textproduct: Seattle/Tacoma

UPDATE

No changes to the overall foreacast. Please see the aviation and hyrdology sections below for updates to those forecasts. |

SYNOPSIS

Weak system moving through Western Washington this afternoon and evening. Much stronger system arrives Friday with rain and windy conditions beginning Thursday night ahead of the front. Another strong system moving quickly east will reach the area Saturday for another round of rain and wind. Cooler air mass behind the front could drop snow levels below all of the passes Sunday. The active pattern will continue into next week.

SHORT TERM /TODAY THROUGH FRIDAY/

Satellite imagery shows clear skies over Western Washington. Fog has formed in the Central and Southern Puget Sound as well as along the Strait of Juan de Fuca in the last couple of hours. Temperatures at 3 am/10z were mostly in the 40s with the colder locations in the mid to upper 30s.

Surface gradients increasing as a weakening front approaches Western Washington this morning. This will stir things up enough to dissipate the shallow fog layer. Rain arriving on the coast midday with the rain spreading inland mid afternoon. The front by this point will not have much left to it so only expecting a brief, 2 or 3 hours, of rain just ahead of the front. A little push of warmer air ahead of the front will get some locations into the lower 60s with the remainder of the area in the upper 50s.

Front moving through the Puget Sound area early evening and into the Cascades well before midnight. Satellite imagery showing nothing in the way of cooler air behind the front making for little post frontal shower activity. Cloud cover overnight keeping lows in the mid to upper 40s.

Thursday now looking like a dry day especially for the southern portion of the interior. Frontal system approaching the coast Thursday afternoon with the leading warm front weakening and moving into Southern British Columbia in the afternoon. This puts Western Washington in the warm sector and with the weakening warm front just some middle levels clouds over most of the area. Could still see a brief shower out of the middle level deck. The best chance for a little rain will be along the North Coast. Highs Thursday in the lower to mid 60s.

Trailing cold front slowing down Thursday night as the upper level trough behind the front digs south between 130-135W. Winds picking up overnight along the coast and in the Northwest Interior with gusts in the 40 to 45 mph range likely. Rain will be slow to arrive with the slowing front. Rain not getting east of Puget Sound until after midnight. Lows a couple of degrees either side of 50.

Upper level trough continuing to dig offshore which will stall the front over Western Washington Friday making for a wet and windy day. Jet aimed into the Central Oregon Coast and models show highest IVT values south of the area so even though the front will stall Western Washington will not get the highest rainfall amounts out of this system. In general a half to an inch of rain over the interior with one to two ( maybe 2.5 inches far North Coast ) along the coast and in the Cascades. Heaviest rainfall will be in the Olympics with 2 to 4 inches possible. Snow levels generally in the 6000-7000 foot range making the precipitation rain in all the passes.

Front moving through Friday evening with rain turning to showers and winds easing. Felton

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

Models having trouble with the placement of the next system. This front has a developing surface low near 990 mb. Will have to keep an eye on this one with a few of the ensemble solutions showing the potential for high winds along the coast Saturday into Saturday night and over the interior Saturday night into Sunday morning. Another round of rain will accompany this feature. Snow levels dropping below the higher passes Saturday into Saturday night with the potential for snow levels to be below all of the passes by Sunday morning. Nothing organized moving into Western Washington Sunday but cool upper level trough will produce plenty of showers dropping a few inches of snow above 3000 feet. While the operational runs show a bit of a break Monday the ensemble solutions tell a different story keeping likely pops in the forecast. Solutions become very inconsistent Tuesday making for a low confidence forecast. Felton

AVIATION

Southwest flow aloft will increase as a weak front moves onshore and dissipates this evening. The low level flow turning southerly this morning. Light surface flow and surface based inversions have led to the formation of LIFR fog and stratus across all terminals this morning with the exception of HQM. The low clouds will erode around mid-day as high and mid level clouds begin to increase ahead the approaching front. Ceilings will lower to MVFR in light rain along the coast late this afternoon with said conditions spreading to interior areas mainly north of KSEA by this evening.

KSEA...LIFR fog/stratus will remain at terminal through mid-day. A combination of increasing southerly wind and increasing high level clouds should help erode the low clouds around 18z. VFR and increasing mid to high clouds are expected thereafter with a few showers by early evening, but most precipitation with this system is expected to remain north and west of terminal. Surface winds light and variable becoming southerly and rising to 8 to 12 knots toward midday.

McMillian

MARINE

A weak system will move through the waters this afternoon and evening. A stronger frontal system will arrive Thursday night into Friday. A developing surface low near 990 mb will reach the offshore waters late Friday night and move into Vancouver Island later Saturday. The associated front will move through the waters Saturday night. The pattern will remain active into next week.

Gale watch in effect for Thursday afternoon into Friday morning for the coastal waters as well as the entrances to the Strait of Juan de Fuca, Admiralty Inlet and the Northern Inland waters. The system arriving Saturday has the potential to produce gale force winds over all the waters. Winds easing the latter half of the weekend into Monday.

Seas 8 to 10 feet today subsiding a little tonight then building to 10 to 14 feet Thursday and as high as 20 feet Thursday night. Seas subsiding slowly Friday into Saturday ending up around 10 to 13 feet Sunday. Felton

HYDROLOGY

Even with the two to four inches of rain forecast for the Olympics later Thursday night through Friday the flooding risk on the Skokomish River continues to diminish. Other river across Western Washington will see rises but remain well below flood stage. Additional rainfall into next week could push the Skokomish River to at least action stage.

Outside of the river, rain rates Thursday night through Friday may be high enough to bring a risk of urban/small stream nuisance flooding, especially in areas with poor/blocked drainage (leaves will be falling during this event due to gusty winds). Risks to burn scars will also need to be monitored through this event. Felton/JBB

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 5 PM PDT this afternoon 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-Grays Harbor Bar- West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 6 AM to 6 PM PDT Thursday for Grays Harbor Bar.

Gale Watch from Thursday afternoon through Friday morning for Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-West Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Watch from Thursday evening through Friday morning for Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands.

Gale Watch from Thursday afternoon through late Thursday night for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.