textproduct: Seattle/Tacoma

SYNOPSIS

Surface high pressure weakening today. Zonal flow aloft. Next system moving down British Columbia coast moving through the area Tuesday. Post frontal convergence zone Tuesday evening. High pressure, both surface and aloft, rebuilding Wednesday. Upper level ridge remaining over the area through the weekend. Thermally induced surface trough moving up the Oregon coast reaching the Washington coast Saturday turning the low level flow offshore. Surface trough moving inland Sunday.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Satellite imagery shows high clouds along the coast and over the Northwest Interior early this morning. Patchy fog forming in the Southwest Interior with visibility at Chehalis down to a half mile. Temperatures at 3 am/10Z were in the upper 30s and 40s.

Next system to move into Western Washington currently near Haida Gwaii and slowly moving southeast. High clouds out ahead of the system will spread over the remainder of the area this morning into the afternoon hours. Chance of rain by late afternoon along the north coast. Highs in the 60s.

Front continuing to slowly move southeast tonight. By 12z Tuesday front still north of the area. Surface pressure gradients tightening up over the Northwest Interior as the front approaches. Have issued a wind advisory for the Northwest Interior and the San Juans beginning at 2 am Tuesday morning for southeast winds increasing to 20 to 30 mph with gusts 40 to 45 mph. Rain out ahead of the front reaching the north coast and Northwest Interior by midnight. Chance of rain as far south as Olympia by early Tuesday morning. With the cloud cover lows will be much warmer than the previous mornings, in the lower to mid 50s.

Front slowly moving through Western Washington Tuesday. Rain over most of the area by mid morning. Front moving through the Northwest Interior and north coast early afternoon. Winds easing behind the front. Highs in the lower to mid 60s.

Front moving through the remainder of the area by early in the evening with rain coming to an end. Post frontal convergence zone over Snohomish county will dissipate after midnight. Not much in the way of cool air behind the front with just limited shower activity outside the convergence zone. Lows in the mid 40s to lower 50s.

High pressure, both surface and aloft, building over Western Washington Wednesday. Winds easing overnight. Patchy fog developing early in the morning. What little fog that does form will be gone by mid morning. Skies clearing with plenty of sunshine especially in the afternoon. Highs in the lower to mid 60s. Felton

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

Extended models have finally gotten rid of the slight chance pops for Thursday and Friday. Upper level ridge over the area with high pressure at the surface. Thermally induced surface trough moving up the Oregon coast Friday extending north to the Washington coast Saturday. Low level flow turning offshore. In this scenario this time of year it is not uncommon for the coast to be the warmest location in Western Washington. Thermally induced surface trough moving inland Sunday making it the warmest day for the interior. Lows in the 40s Thursday morning, mid 40s to lower 50s Friday through Sunday morning. Highs in the mid to upper 60s Thursday and Friday, 60s and lower 70s Saturday and Sunday.

Even with the normal high in Seattle starting October at 66 degrees, the normal number of 70 degree plus in Seattle in October is only 2. Out of the 170 days total ( in 81 years of records ), 51 ( 30 percent ) are 75 degrees or warmer. 75 percent of the 70 degree plus days in October have occurred in the first 10 days of the month and all of the 75 degree plus days have occurred in the first 16 days of the month. Felton

AVIATION

Zonal flow aloft with occasional shifts to the NW at times today, strengthening tonight as gradients tighten. Light and variable surface winds this morning becoming southerly 5-10 kt this afternoon in advance of approaching front. Speeds increase further this evening and overnight generally ranging 10-15 kt with gusts up to 20 kt possible.

Widespread VFR conditions in place this early morning with isolated patches of MVFR to IFR conditions due to lingering low-level moisture. Cigs expected to lower throughout the day as incoming front approaches, however VFR expected to persist for the majority of the TAF period for most terminals. Western-most terminals will begin to encroach on MVFR conditions this evening between 03-06Z while remaining terminals likely will not see these conditions emerge until around 12Z Tuesday. Similarly, inclusion of precip will likely be needed for 12Z issuance for western terminals while eastern ones likely hold off until 12Z or just a little after, thus falling outside current forecast window.

KSEA...VFR conditions for nearly the entire period even though cigs will gradually fall throughout the day. MVFR conditions expected to develop near the end of the TAF period, around 10-12Z, as front draws nearer. Start of precip also expected during this time frame. Light and variable winds this morning before turning more southerly at 5-10 kt this afternoon. SW winds 10-15 kt with gusts up to 20 kt after 03Z tonight with best chances for gusts holding off until the 10-12Z time frame.

18

MARINE

The next frontal system arrives Tuesday with increasing southerly winds over all waters - Small Craft Advisories are in effect for most waters, although it appears the Northern Inland Waters run a good chance for consistent gusts exceeding Gale criteria. As such, have upgraded the SCA there to a Gale Warning. Winds will turn more westerly through the Strait Tuesday afternoon. Meanwhile, expect elevated seas with swells reaching 10-11 ft. Onshore flow will ease late Tuesday night. The flow will then turn offshore on Wednesday with a thermal trough along the coast. Light offshore flow continues through the end of the week. 18/33

SEW WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory from 2 AM to 2 PM PDT Tuesday for Lowlands of Western Whatcom County-San Juan County.

PZ...Small Craft Advisory from 5 PM this afternoon to 5 PM PDT Tuesday for Admiralty Inlet-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-Puget Sound and Hood Canal-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning from 11 PM this evening to 5 PM PDT Tuesday for Northern Inland Waters Including The San Juan Islands.