textproduct: Seattle/Tacoma

SYNOPSIS

Mostly dry and mild conditions will continue over the next week across western Washington as an upper level ridge remains over the region.

SHORT TERM /TODAY THROUGH MONDAY NIGHT/

Western Washington is wedged between a broad upper trough over the Northern Rockies and an upper ridge centered well offshore. The end result is northerly flow at the surface and aloft. The air mass is cool and quite dry with widespread dew points in the 20s. This will allow temperatures to fall to near freezing across south Puget Sound and the Southwest Interior overnight. Hence, there is a frost advisory in effect. The overall synoptic pattern doesn't change significantly on Sunday apart from a slight bump in heights and lighter north flow near the surface. We'll see another mostly sunny day and slightly warmer temperatures. A weak disturbance will produce some cloud cover and cooler temperatures Monday and Tuesday, but stronger upper ridging is still on track to rebuild midweek allowing a few spots south of Seattle to make a run at 70 degrees. No public updates expected tonight. 27

Northerly flow aloft will continue over western Washington through the weekend as an upper level ridge builds offshore. This will maintain mostly dry conditions across the region with a warming trend into Sunday. However, mostly clear skies tonight into Sunday morning may allow for continued cold low temperatures which may cause frost to develop along the Puget Sound southward. Otherwise, western Washington will see warming conditions under mostly sunny skies into Sunday.

Temperatures cool several degrees on Monday as a weak shortwave passes over the area, bringing increased onshore flow. This system will bring cloudy skies to much of the region, with chances for light showers over higher terrain.

LONG TERM /TUESDAY THROUGH FRIDAY/

Northwest flow will develop aloft on Tuesday as a high pressure ridge builds offshore. This will allow for another day of near- normal temperatures and cloudy skies, with chances for showers continuing over the mountains. The ridge axis will shift inland on Wednesday and Thursday, bringing warming and clearing to the region, with temperatures nearing 70 degrees east and south of the Puget Sound on Thursday.

By Friday, a cutoff low is forecast to develop along the west coast, but models show large differences over the placement of the low. This will influence conditions across western Washington, so for now the forecast for Friday and beyond remains uncertain.

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AVIATION

An upper ridge will remain offshore through the weekend, with troughing over the Intermountain West. This will result in continued northerly flow aloft. Light to weak onshore flow tonight into Sunday morning. Predominantly clear skies with VFR for the interior sites through Sunday. There remains approximately a 35 to 40% chance of LIFR/IFR cigs for KHQM generally between 12 to 18z on Sunday. Onshore flow will then increase Sunday night into Monday for a more widespread stratus push inland. North winds will weaken this evening, becoming light tonight into Sunday. W/NW winds increase Sunday afternoon.

KSEA...Clear conditions expected through the TAF period. North winds 5 to 10 kts this evening will decrease below 5 kts mainly after 06- 07z. NW winds increase again Sunday afternoon. JD

MARINE

High pressure will remain over the coastal waters, with lower pressure inland. North flow (offshore at times) will transition to more of an onshore pattern early next week. Models have a couple pushes down the Strait of Juan de Fuca Sunday evening and Monday evening, but the probability of gusts reaching small craft advisory thresholds is low at this time. The outer coastal waters may see breezy gusts up to 20 kt Monday/Tuesday, with a possible system end of the week producing breezy winds across more of the waters. Additionally, low clouds/fog Sunday morning along the Pacific Coast may reduce visibilities at times to mariners.

Seas this weekend hold around 4-6 ft, and increase to 6-8 ft Monday through next week.

HPR

HYDROLOGY

No river flooding is expected over the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Frost Advisory from 11 PM this evening to 10 AM PDT Sunday for City of Seattle-Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King Counties- Olympia and Southern Puget Sound-Southern Hood Canal.

PZ...None.