textproduct: Seattle/Tacoma

SYNOPSIS

A weak frontal system will clip the area today for increased cloud cover and cooler temperatures. Warming temperatures and high pressure return to the area early in the week, with Tuesday likely to be the warmest day. A transition to a cooler, more unsettled pattern is expected for the second half of the week.

SHORT TERM /TODAY THROUGH TUESDAY/

High and mid level clouds continue to stream across the area early this morning ahead of a dissipating frontal system that will shift onshore later today. We could get a pretty spectacular sunrise out of this in places. High temperatures will cool several degrees and a few spots near the coast and across the North Interior might get a shower or two. High pressure aloft will begin to rebuild into the region tonight into Monday with the low level flow turning northerly. After a few morning clouds, Monday will feature mostly sunny skies, modestly warmer temperatures and breezy north winds through Puget Sound. Thermally induced low pressure at the surface expands northward along the coast early Tuesday with the low level flow turning weakly offshore. This will give us a good spike in temperatures with most of the area, including the coast, seeing highs in the 70s and lower (even a few mid) 80s.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

The forecast picture, particularly on Wednesday, takes a more difficult turn as we transition to low level onshore flow and a closed upper trough approaches somewhere near the Northern California coast. The ensembles have been having a tough time for several days resolving how this will ultimately play out. It potentially puts Western Washington in a region of southerly flow aloft along with some diffluence and associated elevated instability. Throw in some daytime heating and we have a recipe for potential thunderstorms. It must be stressed that this scenario is highly certain at this time, but the potential is there. Forecast high temperatures across the interior on Wednesday are quite uncertain...i.e. Ensembles for Seattle have a 15+ degree spread for Seattle's high temperature.

Thursday into next weekend, the ensembles are settling into general agreement that upper troughing over the Northeast Pacific will send a series of weak systems across the area for a few days of cooler temperatures and periodic chances of some light precip. 27

AVIATION

Southwest flow aloft will increase ahead of a trough/front moving across the terminals late tonight. There is a low 30% chance of a shower across the Puget Sound this afternoon, although conditions are largely dry through the TAF period. Ceilings remain elevated for most areas, especially in the interior. The only concern for lower ceilings this morning is the return of stratus to the coast early this morning (conditions likely to be as low as LIFR on the immediate coastline through the morning). Elevated stratus further inland remains intact through the afternoon, keeping probabilities of lower ceilings low this morning, and most likely VFR throughout the day. A push behind the trough Monday morning appears likely, with stratus making it inland into the interior. Winds variable this morning out of the southwest/northwest this morning, solidifying to northwest by early afternoon with sustained winds 5-10 kt (couple gusts to 20-25 kt in the Strait of Juan de Fuca areas this afternoon).

KSEA...VFR expected today, with high clouds beginning to scatter later in the afternoon. Lamp has a 30-50% chance of MVFR stratus returning to the terminal Monday morning (from roughly 10Z-17Z). Winds variable between southwest/northwest this morning around 5 kt, becoming north/northwest today 5-10 kt. Couple gusts to 20 kt possible in the afternoon.

HPR

MARINE

A weak trough will move through the waters today, with a slight chance of a shower in the Puget Sound later in the afternoon. Behind the trough, an onshore push will likely bring gusty winds in the eastern two thirds of the Strait of Juan de Fuca this afternoon and evening. A small craft advisory was issued through tonight. Outside of this, winds remain relatively light and primarily out of the north through the week. A potential system midweek may bring another push through the strait. Additionally, while low stratus is expected off the coast next couple mornings, there is potential for some pockets of fog over the coastal waters (especially in areas where the wind is calmer).

Seas will hold around 4-6 ft through the week (with a brief jump to 6-8 ft midweek).

HPR

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...Small Craft Advisory from 11 AM this morning to 3 AM PDT Monday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.