textproduct: Seattle/Tacoma

SYNOPSIS

Dry weather will largely continue for most in western Washington through the end of the week. A weak front moving through Thursday into Friday will have a slight chance of producing isolated showers in the south sound. A more organized upper low will dig south into the Pacific this weekend, chances of showers resuming Saturday through the middle of next week. Snow levels will drop to near 3,000 to 4,000 feet on Saturday, which may lead to some mountain snow showers, along with more widespread lows in the 30s on Saturday morning.

SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/

A split-flow pattern continues in the upper atmosphere with an upper level low deep into California, and the jet stream still north into Canada. Skies have cleared this afternoon with the only clouds high over the Pacific and north interior. High temperatures today will still warm into the mid and upper 60s (with a couple 70s down south). Cloud coverage increases tonight into Thursday with a weak cold front moving through in the morning. No precipitation is expected when the front passes through in the morning. However, there will be a 20 percent chance of showers with a post-frontal convergence zone in the afternoon for those in the south interior/south sound. Winds will likely increase out of the northwest on the Pacific Coast Thursday night, with gusts to 25 to 35 mph. Cloud coverage will clear Friday afternoon, although high temperatures will be a few degrees cooler (mid to upper 50s). Depending on how long the clear skies are able to hold on Friday night into Saturday morning, there may be instances of lows in the mid 30s for some frost potential (especially down in the south interior).

LONG TERM /SATURDAY THROUGH WEDNESDAY/

The models/ensembles are still having some trouble coming to an agreement as to how an upper level low/trough will develop and evolve going into this weekend into next week. Most operational runs have the low dropping south into the Pacific (just off the coast), though it becomes more split as to if the low will remain in place, or move out to allow for ridging to build in next week. This uncertainty will keep a chance of precipitation going into the weekend and into next week, with precipitation amounts not expected to produce any significant impacts. The coldest morning again will be on Saturday, with the best chance of frost development, and snow levels dropping briefly to 3,000 to 4,000 ft. Afterwards, temperatures and snow levels are favored to warm/rise slightly (especially if a ridge does indeed build over the region). The Pacific coast may also see another round of breezy winds Sunday, but will otherwise remain light.

HPR

AVIATION

An upper level trough will form offshore tonight then shift inland on Thursday. The flow aloft is W to SW. Skies remain VFR this afternoon and evening with increasing high clouds over western WA. The flow will turn onshore with the front moving in on Thursday. The cirrus clouds will be thin enough for patchy low clouds and fog in the interior again Thursday morning. Low clouds will burn off by 18-20z. Low level stratus clouds will increase Thursday night onshore flow. 33

KSEA...VFR tonight with increasing high clouds. Patchy low clouds in the interior once again Thursday morning with a burn off by 18-20z. N/NE winds to 5 kt becoming W/SW by 18z Thu to 10 kt. 33

MARINE

Weak high pressure will lead to generally light winds over the waters tonight. Wind and seas will increase on Thursday as a front moves inland. Highest wind and seas will be over the Coastal Waters - a Small Craft Advisory is in effect. Expect building seas to 10-15 ft Thursday night. Winds and seas will ease and subside on Friday. The flow will turn offshore this weekend as a deeper surface low spins south over the offshore waters. The low will weaken as it moves inland early next week. 33

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 2 PM Thursday to 11 AM PDT Friday 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.

Small Craft Advisory from 8 AM Thursday to 5 PM PDT Friday 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.