textproduct: Seattle/Tacoma

SYNOPSIS

Upper level low moving out of the Gulf of Alaska moving down British Columbia coast to the Washington coastal waters Thursday. Strong for early September cold front associated with the low moving through late this afternoon and early this evening bringing rain and gusty winds. The upper level low will remain in the vicinity through the weekend for cool and unsettled weather. Possible drying trend Monday and Tuesday as the low moves out of the area.

SHORT TERM /TODAY THROUGH FRIDAY/

Satellite imagery shows upper level low just southwest of Haida Gwaii with the associated cold front off the coast near 128W. Rain started on the North Coast in the last hour. Slightly unstable air mass ahead of the front with doppler radar indicating some light showers over the foothills and Cascades. Temperatures at 3 am/10Z were in the mid 50s to lower 60s.

Everything still looks on track this morning. Upper level low will continue to drop south today. Cold front off the coast becoming slightly negatively tilted. This will slow down the eastward progress of the front. Rain spreading inland west of Puget Sound this morning and over the remainder of the area this afternoon. Slight chance of thunderstorms well ahead of the front this morning with the unstable air mass. South to southeast winds increasing along the coast and over the Northwest Interior and Admiralty Inlet later this morning. Windy conditions, 20 to 35 mph, continuing into the afternoon hours. Front reaching the coast late this afternoon. The wind advisories for the coastline, Northwest Interior and Admiralty Inlet remain in effect. Highs in the lower to mid 60s.

Front moving through the interior early this evening with steady rain changing to showers. Breezy conditions just ahead and with the front. Winds easing post frontal along the coast early evening and over the interior before midnight. Lows in the mid 40s to mid 50s.

Upper level low off the coast Thursday will slowly drift inland Friday over Oregon. Relatively cool and unstable air mass over the area keeping showers in the forecast with a slight chance of thunderstorms in the afternoons with a little daytime heating. Highs remaining in the 60s. Lows Thursday night in the mid 40s to lower 50s. The last time Seattle had a low in the 40s was June 8th ( 49 degrees ). Felton

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

Models in general agreement with the upper level low remaining in the vicinity through the weekend. This is not a scenario the models are going to handle very well as far as the exact placement of the low. At this point will have to keep at least a chance of showers in the forecast. Temperatures slowly warming with highs in the mid 60s to lower 70s. Lows in the upper 40s to mid 50s.

Model solutions in good agreement given the situation with the low kicking out to the east Monday and a weak upper level trough moving over the area Tuesday. This scenario would confine the shower chances to the Cascades both days. Highs remaining below normal, in the mid 60s to lower 70s. Lows in the lower to mid 50s. Felton

AVIATION

South to southwesterly flow aloft will remain in place over W WA as an upper level low continues to dig southward just west of the coastline. Surface winds at the time of this writing mainly southerly with speeds ranging 4-8 kts...give or take depending on location. Speeds are expected to ramp up from west to east as the front approaches...with western terminals seeing this increase by around 12Z and interior terminals closer to 14Z or 15Z...generally ranging 12-18 kts with gusts up to 30 kts possible. Speeds start to ease mid to late afternoon around 22Z to 24Z down to 10-15 kts with gusts up to 20-25 kts still possible. Speeds will remain elevated into tonight, generally ranging 8-12 kts, but gusts will no longer be a concern. CLM will be the exception, thanks to shadowing from the Olympics, with winds generally light and variable with speeds under 5 kts.

Cigs largely VFR, although MVFR conditions are present along the coast, over some of the islands and off and on at Sea-Tac. Increasing winds this morning should give cigs a boost...and even with incoming rainfall most terminals should remain VFR. Exceptions will be those that tend to favor lower cigs such as HQM, PWT and OLM, as MVFR conditions will be present from time to time, if not the duration of the TAF period. Rain will transition to showers by 00Z late this afternoon for most terminals, bringing a return to widespread VFR conditions this evening into tonight.

KSEA...MVFR conditions present at the time of this writing, but as winds increase around 12Z, should start to see conditions improve to low-end VFR. Strongest winds still look to start up late morning, although models put this occurring closer to 18Z than the 15Z currently in the TAF. Will likely nudge this forward for the 12Z issuance. Southerly winds at their peak likely to run closer to 10- 15 kts with gusts up to 30 kts possible. Speeds and gusts ease slightly mid-afternoon running more 8-12 kts with gusts up to 20 kts. Gusts drop off after 03Z, but speeds will remain within that 8- 12 kts range. Models still suggest a slight chance (15%) of thunderstorms in the afternoon, but with such low confidence, will not include in forecast for now.

18

MARINE

A low pressure system will continue its way across the region today as its cold front moves through W WA today while the low center moves down through the coastal waters on Thursday. Winds will be borderline for gales, however gusts remain likely (60-90%) to reach gale force across most of the coastal waters, and through the northern Salish Sea from Admiralty Inlet up through the East Entrance and into the Northern Inland Waters. Wind gusts through the Puget Sound and Hood Canal will increase this morning, reaching Small Craft Advisory criteria by afternoon and will continue into possibly the early evening hours. Portions of the central Strait of Juan de Fuca south and east of Victoria may also see Small Craft to gale force gusts, but the majority of the zone should stay sheltered from the strongest winds. The strongest winds area-wide should start to decrease following the frontal passage tonight. While winds will stay elevated over some of the interior waters, at this time it does not look like additional headlines will be needed. Broad low pressure will remain over region through the end of the week into this weekend though winds look to remain light.

Chances for isolated thunderstorms will pose a threat to the area waters today and Thursday, through probabilities remain minimal (10- 20% chc).

Seas 7-10 ft this morning increasing to 10-13 ft by noon. These heights will not linger, as seas return to 7-9 ft late this afternoon/early this evening and generally remaining there overnight with possibly a slight increase to 8-10 ft. Seas ease to around 4-6 ft by Thursday night and remain like so through the weekend.

18/62

FIRE WEATHER

Fire weather concerns remain low through the next week. A strong for the first week of September weather system will bring significant rainfall to the coast and Olympics through Thursday afternoon. Rainfall amounts in the Olympics in the 1.5 to as high as 3 inch range with 1 to 1.5 inches along the coast. Elsewhere amounts will be lower but most areas should see a wetting rain. Rainfall may pose a minor threat to highly sensitive and brand new burn scars. Chances for showers will continue through the weekend with a slight chance of thunderstorms Thursday and Friday afternoon. The risk of new fire starts is low due to the isolated coverage and the increased fuel moisture from the wetting rains. Even with a drier pattern next week temperatures will remain a little below normal keeping fire weather concerns in check. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory until 8 PM PDT this evening for Island County- Lowlands of Western Whatcom County-Port Townsend Area-San Juan County.

Wind Advisory until 5 PM PDT this afternoon for Grays Harbor County Coast-Northern Washington Coast.

PZ...Gale Warning until 11 PM PDT this evening for Admiralty Inlet- East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands.

Small Craft Advisory until 11 PM PDT this evening for Puget Sound and Hood Canal.

Gale Warning 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.