bring a few days of warming and drying, with low level offshore flow and highs reaching the lower 70s by Friday. Some uncertainty remains over how long the high pressure will remain in place, with potential for troughing to break down the ridge by the weekend and bring in some more rainfall and cooler temperatures.

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AVIATION

VFR conditions favored this evening and tomorrow. Scattered showers will subside this evening. Fog may form Sunday morning, with the highest chances of seeing LIFR conditions in the southern interior and mountain valleys. Northerly winds trending lighter overnight. Breezy conditions expected again Sunday afternoon across Puget Sound and northern interior with winds 8-12 kt and gusts 20-25 kt.

KSEA...VFR conditions tonight and tomorrow. Northerlies easing late this evening to 2-5 kt. Northerly winds will increase again Sunday afternoon to 8-11 kt and gusts to 20 kt. Fog may form near the terminal, but not expected to bring direct impacts to the terminal.

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MARINE

High pressure building over the interior of British Columbia will lead to increasing northerly or offshore flow tonight into Sunday. This will result in enhanced winds over the Northern Inland Waters near the San Juan Islands, for which a Small Craft Advisory has been issued. Additionally northerly winds will increase across Puget Sound Sunday afternoon, with the 70-80% possibility for wind gusts to exceed 21 kt. Winds will ease early next week as high pressure over British Columbia weakens and broad surface ridging remaining offshore. A weak frontal system will move across the waters late Tuesday night into Wednesday.

Seas will hover around 6-9 feet this weekend, decreasing to 4-6 feet early next week. Seas will briefly build on Wednesday but will remain below 10 feet.

29/27/41

SEW WATCHES/WARNINGS/ADVISORIES

WA...Frost Advisory from midnight tonight to 8 AM PDT Sunday for Foothills and Valleys of Pierce and Southern King Counties-Foothills and Valleys of Thurston and Lewis Counties-Middle Chehalis River Valley.

Frost Advisory from midnight Sunday night 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...Small Craft Advisory until 5 AM PDT Sunday for Northern Inland Waters Including The San Juan Islands.