textproduct: Seattle/Tacoma

SYNOPSIS

High pressure over the area will keep conditions generally dry but allow for colder overnight temperatures and likely morning fog development into early this week. A return to a more typically active pattern of lowland rain and mountain snow is expected late in the upcoming week.

SHORT TERM /TODAY THROUGH TUESDAY/

Latest radar imagery living up to what the building upper level ridge promises with no echoes present in the CWA. Current satellite shows the other thing that comes with upper level ridging this time of year as some fog is very present in some valleys, especially in the SW interior and the Chehalis river valley. Not to be left out, latest obs are showing some pretty chilly temps this early morning with most lowland locations reporting upper 20s to lower 30s.

Models remain consistent that this is going to be the way it is for the short term as the upper level ridge continues to build and the ridge axis slowly makes its way eastward. Outputs 24 hours ago suggested a flattening of the ridge around Tuesday but latest data suggests more of just a stop in the ridge building than any real flattening per se. That said, forecast is largely just a continuation of dry conditions, cold overnight lows in the lower 30s /mid 30s for water adjacent locations/ and the potential for overnight/morning fog. One minor thing to discuss is that the nBM wants to allow for a little bit of spill over from a system passing to the north over the ridge...bringing some Slight Chance to low-end Chance PoPs to the NW corner of the Olympic Peninsula. This feels a little overdone as ensembles completely flatline when it comes to PoP and QPF here in the short term...but ultimately, the chances are low enough where their inclusion does not alter current messaging.

High temperatures will hang out in the low to mid 40s during this period.

18

LONG TERM /WEDNESDAY THROUGH SATURDAY/

24 hours ago, there was a bit of a rift between deterministic solutions and ensemble outputs...deterministic models holding the breakdown of the ridge off until late week while ensembles kept things on track for the next frontal system coming in by Wednesday. At the time of this writing, solutions have pretty well aligned, as both sides of the fence agree on keeping precip out of the forecast until the new year. While some ensemble members continue to suggest precip working its way into the area as early as Wednesday afternoon, the general consensus /and ensemble mean/ is that this activity will hold off until Thursday afternoon. Once the precip moves in, however, it is back to the races...so to speak...as the first system looks to be an upper trough moving northward from CA, followed quickly by a deepening trough over the Pacific pushing through for much of the day Saturday. This far out, it is a little early to assess teleconnections and whatnot...but models are hinting at a potential atmospheric river for the Saturday system. At this time, this seems to be more pointed toward northern CA...but this will be something to monitor as next weekend gets closer and as solutions likely change.

As clouds start to move into the area for the second half of next week, overnight lows will get a bump upward, generally in the upper 30s to lower 40s while daytime highs see a more meager incremental increase...ranging in the upper 40s to around 50.

18

AVIATION

Generally VFR early this morning with areas of IFR/LIFR fog and low stratus generally south of the Puget Sound. Northwesterly flow aloft will persist through the TAF period as an upper level ridge over the northeastern Pacific builds into the area from the west. As skies continue to clear into the morning, fog will continue to expand across the south Sound and interior generating a range of MVFR to LIFR conditions for a few hours this morning. Conditions will scatter out by the late morning, with terminals returning to VFR by the afternoon. Surface winds will remain light around 3 to 8 kt, gradually shifting back to southerly this morning.

KSEA...VFR this morning with easterly winds slowly shifting southerly throughout the morning, with light speeds generally 6 kt or less. Low stratus is possible in the vicinity of the terminal between 12Z-18Z this morning, with a high chance (45% to 50%) of MVFR conditions developing at the terminal. Conditions are expected to improve to VFR by the late morning, with more of the same on tap later this evening.

15

MARINE

High pressure will continue to build across the coastal waters this morning and remain situated over the region into early next week. Seas will continue to subside towards 3-6 ft throughout the day today, though systems passing by to the north will allow for seas to build back towards 6-9 ft again by Monday.

Dense fog may develop over portions of the area waters with clearing conditions and light winds during the overnight periods the next few days and will likely restrict visibilities at times.

The next front then looks to drop down into the area waters by late Wednesday into Thursday, which will likely bring the next round of headlines to the area waters.

14/15

HYDROLOGY

No river flooding in the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.