SYNOPSIS
Very warm week ahead for Western Washington. Upper level ridge offshore today will slowly drift east over the weekend ending up over Western Washington Sunday and Monday. The center of the ridge will move off to the east Tuesday and Wednesday. High temperatures warming into the weekend peaking Sunday and Monday.
Gradual cool down beginning Tuesday with the ridge moving east.

SHORT TERM /TODAY THROUGH SATURDAY/
Little change in the forecast this morning. Heat advisory will remain in effect for the interior Friday afternoon through Monday evening and Friday afternoon through Sunday evening for the coast.

Satellite imagery shows clear skies over most of the area with a small patch of stratus and fog near Grays Harbor. Temperatures at 3 am/10z were in the 50s and lower 60s.

Upper level ridge over Western Washington today with the ridge axis offshore near 130W. Light flow in the lower levels turning northerly this afternoon. Stratus and fog near Grays Harbor will dissipate by mid morning. Clear skies over the remainder of the area. Temperatures aloft warming today with 850 mb temperatures rising from plus 10C to 14C to plus 16C to 18C by 00z Friday.
Northerly afternoon breeze will cut a couple of degrees off the high temperatures near the water. Highs mid 70s to mid 80s inland and lower to mid 70s coast.

Little change in the pattern tonight and Friday with the ridge axis remaining near 130W with northerly flow in the lower levels across the area. Ridge building a little resulting in slightly warmer temperatures aloft Friday afternoon, 850 mb temperatures in the plus 20c to 22C range. Lows tonight in the 50s. Highs Friday warmer with 80s and lower 90s inland and mid 70s to mid 80s coast.

Thermally induced surface trough along the Oregon coast Friday will try and move north Friday night into Saturday with the trough ending up over the Western Washington interior Saturday afternoon.
Even with the surface thermal trough low level winds above the ground to 850 mb remain northwesterly. Without a good switch to offshore flow highs Saturday similar to Friday, 80s and lower 90s inland and mid 70s to mid 80s coast. Lows Friday night in the mid 50s to lower 60s.

LONG TERM /SUNDAY THROUGH WEDNESDAY/
Extended models in good agreement with the upper level ridge drifting towards the coast Sunday. Ridge axis along the coast Monday moving inland Monday night and east of the Cascades Tuesday and Wednesday. Highs peaking along the coast Sunday, upper 70s to mid 80s, and over the interior Sunday and Monday, mid 80s to upper 90s. Weak onshore flow developing along the coast Monday as the ridge axis moves into the interior with the weak onshore flow spreading to the interior Tuesday as the ridge axis moves east of the Cascades.
Even with the ridge axis to the east temperatures aloft will only cool slightly Tuesday and Wednesday. With the onshore flow being rather shallow Tuesday high temperatures will only cool a couple of degrees in the interior, 80s to mid 90s. A little bit stronger onshore flow Wednesday lowering high temperatures a little more, upper 70s to near 90. Highs along the coast Monday and Tuesday in the upper 60s to mid 70s, Wednesday mid 60s to lower 70s. Lows Sunday night for the interior in the upper 50s to mid 60s and mid 50s to lower 60s Monday and Tuesday night. Lows along the coast in the mid to upper 50s.

Felton

AVIATION
High pressure and offshore flow will lead to a dry and stable air mass across western WA with VFR conditions.

KSEA...Clear with N winds, increasing to 10-15kt 21-03z.

33



MARINE
Strong high pressure remains offshore through the week, which will continue to dominate the weather pattern. A building thermal trough will bring breezy northerly winds to the coastal waters and Puget Sound. These will peak each afternoon and evening, and while mostly well below advisory criteria. There's some potential that winds over the outer coastal waters do occasionally get into the 20-25 kt range, but confidence is low. Meanwhile, the persistent northerly winds will maintain rather steep seas over the coastal waters with seas generally 5 to 7 feet at around 8 or 9 seconds for the remainder of the week.

12

FIRE WEATHER
Benign fire weather conditions are expected to remain through today. However, confidence is high on an amplifying upper-level ridge settling over the region beginning Friday. Not only will dry conditions persist, but hot weather is in the forecast thanks to easterly flow created by a developing thermal pressure trough along the coast. The heat is expected to peak over the weekend with the hottest temperatures likely on Sunday. Critical RH values are trending widespread over the Cascades with isolated areas within the Olympic Mountain valleys during this time. The hot and dry setting will be enough to maintain elevated fire weather conditions especially with fuels expected to dry out rapidly during this heat stretch. The next notable push of onshore flow will arrive Sunday night into Monday.
It'll bring decent RH recoveries to fire zones such as 650 but won't be strong enough to completely limit the threat for the Cascades early next week.

McMillian/18

SEW WATCHES/WARNINGS/ADVISORIES
WA...Heat Advisory from noon Friday to 10 PM PDT Monday for Admiralty Inlet Area-Bellevue and Vicinity-Bremerton and Vicinity- East Puget Sound Lowlands-Eastern Strait of Juan de Fuca- Everett and Vicinity-Hood Canal Area-Lower Chehalis Valley Area-Olympics-San Juan County-Seattle and Vicinity- Southwest Interior-Tacoma Area-West Slopes North Cascades and Passes-West Slopes North Central Cascades and Passes- West Slopes South Central Cascades and Passes-Western Skagit County-Western Whatcom County.

Heat Advisory from noon Friday to 10 PM PDT Sunday for Central Coast-North Coast-Western Strait of Juan De Fuca.

PZ...None.