Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
867 FXUS66 KSEW 210213 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 713 PM PDT Fri Sep 20 2024 .SYNOPSIS...Dry weather will continue Saturday as high pressure moves through the region. A chance of light rain will come via a disturbance on Sunday. The start of next weeks work week will start dry as temperatures increase back into the mid and upper 70s by Tuesday. A stronger cold front will pass through Wednesday into Thursday, with increasing chances of rain. && .SHORT TERM /TONIGHT THROUGH TUESDAY/...No major changes have been made this evening. The rest of the previous discussion can be found below with some timing changes. An updated aviation and marine section have been provided. Saturday will clear out to be the sunniest day of the weekend, with any cloud coverage overhead burning off quickly Saturday morning is drier air makes it way down towards the surface. This will also increase temperature back into the upper 60s to low 70s for highs (along with very light northwest winds). The pattern shifts back to unsettled Sunday. A small/weak shortwave trough is expected to pass over British Columbia Sunday. Part of the trough is able to dig down into Washington, but weakens as it becomes positively tilted due to a ridge building behind it. The precipitation chances remain for Sunday, but have dwindled in overall amounts. Lowland areas will most likely only see a few hundredths of an inch of rain. This does increase however going up towards Forks/Neah Bay, North Cascades, and Mt. Vernon up into Bellingham. Anywhere from a quarter to a third of an inch of rain is possible in these areas. Convection is not expected with this activity. Dry weather returns Monday as a ridge builds over the region, tilting northeastward. This will clear out most cloud coverage during the day, with temperatures still hovering in the upper 60s to low 70s. Winds will turn light northeasterly to easterly through the Cascades late Monday into Tuesday. .LONG TERM /WEDNESDAY THROUGH SATURDAY/...The ridge on Monday will continue to move inland on Tuesday, with flow aloft becoming more southwesterly on Tuesday. With the winds becoming more offshore on Tuesday, the temperatures will increase into the mid and upper 70s during the day. HeatRisk will only rise to minor in lowland areas (with potentially a couple isolated pockets of moderate in the interior). A trough is expected to follow the ridge, arriving by Wednesday into Thursday and Friday. This will bring a cold front through, decreasing temperatures into the upper 60s to low 70s. Rain chances will increase across the entire coverage area with this frontal passage. There appears to be at this time a better chance of wetting rain with this system, especially in the north Cascades and adjacent lowland areas. Some of the initial rain Wednesday may be heavier. This system is still several days out, and will be monitored for potential impacts due to possible heavier rain. HPR && .AVIATION...Northwest flow aloft continues tonight into much of Saturday before turning more zonal as a weak upper level ridge starts to flatten out. Light and variable surface winds at the time of this writing are expected to continue for most terminals overnight and into Saturday morning. Locations that do see a slight increase in wind speed...yet still less than 5 kts...will see the direction shift northerly. Remaining sites will join in that direction by Saturday afternoon. VFR conditions in place over much of W WA with an isolated case of MVFR conditions over central Pierce county. While most terminals may see some FEW to SCT low clouds...and thus remain VFR overnight...locations that typically tend toward lower cigs, such as OLM and PWT, will see MVFR to IFR conditions emerge by 12Z. Widespread VFR conditions expected to return by late Saturday morning. KSEA...VFR conditions with high clouds at times tonight into Saturday. Patchy fog and stratus may develop into localized areas of Puget Sound on Saturday morning, and while FEW to SCT low clouds are possible, lower cigs are not expected over the terminal. Light and variable winds early this evening before slowly transitioning to northerly tonight and for the remainder of the TAF period. 18 && .MARINE...Generally light flow expected into Saturday as a surface ridge expands over the Coastal Waters. The ridge will weaken on Sunday as a frontal system moves onshore into British Columbia. Ridging will build back into the area Monday into Tuesday for more northerly and weakly offshore flow early next week. Onshore flow then resumes the middle of next week with a frontal system moves towards the area. Winds will continue to subside along the outer Coastal Waters this evening. Otherwise, lighter winds expected over the weekend. Seas of 7 to 9 feet for the Coastal Waters will subside to 4 to 6 feet on Saturday, building to near 7 feet for the outer Coastal Waters on Sunday. JD/18 && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$