textproduct: Seattle/Tacoma

UPDATE

No major updates to the forecast today. Showers and thunderstormsare still forecast for late this afternoon through early Sunday as the system moves across the area. A few isolated strikes have been observed over the coastal waters this morning. See below for an update to the aviation discussion. 62

SYNOPSIS

Unsettled weather will move into western Washington this weekend with rain, showers, and the potential for thunderstorms. Drier conditions are expected to return by Monday, with temperatures gradually warming back up throughout the course of the week.

SHORT TERM /TODAY THROUGH MONDAY/

An upper-low is currently positioned over the offshore waters this morning. It'll track inland as the day progress bringing widespread rain, showers and a 15-25% chance of thunderstorms. The NBM has highest probability of lightning occuring over the Olympic Peninsula and southwest interior where HREF Surface Based CAPE has 250-500 j/kg present. Rainfall is forecast to arrive towards the late afternoon-evening hours on Saturday but can't rule out a few showers beforehand. The activity will persist overnight Saturday into Sunday morning before conditions trend drier by Sunday evening though, can't rule out lingering showers over the Cascades. 24 hour precipitation probabilities greater 2.00" range between 50-80% across the central and southern Cascades through Sunday night. Probabilities greater than 1.00" range anywhere from 30-60% across the Puget Sound lowlands into the southwest interior. Areas northward towards Bellingham won't be as wet. Winds this weekend should be generally benign but can't rule out local gusts upwards of 20-25 mph. High temperatures will remain in the upper 60s to around 70, with lows in the mid 50s.

Expect conditions to dry out area wide through the day on Monday with temperatures remaining the same as the previous days. The upper-low will be well east of the area, near the northern Great Plains by Monday evening. We'll be left in a regime of northwesterly flow aloft as a stout upper-ridge positions over the Gulf of Alaska.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Another trough will pass through early Tuesday, however moisture doesn't appear to be abundant with this feature. Wednesday is where the models have an upper level high building over the Pacific, with a split difference as to how long the high remains offshore going into late next week. Regardless, most will see a warm up along with continued dry weather. Highs in the lowlands will likely climb back into the mid/upper 70s (with perhaps a few 80s).

AVIATION

Upper level low near 45N/130W this morning will slowly move east into Oregon tonight then move into Eastern Washington Sunday. Southwesterly flow aloft this morning becoming southeasterly this afternoon and easterly overnight into Sunday morning. Onshore flow in the lower levels.

VFR ceilings today into tonight. MVFR ceilings developing from about KPAE south Sunday morning continuing through the day with rain. There is a 10% of thunderstorms across the region tonight.

KSEA...VFR ceilings today into tonight. MVFR ceilings developing around 09z Sunday continuing into Sunday afternoon. Variable wind 5 knots or less becoming southwest 6 to 10 knots around 00z. 33/Felton

MARINE

A broad 1010 mb low over the coastal waters today will weaken and move south into Oregon tonight. Weak low pressure remaining over the waters Sunday. High pressure will build over the coastal waters Monday and remain over the area through Wednesday.

Increasing onshore flow later today with small craft advisory westerlies in the Central and Eastern Strait of Juan de Fuca tonight. Seas remaining in the 3 to 5 foot range over the inner coastal waters and 4 to 6 foot range over the outer coastal waters into the middle of next week. Felton

FIRE WEATHER

Onshore moisture will increase this weekend as a trough moves across western Washington. The initial precipitation Saturday afternoon will be more showery (with a 15-25% chance of thunder, highest probs over the Olympics), but coverage will become more stratiform late Saturday night into Sunday, increasing the chances of a wetting rain for most (especially the south Cascades). As a result, the fire weather concerns will remain minimal going through the weekend and early next week. High pressure will build in south B.C. by midweek, with lower pressure offshore at the surface. The pattern will become drier with warmer temperatures, and additionally some models are showing brief breezy east to southeast winds Wednesday evening/Thursday morning. A few Cascade locations may see RH values dip into the 20s, though there remains some uncertainty in the ensembles at this time as to how strong and long the high pressure will remain late next week.

HPR/41

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 6 PM this evening to 6 AM PDT Sunday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.