textproduct: Seattle/Tacoma

SYNOPSIS

Western Washington on the backside of an upper level ridge with low level onshore flow through the weekend. The ridge moves east Monday as a weak system moves by to the north. Upper level trough developing offshore Tuesday remaining through Friday. Dissipating system arriving Wednesday with another possible weak system Friday.

SHORT TERM /TODAY THROUGH MONDAY/

Satellite imagery shows stratus along the coast, over the western half of the Strait of Juan de Fuca and through the Lower Chehalis Valley. Mostly clear skies over the remainder of the area. Temperatures at 3 am/10z were in the mid 40s to mid 50s.

Not much going on weatherwise this weekend. Western Washington on the backside of an upper level ridge with westerly flow aloft over the area. In the lower levels light onshore flow. This morning the stratus is not making eastward very fast but with the longer nights, low level moisture and light onshore flow expect the stratus to form in place over the Puget Sound at or a little after sunrise. With the light flow in the lower levels areas of fog also forming around sunrise. The layer will be shallow and dissipate around midday leaving plenty of afternoon sunshine for the interior. Stratus will be tough to get rid of along the coast with just some late day sunshine. Highs mid 60s coast and mid 60s to lower 70s inland.

Little change in the pattern tonight and Sunday. Another round of late night and morning low clouds with patchy fog over the interior while the coast stays mostly cloudy. Sunshine in the afternoon over the interior will put highs in the mid 60s to mid 70s. Highs along the coast in the mid 60s. It will be a cool morning Sunday with lows in the mid 40s to lower 50s.

A few changes Monday but the forecast will remain the same. Upper level ridge moves off to the east while a weak system moves inland well north of the area. Weak low level onshore flow in the lower levels keeping the morning clouds afternoon sunshine scenario intact. Highs remaining in the mid 60s to mid 70s with lows in the mid 40s to lower 50s. Felton

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Models in good agreement through Thursday with an upper level trough offshore. Dissipating system moving into the area Wednesday for a slight chance of showers over the northern portion. GFS brings the trough into the area Friday while the ECMWF keeps the trough offshore. Ensembles have enough solutions with light precipitation to put slight chance pops in the forecast. Slow cooling trend with highs in the mid 60s to lower 70s Tuesday dropping to the lower to mid 60s by Friday. Lows remaining in the mid 40s to lower 50s. Felton

AVIATION

Westerly zonal flow will prevail aloft today. With very light to mostly calm winds this morning, MVFR marine stratus will struggle to progress inland on its own this morning past SHN/CLM. This will allow for additional development through the interior of western Washington to be very low-based stratus or fog for LIFR conditions. Low stratus and fog will continue to slowly fill in, with the greatest extent expected just after sunset, or around 14-17Z this morning. Clouds should slowly lift and scatter from around 17-21Z for most, through the coast may stay mostly cloudy through much of the day. VFR conditions will then prevail until late tonight/early Sunday morning with another round of low stratus and patchy fog expected.

Winds look to remain light for most though tonight, as well. A weak push through the Strait of Juan de Fuca this evening will switch wind directions through the Puget Sound from south to north.

KSEA...VFR conditions through most of the TAF period, with the exception of between around 13-17Z this morning as fog and low stratus is expected to develop around the terminal. Models show a relatively slow lift and scatter between around 17-20Z this morning before mostly clear skies then prevail until early Sunday morning. South/southwesterly winds 5 kt or less will transition to west/northwest this afternoon and remaining light northerly overnight into Sunday morning.

62

MARINE

Weak onshore flow will continue into next week as broad high pressure remains over the offshore waters. Weakening frontal systems moving by to the north through next week will help to increase onshore flow, allowing for increased chances for Small Craft Advisory conditions each evening with westerly pushes through the Strait of Juan de Fuca. Pushes will begin to increase tonight and Sunday evening, but will most likely remain below thresholds. Chances for meeting Small Craft thresholds rise to 50-80% by Monday evening, with slightly lower chances on Tuesday evening.

Seas remain 3 to 5 ft until Monday as incoming swell rises seas to around 6 to 8 ft. Seas remain in that range through mid-week.

62

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.