Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
126 FXUS66 KSEW 240331 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 831 PM PDT Sun Jun 23 2024 .UPDATE...Clouds continue this evening across an area of weak convergence over northern King, Snohomish, and Skagit counties, as well as over the mountains. Lingering moisture may bring light rain at times in the convergence zone area tonight, with minimal QPF amounts. Otherwise, patchy fog may be possible in areas of clearing in Monday morning. No major updates this evening. && .SYNOPSIS...Troughing will slowly slide out of the area on Monday with ridging building into the Pacific Northwest. Onshore flow will keep a few clouds along the coast, with most areas maintaining dry conditions and warming temperatures through Tuesday. Another weak disturbance will pass through Wednesday and Thursday, returning the chance of showers, and near normal temperatures for all of western Washington. && .SHORT TERM /TONIGHT THROUGH THURSDAY/...Upper level 300 mb analysis shows an upper level low positioned over west central B.C. Canada, with a trough digging down into Washington and Oregon. Dynamically speaking (in terms of vorticity and jet streak energy), there has been enough support for cloud coverage and a few showers across the region this morning and afternoon. With last night`s weak cold front (now a surface trough) east of the Cascades, there will be a potential for convergence zone showers across Snohomish/King County border area this afternoon and evening. These are expected to remain light. Highs today remain quite a bit below average (by 5 to 10 degrees for some areas), with temperatures not expected to climb much past 60. Overnight, the trough will fill in over the region, becoming more of a zonal onshore flow pattern for the first part of Monday. There will likely be a mix of low stratus clouds, or potentially patchy fog in some areas, especially along the coast (depending on how much clearing there is Monday morning). Otherwise, models pick up on high pressure building via an upper level ridge, that will pass inland late Monday into Tuesday. The high temperatures will still be close to average for Monday (upper 60s to low 70s), but with models hinting at skies being a lot clearer for Tuesday, many areas will see highs soaring from the mid 70s to the low 80s for urban areas. Heat risk remains yellow (minor) with a couple tiny pockets potentially reaching orange (moderate). With winds remaining relatively light, this may make it harder to cool off (if working outdoors). The pattern will return to unsettled by Wednesday as an upper level trough will swing into western Washington. This is expected to be accompanied by an occluded/cold front down at the surface. Shower chances will increase during the day Wednesday. Depending on how cool aloft the air gets, will have to watch for a few isolated thunderstorms (at this point the risk remains in the northeast Cascades). A few gusty winds 15 to 20 mph are possible Wednesday afternoon. Temperatures will drop into the mid and upper 60s on Wednesday. .LONG TERM /FRIDAY THROUGH MONDAY/...Shower chances continue into Thursday from the system on Wednesday. With models showing the system moving through a little bit quicker, the showers may be wrapped up by Thursday afternoon. There is a little bit of uncertainty from Friday through Sunday on how much ridging will take place behind the trough. Looking ahead, it appears Friday will be the driest day in this period, with another trough bringing a chance of showers Saturday night through Sunday. Onshore flow will keep temperatures seasonal. HPR && .AVIATION...Upper level trough over Western Washington will move east tonight. Zonal flow aloft tonight and Monday. Onshore flow will persist in the lower levels through Monday. Satellite imagery shows a good portion of western Washington under cloud cover this evening. VFR ceilings for most terminals. High-res guidance continues to indicate weak convergence zone showers persisting over northern King and Snohomish counties this evening into Monday, which could bring localized MVFR to IFR ceilings to KPAE at times. Ceilings look to lower towards more widespread MVFR overnight into early Monday, however look to scatter and lift for VFR conditions near 18Z Monday. KSEA...VFR ceilings through tonight. NBM guidance has a 35 percent chance of MVFR ceilings developing at the terminal between 12-15Z Monday. High-res guidance indicating CZ showers will likely stay to the north of the terminal. Southwest wind persisting at 10-14 kt, with gusts to 20-25 kt possible at times into this evening. Winds will ease back to 4-8 kt after 03Z and look to transition to the north and increase to 5-10 kt between 18-21Z Monday. 14/McMillian && .MARINE...Weak high pressure will build back over the coastal waters and interact with lower pressure inland tonight through Tuesday. Another frontal system will move across the area waters on Wednesday. High pressure will then rebuild over the coastal waters Thursday before another system approaches over the weekend. Diurnal westerly pushes are expected through the Strait of Juan de Fuca the next several days and could result in small craft advisories for the Central and Eastern Strait Tuesday through Thursday in the evenings. Seas have built over the coastal waters around 5 to 8 ft. Seas will continue to range between 6-8 feet on Monday, before subsiding back towards 4-6 feet Monday night into Tuesday. Seas then look to hover in this range through much of the week. 14 && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$