Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
667 FXUS66 KSEW 222145 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 245 PM PDT Sat Jun 22 2024 .SYNOPSIS...An approaching trough and cold frontal system will bring a few showers across the region late this afternoon into Sunday, primarily in northwestern Washington. The onshore flow will also lead to cloudier and cooler conditions for Sunday. Once the system departs, mix of clouds and sun will hang around until another weak disturbance passes through for Thursday with the chance of showers. Temperatures will remain relatively cool and slightly below average for the first full week of summer in Western Washington. && .SHORT TERM /TONIGHT THROUGH TUESDAY/...Satellite this afternoon shows quite a bit of cloud cover continuing to roll in ahead of an upper level low/trough, and surface cold front this afternoon. With the sky coverage quite thick, the mostly clear skies this afternoon were taken out, filled in with 60-70 percent sky coverage for the afternoon. There still may be a few peaks of sun and blue sky here and there, but with the system approaching from the west, the ceilings will gradually begin to lower going into late tonight and Sunday. Temperatures for Saturday afternoon have struggled to climb due to the cloud cover. Highs were lowered into the low to mid 70s for all interior areas. The warmest spots today will be in the southwest interior (where clearing of the cloud coverage was greatest). Additionally, relative humidity (RH) values have not dropped as much with the cloud coverage (ranging from around 30 to 55 percent). Few gusty southwest winds to 20 mph are possible this afternoon ahead of the front, but otherwise, fire concerns have decreased with the increase of cloud coverage. The cold front/upper level low comes through western Washington late tonight into Sunday. A few sprinkles have formed ahead of this front (which is still off the Washington coast), but more showers will increase along the coast and north of Everett late tonight into Sunday. These will dissipate by late Sunday afternoon/evening (but may linger around the Snohomish County area if a post-frontal convergence zone develops). Amounts will remain light (few hundredths to over a tenth of an inch of QPF). Behind the front, winds will become light out of the west, and high temperatures will struggle to get out of the 50s (few low 60s in urban areas). Monday and Tuesday will see an upper level ridge move over the region, which will dry out the region. With onshore flow remaining through most of the period, will likely still see some clouds in the morning Monday/Tuesday (particularly on the coast), with partial clearing taking place later in the afternoon. Temperatures will return into the 70s by Tuesday, with winds remaining light. Heat risk concerns remain none or yellow (in urban areas). .LONG TERM /WEDNESDAY THROUGH SATURDAY/...The upper level ridge is expected to slide eastward Wednesday into Thursday, with a trough coming in behind it for Thursday. As a result, expect Wednesday to have more cloud coverage, continuing into Thursday. Showers will be possible with the disturbance passing through Thursday into part of Friday. At this time, the threat for thunder is low and precipitation amounts are expected to remain light. Ensembles appear to favor keeping western Washington in the clear behind this system next Saturday into next week. Temperatures will still remain in the 70s (with Thursday being the coolest day with highs predominately in the 60s). Winds will remain light at 5 to 10 mph. HPR && .AVIATION... Southwesterly flow aloft will persist across western Washington into Sunday as an upper level ridge shifts further to the east and an upper level trough approaches the region offshore. Flow aloft will increase tonight into Sunday. In the lower levels, light onshore flow will gradually increase tonight. Mid to high level clouds continue to stream overhead the region this afternoon as a weak frontal system moves across the coastal waters. Conditions are VFR across the area terminals this afternoon. Expect ceilings to lower towards IFR, 500-1000 feet, along the coast tonight most likely between 00-03Z. Conditions along the coast could even dip to LIFR at times. Across the interior, expect ceilings to lower down to 5000 feet likely between 00Z-03Z and to MVFR, 2000-3000 feet, between 06Z-09Z. MVFR ceilings look to continue into Sunday and look to lift towards VFR, 3500-5000 feet, again by the late morning. KSEA...VFR with mid to high level clouds streaming overhead this afternoon. Ceilings will lower down to around 5000 feet around 03Z and to around 2000 feet between 06Z-09Z Sunday. MVFR ceilings look to continue through Sunday morning, before lifting back to VFR by late morning. Southwesterly wind persisting at 8-12 kt into Sunday, with a few gusts to 18-20 kt possible at times. 14 && .MARINE...A weak front will continue to make its way across the waters today. Onshore flow will increase behind the front tonight. Weak high pressure will then build into the coastal waters in its wake and interact with lower pressure inland Sunday through Tuesday. Another system will move across the area waters Wednesday into Thursday. With onshore flow increasing, expect small craft westerly winds in the Central and Eastern Strait of Juan de Fuca to increase tonight and to continue into Sunday morning. Seas continue to hover around 3 feet today and will build toward 6-8 feet Sunday as a larger westerly wave group arrives. Seas will then subside back towards 5-7 feet Monday and 2-4 feet near midweek. 14 && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 5 AM PDT Sunday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. && $$