Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
783 FXUS66 KSEW 302143 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 243 PM PDT Tue Apr 30 2024 .SYNOPSIS...Shower activity will taper off overnight with unusually cool temperatures and areas of frost by Wednesday morning. Another weak system will slide to our south on late Wednesday into early Thursday. Drier and slightly warmer conditions are expected Thursday and Friday before more precipitation arrives late Friday and Saturday. && .SHORT TERM /TONIGHT THROUGH FRIDAY/...A low pressure system continues to progress east near Portland this afternoon. Isolated to scattered showers continue to wrap around this system and will gradually taper off through this evening. A stray thunderstorm or two still cannot be ruled out this afternoon, with the highest chances closer to Portland. Clearing skies and a cooler airmass will result in areas with temperatures reaching into the low to mid 30s tonight allowing for areas of frost development. A Frost Advisory remains in effect for tonight. A weak system will slide mainly south of the area late Wednesday into early Thursday bringing another window of possible shower activity, mainly south and west of Seattle. This will be followed by transient ridging Thursday into early Friday allowing temperatures to warm into the 60s Thursday and Friday. The next system will begin to spread precipitation across the area Friday afternoon and evening. .LONG TERM /SATURDAY THROUGH TUESDAY/...A broad upper level low will make its way to the coast Friday night. Cluster analysis continues to indicate disagreement in the evolution of this low. Roughly half of the members take the bulk of the low and associated precipitation to the south while the other half keep a more progressive pattern moving the system across Washington fairly quickly but with heavier rainfall. In either case, the system will be associated with at least some precipitation and wet conditions are likely late Friday through Saturday. Beyond the early weekend system, zonal flow and at least semi- active weather is expected to continue. This will keep temperatures in check and a chance of precipitation in the forecast. -Wolcott- && .AVIATION...Cool upper level trough shifting east tonight into Wednesday. Light flow aloft becoming northerly overnight. In the lower levels northerly flow this evening turning back to onshore overnight into Wednesday morning. VFR ceilings over most of the area with MVFR ceilings with scattered showers until 04z. Skies clearing from north to south after 04z with increasing middle level clouds after 15z Wednesday morning. Patchy visibility 1 sm or less Northwest and Southwest Interior 12z-16z. KSEA...MVFR ceilings lifting to VFR 21z-23z. Skies clearing after 05z. Light southerly winds switching to northerly 18z. Northerly winds 8 to 10 knots 22z-04z. Winds switching back to southwesterly 6 knots or less after 06z. Felton KSEA...Ceilings near 4000 feet this evening with skies clearing overnight. Increasing middle level clouds after 14z with ceilings aoa 6000 feet. Northwest wind 6 to 9 knots becoming southerly 6 knots or less after 06z. Felton && .MARINE...Low level flow becoming onshore tonight with surface high pressure building over the coastal waters. System moving southeast through the coastal waters Wednesday night moving into Northern Oregon early Thursday morning. Weak high pressure over the waters Thursday night into Friday. Next system splitting as it moves into the waters Friday night into Saturday. Another system arriving late in the weekend. Small craft advisory westerlies in the Central and Eastern Strait late tonight into early Wednesday morning. Seas near 10 feet tonight subsiding to 6 or 7 feet early Wednesday morning. Felton && .HYDROLOGY...No river flooding is expected over the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Frost Advisory from 8 PM this evening to 10 AM PDT Wednesday for East Puget Sound Lowlands-Everett and Vicinity-Hood Canal Area-Lower Chehalis Valley Area-Southwest Interior-Tacoma Area. PZ...Small Craft Advisory from 11 PM this evening to 5 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca. && $$