textproduct: Seattle/Tacoma

UPDATE

Satellite imagery shows low clouds along the coast starting to make their way inland this evening with high clouds over the remainder of the area. Weakening front near 127W at 04Z/8 PM.

No changes to the forecast this evening. Weak onshore flow ahead of the front will push low cloud deck inland overnight. Not good news for eclipse watchers in Western Washington. Not much left of the front as it moves inland Tuesday morning with rain along the coast and just a chance of rain inland. Rain out ahead of the trailing cold front arriving in the afternoon with rain Tuesday night as the front slowly moves through the area. Upper level trough moving through Wednesday keeping precipitation in the forecast. Snow levels around 5000 feet Tuesday only lowering to around 4000 feet Wednesday. Felton

SYNOPSIS

Dry and mild conditions this afternoon will be short-lived, with increasing clouds already ahead of the next disturbance. A frontal system crosses the region tomorrow, bringing a return of lowland rain and mountain snow. Snow levels lower a bit later in the week, with additional weather systems moving through the region and maintaining periods of precipitation.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

After a relatively mild afternoon across most of the region today under mostly clear skies, a change in the weather is in store starting tomorrow. The next front will move through the area Tuesday, with the leading rain arriving at the coast late tonight and pushing east across the region during the day. Snow levels are initially high, around 5000 ft or so, which will limit snow accumulations to the higher Cascade elevations. Some gusty winds near the coast and portions of the interior, with gusts reaching 30 mph in the windiest locations. Snow levels lower a bit Wednesday down to around 3500-4000 ft, allowing for around 6 to 12 inches above 5000 ft and a few inches of snow down the the Cascade passes through Wednesday. Given the current probabilities of advisory amounts at Stevens remaining only 30-40%, and closer to 60% at Paradise and around Mt Baker, will hold off on any winter headline issuance. An advisory may be required for these last two areas if the current trends hold.

Onshore flow will increase Wednesday behind the front, maintaining additional precipitation across the region (especially the mountains) and bringing the potential for the development of a Puget Sound Convergence Zone. With the general instability increasing, there's around a 15% chance for a thunderstorm to develop in the post-frontal air mass, but these are expected to be isolated and infrequent at most - generally just one or two lightning strikes at some point across the region.

LONG TERM /THURSDAY THROUGH MONDAY/

The pattern will remain active as multiple systems look to cross over western Washington throughout the weekend and into early next week. Periods of lowland rain and mountain snow will continue, along with slightly cooler conditions, with high temperatures in the upper 40s and overnight lows in the lower 40s.

AVIATION

Westerly flow aloft becoming southwesterly early Tuesday morning with southwesterly flow aloft continuing through Tuesday. Weak onshore flow in the lower levels.

Vfr ceilings this evening over most of the interior. Stratus deck with 1000-2000 foot ceilings along the coast starting to move inland. The stratus was as far east as Shelton at 04Z. Stratus will continue to move inland with MVFR ceilings over the entire area by 12-15Z. Local IFR ceilings along the coast. Little change throughout the day Tuesday with light precipitation at times.

KSEA...VFR conditions this evening with ceilings lowering to MVFR by 12Z. MVFR ceilings continuing for the rest of Tuesday. Southeast wind 4 to 8 knots becoming southerly 6 to 10 knots after 12z. Felton

MARINE

High pressure continues to break down across the waters, with relatively light winds and small seas given the weak gradients. This break will be short-lived, though, as the next frontal system begins to approach the waters. While the front isn't particularly strong, expect southerly winds to 20 kt with frequent gusts to 25 kt spreading over the coastal waters early Tuesday. Chances for gusty southerly winds over the east entrance and extending south over the northern half of the Puget Sound zone remain lower, around 40% or so, so will hold off on any headlines there. Meanwhile over the coastal waters, expect the seas to be quite choppy as short period waves build; the winds aren't strong enough or long duration enough to build much higher than 6 ft, but with dominant periods 6 to 7 seconds it will be rough.

Additional advisories may be needed with west winds increasing through the Strait on Wednesday, and also later in the week for the coastal waters as seas build further to around 11 ft late Wednesday through Thursday. After a briefly subsiding, another west swell is likely to arrive over the weekend again pushing seas above 10 ft.

Cullen

HYDROLOGY

No river flooding is expected during the next seven days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 1 AM PST 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-West Entrance U.S. Waters Strait Of Juan De Fuca.