textproduct: Seattle/Tacoma

SYNOPSIS

Low level onshore flow today with weak system moving by well to the north tonight. Upper level ridge building offshore tonight will move east ending up over Western Washington beginning Saturday. Thermally induced surface trough developing along the coast Saturday night with the low level flow turning offshore. Record highs likely both Sunday and Monday. Upper level ridge weakening and low level flow turning onshore Tuesday for some cooling. Increasing onshore flow Wednesday bringing temperatures down to near normal.

SHORT TERM /TODAY THROUGH SATURDAY/

No major updates for the morning AFD issuance. -HPR

Satellite imagery shows patch of stratus over the northeast slopes of the Olympics otherwise clear skies over the area this morning. Temperatures at 3 am/10z were in the mid 40s to mid 50s.

Pretty normal mid June day across the area today with northwesterly flow aloft and light northwesterly surface gradients. A few places already reporting 100 percent humidity so could see patchy fog form this morning. What does form will be shallow and not last long. High temperatures with plenty of sunshine in the mid 60s coast and mid 60s to mid 70s inland.

Little change in the pattern tonight and Friday. Weak upper level system moving by well to the north tonight will keep the light northwesterly low level onshore flow pattern intact. Weak system will also delay the ridge building over the area into Friday afternoon. Lows tonight in the 40s and lower 50s. Highs Friday just a touch warmer with the ridge starting to build, in the mid 60s to upper 70s.

Upper level ridge offshore building Friday night and Saturday with the ridge axis Saturday on a line from off the coast through Vancouver Island into the interior of British Columbia. Northwesterly onshore surface gradients continuing giving locations near the water a good seabreeze Saturday afternoon. This will knock a few degrees off the highs in locations near the water. Away from the water temperatures aloft warming with the ridge building will start the warming trend. Highs in the mid 70s to mid 80s.

LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/

Good run to run consistency in the models. Thermally induced surface trough developing along the coast Saturday night turning the low level flow offshore. The offshore flow will continue into Monday. Temperatures aloft warming with 850 mb temperatures peaking near plus 20C Monday. Record high temperatures both days with highs in the 80s and lower 90s Sunday and 80s to mid 90s Monday. Moderate HeatRisk both days with a 30-50% chance of Major HeatRisk in the Southwest Interior and Lower Chehalis Valley. Lows will be mild, in the mid 50s to lower 60s.

Forecast high for Seattle Monday is 91 degrees. 90 degree plus days are not unheard of this time of year but are rare. Only 7 percent ( 19 out of 276 ) of the 90 degree plus days at Seattle-Tacoma airport have occurred in May and the first half of June. Last year Seattle also had an early first 90 degree plus day with 90 degrees on June 8th.

Upper level ridge weakening Tuesday with the low level flow turning onshore during the day. Models yesterday were trending towards a weaker marine push scenario and the current runs have gone that way with 5-10 degrees of cooling for the interior. Much cooler on the coast with highs in the 60s. Lows Tuesday morning will be the warmest of the extended period, a few degrees either side of 60.

Ridge continuing to weaken Tuesday night into Wednesday with increasing low level onshore flow. Marine layer moving into the interior Tuesday night into Wednesday cooling highs back down into the lower to mid 70s. Highs on the coast mid 60s. With the arrival of the refreshing marine air lows Wednesday morning in the lower to mid 50s. Felton

AVIATION

VFR with clear skies expected today. Remaining patchy fog in the south interior has cleared. Increasing northerly winds 5-12 kt this afternoon, with the strongest winds along the coast and Strait of Juan de Fuca. Tomorrow morning, the probability of low ceilings and or/visibilities is 40-60% along the coast, 60-80% in the mountains, and less than 10% in the interior/Puget Sound areas. The ceilings/visibilities along the coast/mountains may be as low as IFR/LIFR at times Friday morning, before clearing.

KSEA...VFR conditions expected. Northeasterly winds early this morning 4-6 kt will transition to the northwest after 16z at 5-8 kt. Winds will revert back to the northeast after 06z.

29/HPR

MARINE

Another push of westerlies is expected this evening across the Strait of Juan de Fuca. With, moderate to high confidence, a Small Craft Advisory has been issued for the central and eastern portions of the Strait. Broad high pressure will continue to build over the NE Pacific today. On Friday, high pressure will begin building over area waters and will remain the dominant weather feature through Monday. With high pressure situated over area waters, northerly flow will be established across area waters. High pressure will weaken on Tuesday as the broad area of high pressure retreats back into the open waters of the Pacific. Long term guidance highlights increased onshore flow on Tuesday with the potential (50-70% chance) for gales across the Strait of Juan de Fuca.

29

FIRE WEATHER

Warm, dry and unstable pattern developing over Western Washington Saturday with the pattern continuing through Monday. Wetting rains earlier in the week will briefly help the fine fuels from reaching critical thresholds this weekend into Monday for red flag conditions. Minimum relative humidity (RH) values will drop as low as 15 to 20 percent for portions of the South Puget Sound and Southwest interior Sunday and Monday. These dry humidity values, combined with an unstable airmass due to daytime heating and light offshore winds will lead to elevated fire weather concerns across the region. Fuels that will be most susceptible to the elevated fire weather concerns are dry/shrubby grassy areas (especially those near roads), as well as piles of dry fuels. Low level onshore flow will return Tuesday, with a gradual cool down and improvement in minimum relative humidity values. Felton/HPR

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 2 PM this afternoon to 1 AM PDT Friday for Central U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 5 PM this afternoon to 1 AM PDT Friday for East Entrance U.S. Waters Strait Of Juan De Fuca.