textproduct: Seattle/Tacoma

SYNOPSIS

Dry weather with a neutral flow pattern over Western Washington will continue today into Thursday. An upper level trough from the Gulf of Alaska will begin to sink down into the region Thursday into Friday, with an upper level low in California pivoting to the northeast, all over a surface trough across Eastern Washington. Showers will be likely Thursday evening into Friday morning for areas east of Interstate 5, along with a slight chance of thunder along the Cascade Crest. Warmer temperatures will linger through Thursday, before cooling down this weekend ahead of a warmup next week.

SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/

Western WA this afternoon sits under a small ridge/neutral pattern this afternoon (in between two upper level lows, one in the Gulf of Alaska, and one centered over the central California/Nevada border). Much of the area remains clear on satellite this afternoon, with a few areas of cumulus over the mountains, and a narrow cloud bank along the Pacific Coast. Temperatures this afternoon will continue to climb into the low to mid 70s, with lows tonight dropping into the low 50s. Winds will remain out of the north at around 5 to 15 mph.

The pattern shifts Thursday as the low/trough from the Gulf of Alaska begins to southward, along with the upper level low in California pivoting northeast. A surface trough/low also sits in eastern Washington that will remain in place ahead of a cold front being driven by the trough with the low in the Gulf of Alaska. While the first part of Thursday will be mostly clear, cloud coverage will build in later in the evening. Daytime temperatures will still likely reach the upper 70s/low 80s by the afternoon, with dew points in the mid to upper 50s in some spots (couple pockets of 60). The HeatRisk is minor going into Thursday, although it may feel slightly muggy with the combination of the warmer temperatures and dew points.

For precipitation Thursday night/Friday, convective ensembles have a complex of showers and thunderstorms forming in North- Central Oregon that will move to the north along the Cascade crest during the evening/early morning hours. By the time they reach Western Washington, it will be in the dark and more than likely the instability in the air will dissipate as the sun sets. There remains a 20% chance of thunder for locations along the Cascade Crest in the afternoon/evening for any convection that does make into the area ahead of sunset. Otherwise, the band of showers should be able to produce some beneficial rain for the region, with mean precipitation outputs showing around a quarter of an inch of QPF for areas east of I-5. The showers are expected to last into the first half of Friday.

In addition to the rain, winds may become breezy in a couple areas along the waters Friday morning as strong onshore flow pushes in behind the cold front, particularly the Pacific Coast and Strait of Juan de Fuca. These winds would peak early Friday morning, with potential for gusts up to 30-35 mph in these areas. Otherwise, the weather cools down significantly on Friday, with highs only reaching the upper 50s to low 60s. Cloud coverage likely remains in place during the day, with potential for the coast seeing some cloud breaks late.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

The models agree on the cooler/mild air hanging around the region through the weekend as the trough axis sits along the coastline. High temperatures Saturday and Sunday remain in the 60s, with lows in the 40s. Cloud coverage hangs on a bit going into Saturday, with most of it beginning to clear out by Sunday.

The trough moves completely out by Monday, inviting an upper level ridge to build over the region over a thermal trough building along the coastline. This will cause a significant warmup going into next week, with high temperatures returning into the 80s, and a chance for even a couple of 90s in the south interior on Tuesday. HeatRisk increases to moderate for Tuesday for areas in the interior away from water. Overnight temperatures Tuesday night into Wednesday morning may also struggle to drop below 60.

HPR

AVIATION

An upper level low will spin to our south tonight with another low spinning over the Gulf of AK. In between lies western WA under stable conditions. The flow aloft is N to E, becoming S Thursday morning. VFR conditions prevail across the region. The coast will see low clouds and IFR conditions early Thursday morning. Moisture will wrap N and E into western WA Thursday night (after 06z Friday) for showers. 33

KSEA...VFR conditions. N winds to 10 kt easing this evening. 33

MARINE

Small Craft Advisories remain in effect for the coastal waters for both wind and seas (through Friday). A strong onshore push will produce gales through the Strait of Juan de Fuca Thursday evening. Gales may persist through the day Friday and into Friday night. Wind and seas will ease and subside over the weekend. The flow will turn offshore early next week as a thermal trough forms along the coast. 33

HYDROLOGY

The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated during this time as needed.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Gale Watch from Thursday afternoon through Friday evening for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 5 PM PDT Thursday 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.