textproduct: Seattle/Tacoma

SYNOPSIS

Upper level ridging over the Pacific Northwest will maintain warm and dry conditions across western Washington today. An upper level low approaching the region on Wednesday will bring the return of onshore flow, cooler temperatures, and chances of precipitation to the area. Upper level troughing will continue to influence the region heading into the weekend, keeping conditions cooler and cloudier across western Washington.

SHORT TERM /TODAY THROUGH THURSDAY/

Upper level ridging, with the ridge axis positioned over the Intermountain West, will continue to influence the area today, bringing clear skies and warming temperatures to western Washington. Winds remain easterly across the Cascades early this morning and primarily out of the north across much of Puget Sound, which has helped dry out the low levels, as well as advect some smoke into the area from regional wildfires. Today remains on track to be the warmest day of the week, with afternoon highs expected to climb into the mid to upper 80s across much of the interior and into the low 90s in the Cascade valleys. This will reintroduce Moderate HeatRisk to the valleys as well as the Everett-Seattle-Tacoma metro areas. Highs will remain cooler along the coast and generally in the mid 60s to low 70s. Winds will transition back to onshore later today, allowing for areas of smoke to push eastward tonight.

A pattern change is expected later tonight into Wednesday as an upper level low approaches the Pacific Northwest. This will bring the return of onshore flow, more widespread morning stratus, and cooler temperatures to western Washington. The low will push inland into British Columbia on Thursday, swinging the trough axis across western Washington. This will reintroduce chances of showers to the area, primarily along the Olympic Peninsula and for areas north of Everett, particularly over higher terrain. While overall QPF amounts look to remain light at this time, cannot rule out a few chances (between 10-15%) for thunderstorm development along the Olympics and North Cascades Thursday afternoon and evening. Afternoon highs will cool a few degrees each day across the interior and look to top out in the mid 70s to low 80s on Wednesday and low to mid 70s by Thursday. Highs along the coast will be in the mid 60s both days.

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

Ensembles remain in good agreement with upper level troughing remaining the dominant influence across the Pacific Northwest heading into the weekend, with guidance suggesting another trough moving southwards from British Columbia on Saturday. Onshore flow will continue and chances of showers will remain possible at times early in the weekend. A 10-20% chance of isolated thunderstorms will also be possible Saturday afternoon and evening. Uncertainty in the pattern increases by Sunday, though ensembles hint at drier conditions across the area as a transient ridge moves overhead ahead of a deepening trough offshore on Monday. Temperatures throughout the long term look to trend below normal, with afternoon highs expected to be in the mid 60s to mid 70s across the area. Overnight lows will be in the upper 40s to mid 50s.

14

AVIATION

Southwest flow aloft as upper level ridging continues to move eastward. VFR conditions at all area terminals early this morning. Marine stratus will slowly move along the coast this morning affecting primarily coastal terminals such as KHQM, bringing conditions down to IFR/LIFR. This stratus push is generally weaker than previous mornings, so expect coverage to be limited across the interior. Terminals such as KPAE and KPWT may see stratus and or brief fog development early this morning that could bring localized MVFR/IFR conditions. Otherwise, VFR will continue throughout the remainder of the day, with haze continuing aloft. NE winds 4 to 8 knots turning southerly this morning, maintaining the same speed.

KSEA...VFR this morning at the terminal. N/NE winds this morning around 8 to 12 knots, switching southerly 15z-17z and maintaining 5 to 10 knots the rest of the afternoon and evening. VFR conditions will likely continue the remainder of the TAF period, with low confidence of any stratus reaching the terminal this morning. Valley fog could develop near the terminal, keeping very low probabilities (10% or less) of LIFR.

Mazurkiewicz

MARINE

Surface high pressure will continue over the coastal waters today with a thermal trough along the coast this afternoon. Increasing onshore flow tonight and into Wednesday will result in small craft westerlies through the Strait of Juan De Fuca. Weak systems crossing over the coastal waters will continue the onshore flow pattern through the remainder of the week with continuous pushes each afternoon and evening down the Strait of Juan De Fuca.

Coastal seas generally remain around 4 to 6 feet throughout much of the week.

Mazurkiewicz

FIRE WEATHER

Warm and dry conditions are expected today, with upper level ridging over the region. Easterly flow across the mountains overnight will continue to promote additional drying near the Cascade gaps, where relative humidity values are expected to drop to near critical values in the low to mid 20s this afternoon. Elevated fire weather conditions are expected for the Cascades today as a result.

A pattern change late today into Wednesday will bring the return of moist onshore flow, excellent overnight relative humidity recoveries, cooler temperatures, and chances of precipitation to western Washington at times through much of the second half of the week. Overall, expect upper level troughing to help mitigate fire weather concerns for most areas. The exception will be in any isolated thunderstorm activity on Thursday and Saturday, particularly across the mountains. While the exact details on thunderstorm activity remain uncertain at this time, lightning from any storms that do develop may lead to new fire starts across the mountains and gusty, erratic outflow winds could impact ongoing fires within the vicinity of any storms.

14

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 5 PM this afternoon to 2 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.