textproduct: Seattle/Tacoma

SYNOPSIS

Onshore flow will continue bringing continued cooler temperatures this weekend. A warm and dry pattern moves in Monday through Wednesday, with temperatures peaking on Tuesday as an area of moderate HeatRisk builds over much of Western Washington. Late next week likely features a return of cooler conditions with occasional showers as the next upper trough arrives.

SHORT TERM /TODAY THROUGH MONDAY/

Clouds over a weak convergence zone over the central and southern Puget Sound lowlands will lift and scatter early this morning, giving way to mostly clear skies by this afternoon. With upper level troughing moving through the area, onshore flow will remain relatively elevated, keeping temperatures seasonably cool for this time of year. High temperatures will reach the low to mid 60s. Low temperatures tonight will also be a touch cooler, in the low to mid 40s. Some outlying areas may briefly dip into the upper 30s. Mostly clear skies will continue to prevail across the area on Sunday with western Washington on the west side of a trough/east of a building ridge. High temperatures a bit warmer, into the mid to upper 60s.

Monday will be the the start of a brief but rather abrupt warming pattern as the ridge continues to build just offshore, allowing for a weak thermal trough to get started along the coast. This will start to bring weak offshore flow into the equation through the overnight hours. High temperatures on Monday jump into the mid to upper 70s. Low temperatures Monday night jump into the low 50s.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Ensembles remain in good agreement with a building ridge over the region Tuesday and into Wednesday. This high pressure aloft will bring a light offshore flow pattern as the air mass warms, bringing temperatures into the 80s for the lowlands on Tuesday as the thermal trough builds into the Puget Sound region. The warmest locations in the South Sound could even make a run at 90 degrees. This will bring HeatRisk up into the Moderate (Orange) category for much of the area away from the water from Snohomish County all the way south through Lewis County. Areas closest to the waters of Puget Sound will remain somewhat cooler. While the offshore flow doesn't look terribly strong at this point, it will help to bring drier conditions with daytime humidity values down toward 25% - see the fire weather section for more details on this hazard. With the warmer conditions, it's worth noting that many area waters, especially those flowing from the mountains, remain quite cold.

Temperatures then moderate a bit later in the week, with Minor HeatRisk lingering as the ridge flattens and onshore flow resumes across the region. While some rain showers will be possible at times as this next disturbance approaches and moves into the region, it doesn't appear to bring much in the way of meaningful rainfall amounts.

AVIATION

Southwest flow continues aloft with upper level troughing over the northwestern U.S. Much of the area is VFR with scattered low to mid level clouds, as well as remnants of a convergence zone over the central/southern Puget Sound area. Clouds may continue to fill in throughout the morning, but guidance is maintaining that ceilings will remain VFR, with relatively low (15-20% or less) probabilities of MVFR ceilings this morning. Therefore, will trend with VFR prevailing. Clouds look to break up through the morning, allowing VFR conditions to prevail through the TAF period. Most locations are seeing light and variable winds this morning, with the exception of through and near the Strait where west winds 10-15G20 kt continues. Winds during the day will primarily be NW 5-10 kt, with gusts up to 20-25 kt at HQM and CLM where the strongest winds will be.

KSEA...VFR conditions through the TAF period. CIGs around 030-040 kft will remain through 18Z this morning, but guidance remains confident on remaining VFR (10% prob. of MVFR). E/SE winds around 5 kt will continue to veer towards NE after 18Z this morning, up to 5- 10 kt through the day.

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MARINE

Elevated onshore flow will continue through today across the area waters as low pressure over the intermountain west gets pushed eastward. Small Craft Advisory winds will continue to persist through much of the day today. There will likely be a brief lull through the latter half of the morning before winds begin to rise once again this afternoon into tonight. Winds look to ease late tonight into early Sunday morning as high pressure builds back over the coastal waters. However, as that builds, northwesterly winds will also begin to rise over the coastal waters, peaking Sunday night and nearing SCA criteria, and easing into Monday. This will also allow for waves to steepen and rise to around 7-9 ft during this period before easing with the winds on Monday. High pressure weekends and the gradients weaken on Monday and Tuesday for calmer conditions to start the week. A frontal system looks to approach and traverse the area waters mid-week, which at this time, looks to increase onshore flow and may warrant additional headlines through the Strait of Juan de Fuca as winds increase. Excluding the aforementioned period Sunday into early Monday, seas look to remain 8 ft or less through the forecast period.

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FIRE WEATHER

An upper level ridge will setup a drier pattern on Monday and Tuesday, with maximum temperatures reaching into the 80s (with a few local spots touching 90). Expect a weak thermal low to build north over the region, with some light offshore flow developing. At this point, winds don't appear too strong, but a few locations near the Cascade gaps could see gusts to 20 mph. This will help to bring drier conditions in to the area with daytime RHs down approaching critical thresholds. This stretch appears short- lived, with a resumption of onshore flow bringing higher humidities for the second half of the week.

HYDROLOGY

The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated during this time as needed.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until midnight PDT tonight for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.