textproduct: Seattle/Tacoma

SYNOPSIS

Cloudy conditions will persist today ahead of an incoming frontal system that will bring lowland rain, mountain snow, and breezy winds to the region on Wednesday. Showers will taper off over the mountains on Thursday before a high pressure ridge brings much warmer and drier conditions over the weekend and into early next week.

SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/

Minor adjustment to the timing in the Winter Winter Advisory (Cascades) otherwise the rest of the forecast remains on track. 33

Previous discussion...Upper level flow will continue to turn southwesterly today as a low pressure system lowers along the British Columbia coast. Clouds will continue to increase today ahead of this incoming system, with potential for light shower activity moving northward later this evening. Temperatures are on track to peak near normal today across the region, with highs in the mid to upper 50s across the lowlands.

As the low pressure system continues to progress southward along the Pacific Coast, the storm system will swing a cold front across western Washington on Wednesday. Winds will ramp up early Wednesday morning, with the strongest wind gusts reaching 35-45 mph along the Pacific Coast, through the Strait of Juan de Fuca, and from Whidbey Island northward across the northern interior. Elsewhere, winds will be breezy, with gusts of 25-35 mph. Winds will remain elevated through the early afternoon before easing throughout the rest of the day. Precipitation will spread inland along the frontal passage Wednesday morning, with steady rain across the lowlands through the afternoon and showers continuing through the evening. The lowlands will see generally 0.25 to 0.75 inches of rainfall through Wednesday night. In addition, snow levels starting at pass level on Wednesday morning will rise to 4000-4500 feet throughout the day before falling below pass level once again early Thursday. This will result in about 4-8 inches of snow accumulation through the Cascade passes, and a Winter Weather Advisory has been issued.

The parent low pressure system will shift inland over Oregon on Thursday, with potential for wrap around moisture to allow for continued light snow over the Cascades. Conditions will dry out across the lowlands on Thursday, with cloudy skies and some afternoon sun breaks. Wednesday and Thursday will see cooler temperatures, with highs peaking in the upper 40s to low 50s across the lowlands.

LONG TERM /FRIDAY THROUGH TUESDAY/

Models remain in good agreement over warmer and drier conditions settling over the western US into the weekend and early next week as a high pressure ridge builds over the region. A weak system may try to overrun the building ridge over the weekend and bring light rain to the north coast, but forecast models continue to trend drier. While there are model differences beyond the weekend, ensembles favor warm and dry conditions into early next week. Temperatures are expected to peak in the low to mid 60s over the weekend away from the immediate coast, with potential for some areas along the Cascade foothills to reach 70 degrees on Monday as warming continues. A pattern change looks to arrive towards the middle of next week, but the details remain uncertain at this time.

15

AVIATION

The next weather system approaches the region tonight and moves into the area early Wednesday. Increasing mid- level clouds move into Western Washington tonight with leading rain and MVFR to local IFR conditions reaching the coast by 10z tonight. Expect the arrival of MVFR ceilings and visibility into the Puget Sound terminals toward 13z with the steadier rain. Surface winds become southerly and increase as the front approaches. Stronger gusts to around 25 kt are more likely for KHQM and KBLI.

KSEA...Increasing mid level clouds through the evening with southerly surface winds. Winds increase to 10-15 kt at the front approaches. Expect lowering ceilings with a 40-50% chance of MVFR ceilings and visibility reductions in rain by 12z through the morning. After the main front pushes through, a return to VFR conditions is favored but scattered showers will bring passing MVFR at times through the afternoon.

MARINE

Surface high pressure continues today with generally light winds over the area waters. A low pressure system will move over the area waters tonight and into Wednesday for increasing southerlies over much of the waters. A Gale Watch has been upgraded to a Gale Warning for higher confidence in gusts exceeding 35 kts over all of the coastal waters. A Gale Warning is also out for the East Entrance, where gusts and sustained will around 30 to 35 kts at times. A small craft advisory has been issued for the Northern Interior Waters and Admiralty inlet for enhanced southerlies.

Broad high pressure will redevelop on Thursday and into Friday, bringing lighter winds and quieter marine conditions.

Coastal seas remaining 3 to 5 feet throughout today. Seas will then build up to 9 to 11 feet Wednesday morning. Seas will remain elevated into Thursday before decreasing on Friday and into the weekend, back down to 3 to 5 feet.

Mazurkiewicz

HYDROLOGY

No river flooding is expected over the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Weather Advisory from 5 AM Wednesday to 11 AM PDT Thursday for Cascades of Pierce and Lewis Counties- Cascades of Snohomish and Northern King Counties-Cascades of Southern King County-Cascades of Whatcom and Skagit Counties.

PZ...Gale Warning from 4 AM to 5 PM PDT Wednesday for East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 4 AM to 5 PM PDT Wednesday for Admiralty Inlet-Northern Inland Waters Including The San Juan Islands.

Gale Warning from 1 AM to 11 AM PDT Wednesday 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.