textproduct: Seattle/Tacoma

SYNOPSIS

Weak upper level trough moving through late tonight into Monday morning. Puget Sound convergence zone developing tonight and remaining into Monday. Strong front approaching the area Tuesday moving through Tuesday night. Heavy snow possible in the Cascades Tuesday night. Cool upper level low behind the front Wednesday and Wednesday night. Drying northerly flow aloft behind the low Thursday and Friday. Splitting system arriving late in the weekend.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

Satellite imagery shows mostly cloudy skies over Western Washington. Doppler radar has a few showers in the South Cascades. Temperatures at 3 pm/22z in the lower to mid 50s.

Clouds starting to bubble up late this afternoon but with plenty of cloud cover will be hard to generate enough surface heating to create much in the way of shower activity this evening. Surface gradients turned onshore this afternoon with onshore flow increasing tonight. A Puget Sound convergence zone will develop mostly likely over King county tonight with the convergence zone drifting north early Monday morning. Weak upper level trough also arriving overnight increasing the shower chances outside of the convergence zone. Lows in the 40s.

Weak upper level trough moving through Monday morning. Convergence zone over Snohomish county weakening and moving into the foothills. Low level onshore keeping skies at least mostly cloudy. Highs in the lower to mid 50s.

Upper level low and frontal system moving out of the Gulf of Alaska Monday night into Tuesday morning. Warm front brushing the north coast late Monday night. Cloud cover will keep lows in the lower to mid 40s.

Strong cold front approaching Tuesday with the front still offshore late Tuesday afternoon. Rain starting on the coast in the morning spreading inland in the afternoon. Winds picking up along the coast in the afternoon. Cool with highs near 50.

Have issued a winter storm watch beginning late Tuesday afternoon for the Cascades. Snow level near 3000 feet with heavy snow possible Tuesday night ahead and with the front. Breezy/windy conditions developing with the front for the lowlands. Strongest winds along the coast and over the Northwest Interior. Felton

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Cool upper level low behind the front over Western Washington Wednesday moving east Wednesday night. Snow levels could get as low as 1500 feet. Winter storm watch continuing for the Cascades into Wednesday night for additional significant snow accumulations.

Drying northwesterly flow aloft behind the upper level low Thursday and Friday. Very cool mornings both Thursday and Friday with the colder locations getting below freezing. Frost advisories will likely be needed especially Thursday morning.

Weak upper level ridge moving through Saturday ahead of a splitting front Sunday.

AVIATION

Ceilings have been slow to improve today as MVFR has continue to linger in the afternoon. A brief spell of VFR cigs are expected to rebound for terminals along the I-5 corridor. However, MVFR/IFR are slated to redevelop this evening and maintain tonight area-wide. For Puget Sound airfields, a convergence zone looks to develop around 03- 06z and may even bring LIFR cigs to KPAE as well. MVFR to areas of LIFR are forecast to linger into Monday as well.

KSEA...MVFR currently at the terminal as cigs have been slow to improve. A brief reprieve to VFR is possible between 22z-03z. However, a models have a PSCZ forming over the airfield with the return of MVFR/IFR cigs and possible vis reductions. Winds SW this 4 to 8 knots this evening, then increasing to 8-12 kt with gusts up to 20 kt Monday morning. MVFR/IFR cigs are to remain into Monday as well.

McMillian

MARINE

Surface low pressure just off the N CA coast as a high pressure system develops offshore in the northeastern Pacific. Onshore flow is increasing as a small craft advisory remains in effect for westerlies down the Strait of Juan de Fuca this evening and likely well into Monday. A stronger frontal system arriving late Tuesday into Wednesday will likely yield more widespread headlines as we will see increased winds and seas and possible gales through the strait. Surface high pressure looks to rebuild across the region towards the second half of the week.

Coastal seas 4 to 6 feet throughout the weekend. Seas will then start to build upwards to 8 to 10 feet by Tuesday evening and remaining elevated through Thursday.

McMillian

HYDROLOGY

No river flooding the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Winter Storm Watch from Tuesday afternoon through late Wednesday night 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...Small Craft Advisory until 6 PM PDT Monday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.