000 FXUS66 KSEW 011123 CCA AFDSEW Area Forecast Discussion...CORRECTED National Weather Service Seattle WA 423 AM PDT Thu Oct 1 2020 .SYNOPSIS...Upper level ridge over the area through Friday will shift east Saturday. Dry upper level trough moving through Sunday with another upper level ridge building next week. && .SHORT TERM /TODAY THROUGH SATURDAY/...Satellite imagery shows upper level ridge over Western Washington with a weak system riding over the top of the ridge in British Columbia. Low clouds along the coast with patchy fog inland. Temperatures at 3 am were mostly in the 50s. Upper level ridge remaining over the area today with the ridge axis along the coast. Light surface gradients continuing which combined with the smoke aloft will make it hard for the stratus along the coast to dissipate. Fog already forming in a few places with Shelton and Friday Harbor reporting a quarter of a mile at 3 am. A little more fog forming before sunrise but the fog will be shallow and dissipate by mid morning. For the remainder of the area smoke aloft will be hanging around today maintaining hazy skies. Highs mostly in the lower to mid 70s over the interior with mid 60s along the coast. Upper level ridge amplifies a little tonight changing the flow aloft to southerly over Western Washington. This could pull in some more smoke aloft in the evening hours into Western Washington. Little change in the lower levels with light flow continuing into Friday morning. Stratus along the coast will continue with patchy fog developing late over the interior. Lows tonight in the upper 40s and 50s. Upper level ridge axis shifting inland on Friday. Increasing onshore flow in the afternoon developing too late to bring any of the coastal stratus inland and cool daytime high temperatures significantly. Upper level ridge centered over California with light flow aloft there should help shut off the flow of upper level smoke over Western Washington. Highs in the lower to mid 70s inland with lower to mid 60s along the coast. Upper level ridge shifting east of the Cascades Friday night into Saturday with low level onshore flow increasing Friday night. This will push the coastal stratus deck inland Saturday morning. The onshore flow will be weak keeping the marine layer shallow enough to allow for afternoon sunshine over the interior. Lows Saturday morning in the 50s. Highs Saturday a little cooler over the interior with mid 60s to lower 70s. Highs along the coast remaining in the lower to mid 60s. .LONG TERM /SUNDAY THROUGH WEDNESDAY/...Extended models in good agreement with a dry upper level trough moving through the area early Sunday. This will enhance the marine layer over Western Washington Sunday morning. The deeper marine layer will mean more morning clouds over the interior and a later break out into the sunshine in the afternoon. Sunday will be the coolest day in the next week with highs mostly in the 60s. Another upper level ridge building behind the trough Sunday night into Monday with 500 mb heights climbing back up into the mid 580 dms. Low level flow trying to turn offshore Monday. Upper level ridge with light offshore flow Tuesday. Models continue to show good consistency with the ridge beginning to break down Wednesday. Another round of above normal high temperatures Monday and Tuesday with mid 60s to mid 70s for the interior and 60s along the coast. Slightly cooler Wednesday with the ridge weakening. Felton && .AVIATION...A return to onshore flow has led to the advection of a shallow marine stratus layer this morning, while a weak disturbance higher in the atmosphere is carrying some mid level clouds across the northern half of W WA. The marine stratus layer will continue to advect eastward through daybreak, encompassing most lowland locations and dragging ceilings down into the LIFR-IFR categories at all TAF sites. Fog will also accompany portions of the stratus, which will lead to vsby reductions down around LIFR or below. Will then see gradual improvement towards the afternoon, with clear skies south (some high level smoke still possible) and scattered mid level clouds north. Thursday night/Friday morning will be a repeat of stratus advection into the interior lowlands through daybreak. Winds will be light thru the period, calm through much of the morning with a light northerly component this afternoon around 5 kts (more westerly at HQM and CLM). KSEA...VFR conditions giving way to LIFR-IFR ceilings around 12z. Some fog will develop in the vicinity but confidence too low to mention in current TAF. Skies clearing this afternoon. Winds calm overnight, becoming N around 5 kts this afternoon. && .MARINE...Latest surface analysis this morning shows high pressure over most of the local area. This has allowed for generally calm winds and the return to light onshore flow. IR satellite imagery shows marine stratus encompassing the offshore waters and building eastward into the interior. Expect all waters to be mostly cloudy to overcast by daybreak this morning, with some fog accompanying the low clouds. Conditions will gradually improve through the day with stratus retreating back to the coast and continuing across portions of the Strait. As skies clear this afternoon, some smoke aloft is possible but will not pose any marine related impacts. Tonight/Friday morning will essentially be a repeat of this morning with marine stratus redeveloping and pushing inland. Onshore flow will prevail through the weekend and into much of next week, with varying amounts of morning cloud with clearing during the afternoon. Evening pushes down the Strait of Juan de Fuca can be expected, with small craft advisory level winds likely Saturday night into Sunday. The next frontal system looks to hold off until the latter portion of next week. Seas remain tranquil through much of next week, generally between 5 and 7 feet over the offshore waters. Kovacik && .HYDROLOGY...No flooding is expected on area rivers through the next 7 days. && .CLIMATE...Record high for Seattle today 89 degrees set in 1987. This is by far the warmest October day on record in Seattle with the second warmest day 83 degrees on October 11, 1991. 80 degree plus days in Seattle in October are rare with only 7 since records started in 1945 at Sea-Tac. The last 80 degree plus day in October in Seattle was October 3, 1993 ( 80 degrees ). Felton && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$ www.weather.gov/seattle
NWS SEW Office Area Forecast Discussion
Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather
