textproduct: Seattle/Tacoma

SYNOPSIS

Upper level ridging will flatten into Thursday as troughing develops over the Pacific Northwest late this week. An upper low progresses across the region over the weekend bringing rain potential and cooler temperatures. Drier conditions are expected on Monday with a slow warming trend next week.

SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/

Mostly sunny conditions this afternoon with high clouds overhead. An upper ridge over the region will flatten tonight with troughing developing into Thursday. Onshore flow increases into Thursday resulting in cooler temperatures and increased clouds. Weak convergence Thursday evening into Thursday night may result in areas of drizzle or light rain across portions of the central Cascades. Troughing further deepens Friday as an upper low develops offshore of Vancouver Island. Drizzle may also exist Friday morning associated with widespread stratus, however, Friday is expected to remain predominantly dry with the upper low well offshore. Temperatures will peak this afternoon in the 70s to low 80s, with highs only reaching the mid 60s to low 70s by Friday.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

The upper low offshore will move inland over Washington and Oregon on Saturday. There remains some uncertainty in ensembles regarding the exact track of the upper low, leading to some spread in the QPF amounts, as well as the timing of rainfall. At this time, rainfall amounts are heaviest south of Snohomish County, particularly in the southern Cascades, with QPF amounts around 0.50" over Mt. Rainier area on the NBM. In addition, there is also a 15 to 25% probability of thunderstorms south of Snohomish County Saturday afternoon. The upper low continues to drift eastward on Sunday, with a slow drying trend during the day. The exception being the Cascades where lingering moisture is expected at least through Sunday AM. An upper ridge begins to build well offshore Monday for a slow warming trend. Predominantly dry conditions are then forecast into the middle of next week, but will need to monitor the existence of any weak troughing around the Tuesday timeframe as indicated by a small subset of ensembles. Either way, temperatures trend back to near normal early next week. JD

AVIATION

Flow aloft will remain primarily out of the west/northwest as a weak ridge moves east of the Rockies today, giving way to a trough tonight/Thursday. Terminals are VFR this afternoon, with high clouds expected to fill in going into the evening, with mid and lower clouds tonight/Thursday morning. The trough and increase of onshore will likely lead to widespread MVFR ceilings for most terminals Thursday morning, forming from 12Z and potentially sticking through 21Z before improving to VFR. The coast has a 30-40% chance of IFR conditions with the initial stratus onset, and a 20% chance of LIFR. Winds will remain northerly today at 5-10 kt, becoming 5 kt or less out of the west going into Thursday. The Strait of Juan de Fuca area will see higher gusts tonight/Thursday exceeding 20 kt.

KSEA...VFR through tonight, then a 40-50% chance of MVFR stratus from 12Z Thursday morning through as late as 21Z. North winds 5-10 kt today, becoming light out of the west Thursday at 5 kt.

HPR

MARINE

High pressure remains in the coastal waters through Thursday. An unsettled pattern will setup late Thursday through the weekend as a couple of frontal systems move through the waters. The first front will be mostly dry (except for a few showers), but will produce gusty north-northwest winds in the outer coastal waters over 20 kt Thursday, and also gusty west winds in the eastern Strait of Juan tonight/Thursday morning as onshore flow increases. The weekend system will produce more widespread precipitation over the waters (particularly on Saturday), with perhaps the far southern Puget Sound waters having a slight chance (15-20%) for thunder with the shower activity. Wind impacts are not anticipated at this time with this system. High pressure will rebuild over the waters next week, with conditions remaining benign.

Seas at 4-6 ft today will build on Thursday, reaching 8-11 ft in the outer coastal waters and 6-8 ft for the inner waters. Seas decrease to 4-6 ft Friday/Saturday, and 3-5 ft this weekend into next week.

HPR

FIRE WEATHER

A drying and warming trend peaks today leading to brief elevated fire weather concerns for the Cascades. However, this will be short lived, with onshore flow returning on Thursday as a weak and mostly dry frontal system crosses to the north. Cooler and more moist conditions will return over the weekend, with precipitation potential on Saturday into Sunday.

JD/15

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 11 PM this evening to 11 AM PDT Thursday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 5 AM Thursday to 5 AM 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.