textproduct: Seattle/Tacoma

SYNOPSIS

Upper-level ridge offshore will weaken tonight and Saturday as a system glances by to the north. The ridge will rebuild Sunday as its axis moves over western Washington Monday and Tuesday. This set up will kick-start a period of well-above average temperatures as HeatRisk becomes a concern. Conditions are favored to trend cooler towards the second half of the week.

SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/

An upper-level ridge will lose influence this evening as a low center traverses to the north over BC. As a result, low-level onshore flow is forecast to increase as an intrusion of marine cooled air takes hold of western Washington. Marine stratus will increase in coverage tonight as portions of western WA wakes up to mostly cloudy to overcast skies on Saturday. Overnight lows will fall to the upper 40s to mid 50s.

As mentioned - it'll be a cloudy start to the day for areas across W WA on Saturday. However, the marine layer will gradually burn off as the day progress giving way to mostly clear skies by the afternoon. Daytime highs are forecast to top out in the lower to mid 70s, around seasonal average. Saturday will likely be the coolest day for the next several days as conditions are expected to warm up rather significantly into early next week. Warmer conditions will kick into gear on Sunday as an upper-level ridge builds offshore and begins its gentle progression landward. High temperatures are expected to rebound back into the upper 70s to mid 80s. Overnight lows will generally fall into the 50s for both Saturday and Sunday.

LONG TERM /MONDAY THROUGH FRIDAY/

Ensembles are in lock-step in the positioning of an upper-level ridge overhead on Monday and it's axis east of the Cascades on Tuesday. A surface thermal trough looks to also develop and snake along the US west coast - leading to increased offshore flow. Daytime highs will warm into the upper 80s to upper 90s with the hottest day on Tuesday. There is a chance for record breaking highs and record high minimum temperatures Tuesday as well. Widespread moderate HeatRisk is favored along with a 20-30% chance of major HeatRisk across urban centers Monday through Tuesday.

A gradual cool-down is at play midweek onward. Conditions will still remain warm on Wednesday with highs in the 80s to near 90. However, near-seasonal conditions may return by Friday as guidance is hinting as the progression of an upper-level through the region.

AVIATION

VFR conditions with mid to high clouds this afternoon. Increased onshore flow evening/tonight will bring increased chances for widespread MVFR cigs. Highest chances (70-90%) are along the coast after 02z, with a slight chance (20%) of IFR cigs between 04z and 14z. For interior terminals, changes range between 25-50% between 11z and 16z. VFR conditions return tomorrow afternoon. Winds this afternoon 6-12 kts. Southwest (onshore) winds after after 06z-08z Saturday at 8-14kts.

KSEA...VFR conditions this afternoon with mid to high clouds. Onshore flow starting this evening will introduce the chances for MVFR cigs Saturday morning. Latest guidance has a 25-40% chance of MVFR cigs between 11z and 18z. VFR conditions return after. W/NW for the rest of the afternoon at 6-8 kt. Increasing SW winds after 06z- 08z at 6-12 kt.

MARINE

Broad high pressure over the offshore waters of the Pacific retreats to the west as a low pressure system moves through British Columbia this afternoon and Saturday, causing high pressure over Washington's waters to continue to weaken. Once the low pressure system pushes east, high pressure will quickly rebuild over area waters late Saturday evening and will strengthen through midweek.

Elevated winds and seas will continue for the coastal waters through Saturday and will begin to subside in the late afternoon to evening. Strong northerly flow will cause seas to build to 10-15 ft this evening through Saturday evening. As high pressure continues to strengthen over the waters early next week, increased northwesterly flow over the coastal waters will bring the chances of small craft winds Tuesday through Thursday, with the latest probabilities around 50-80%. Diurnal pushes through the Strait of Juan de Fuca will also begin today and will continue into next week. In addition, guidance is highlighting a 40-50% chances for gales in the Strait of Juan de Fuca on Tuesday through at least Thursday.

FIRE WEATHER

Elevated fire weather concerns on Monday and Tuesday with minimum relative humidity values dropping into the 20s in Cascade valleys. Can't rule out isolated teens as well. Fuels will continue to dry and the atmosphere may become conditionally unstable with the surface thermal trough Monday and Tuesday. Fuels are getting close to critical levels. Even without hitting critical levels needed for red flag warnings to be issued, fine fuels like grass and brush will ignite quickly with it being so dry. Lets continue to be careful out there.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 11 AM PDT Saturday for Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

Small Craft Advisory until 5 PM PDT Saturday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.