textproduct: Seattle/Tacoma

SYNOPSIS

Weak upper level ridge with light onshore flow in the lower levels through Thursday. Upper level low approaching from the southwest Friday will move into the coastal waters Saturday. Shower chances increasing Friday night into Saturday with thunderstorms possible. Low moves by to the north Saturday night. Upper level ridge rebuilding Sunday and Monday will move east Tuesday as an upper level trough develops off the coast.

SHORT TERM /TODAY THROUGH FRIDAY/

Satellite imagery shows low clouds along the coast have already moved through the Lower Chehalis Valley and down the Strait of Juan de Fuca to the Puget Sound at 3 am/10Z. Just some high clouds over the remainder of the area. Temperatures were in the 50s and lower 60s.

Stratus a little further east this morning versus the last couple of mornings and will move east of Puget Sound around sunrise. Like the other mornings the layer is shallow with top reports around 1000 feet msl. With the layer being so shallow locations in the lowlands from Snohomish county southward will see some patchy fog through mid morning. Layer retreating back to the coast late morning/midday with afternoon sunshine for the interior. Clouds hanging right along the coastline in the afternoon. Highs inland in the 70s and lower 80s, along the coast in the mid and upper 60s.

Not much change in the pattern overnight into Thursday. Low level onshore flow a touch weaker making it harder for the stratus to get east of Puget Sound for very long Thursday morning. Slightly shallower marine layer combined with slight warming aloft adding a couple of degrees to the highs. Lows in the 50s. Highs in the mid 70s to mid 80s inland and near 70 coast.

Pattern starts to change Thursday night into Friday. Upper level low well offshore approaching the area. Upper level flow becoming southerly sending middle and high level clouds into Western Washington. Increasing low level onshore flow Friday afternoon looks to be too late to make much of a difference in the temperatures. Lows again in the 50s. Highs Friday in the 70s and lower 80s interior and mid to upper 60s coast. Felton

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

Extended models in much better agreement in the 00z run. Upper level low continuing to approach Western Washington with the low over the coastal waters Friday night. System spinning out of the low moving through late Friday night into Saturday morning with scattered showers and a slight chance of thunderstorms. Low continuing to slowly move northeast Saturday night and Sunday with the shower chances confined to the northern portions Sunday. Upper level ridge rebuilding later Sunday into Monday. The ridge will shift east Tuesday with an upper level trough developing off the coast.

Highs Saturday much below normal, in the 60s and lower 70s. A little warmer Sunday but still below normal, lower 60s to mid 70s. Highs warming back to normal, in the 70s interior and mid to upper 60s coast Monday and Tuesday. Lows in the 50s through the period. Felton

AVIATION

Light southwesterly flow aloft with weak low level onshore flow through Thursday. LIFR ceilings with visibilities down to a mile or less above about 400 feet this morning. Ceilings over the interior lifting to IFR mid to late morning with just scattered clouds by 19-20z. Along the coast ceilings lifting to MVFR in the afternoon.

Stratus slowly moving back inland overnight getting just east of Puget Sound 12z-15z.

KSEA...Leading edge of the stratus deck 10-15 miles to the southwest at 10z. Stratus reaching the terminal 13z-14z with LIFR ceilings and visibility dropping to as low as a mile. Improving trend beginning around 17z with no visibility restrictions and IFR ceilings by 18z. Clouds dissipating by 19z. Southwest wind 4 to 8 knots becoming northwesterly around 02z. Felton

MARINE

Broad surface high pressure over the waters will weaken Friday. A weak surface low will move into the coastal waters Saturday then dissipate Saturday night. High pressure will rebuild over the waters Sunday.

Small craft advisory winds in the Central Strait Friday night otherwise winds remaining below 20 knots through the period.

Seas 3 to 5 feet for the most part through the weekend. Felton

FIRE WEATHER

Low level onshore flow creating good humidity recoveries overnight into the early morning hours will keep fire weather concerns at a minimum through Thursday.

System moving through the region Friday night into Saturday will elevate fire weather concerns. This system could produce thunderstorms mainly over the Olympics and Cascades. Any thunderstorms that develop may be capable of producing locally wetting rains alongside gusty and erratic outflow winds and abundant lightning.

Fire weather concerns decrease Sunday with the system to the north and high pressure building into the area. Low level onshore flow Sunday through Tuesday with morning stratus and afternoon sun, near normal temperatures, and generally calm winds. Felton

SEW WATCHES/WARNINGS/ADVISORIES

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