Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
553 FXUS66 KSEW 182218 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 318 PM PDT Wed Sep 18 2024 .SYNOPSIS...Weak high pressure holds over the region through Thursday with morning clouds but afternoon sunshine. Expect a return to a wetter pattern Friday and again late in the weekend as the next disturbance crosses the region, though considerable uncertainty remains in the pattern by early next week. && .SHORT TERM /TONIGHT THROUGH SATURDAY/...Temperatures are climbing through the 60s this afternoon across western Washington with even a few spots around 70 degrees as the morning cloud cover has continued to steadily scatter out across parts of the region. Will continue to see some lingering cloud cover - especially nearer to the mountains - but the bulk of the drizzle or light rain has now ended. Expect a return of low clouds and some patches of fog again tonight toward daybreak, but another largely dry day is expected on Thursday with temperatures similar to today, or perhaps a couple of degrees cooler in a few spots. A passing upper level disturbance may provide just enough forcing a few light showers in the mountains late in the day Friday, but these shouldn`t amount to much and this impulse will largely just provide a reinforcing push of clouds into the region. A stronger weather system is likely to approach the region late in the day Saturday. While it`ll likely remain initially centered to the north, expect rain chances to return to the far northwestern portions of the area through the day. .LONG TERM /SUNDAY THROUGH WEDNESDAY/...Zonal flow remains in place across the far northeastern Pacific though the weekend, which will continue to maintain precipitation chances across the region. Expect the passing trough to bring a more organized shot of rain (and high mountain snow above 8000 ft or so), and while QPF amounts trended a little higher (around a tenth to a quarter inch in the lowlands and a half inch to an inch for the coast and mountains, highest north), there does remain some uncertainty with respect to where the moisture plume will end up and if it will track more into southern B.C. or more squarely across Washington. As a result, expect to see some fluctuations in the forecast for the next several cycles and hopefully the ensemble guidance begins to come into better agreement. Nevertheless, confidence dips even lower toward the middle of next week with about half of the guidance favoring a ridge bringing a warm up and some drier conditions, but still about half of the guidance favoring an eastern position in the ridge that would leave the region open to a more active pattern and cooler/wetter conditions. Cullen && .AVIATION...Northwesterly flow aloft as weak upper level ridging remains offshore. Conditions have significantly improved since earlier, with bouncing MVFR/VFR ceilings across the area. Expect this trend to largely continue, with ceilings lifting to low end VFR into this evening. With rather light surface flow expected tonight, likely will see a redevelopment of MVFR/IFR patchy fog and stratus throughout most terminals late tonight into Thursday morning. VFR will return around 21-23z Thursday afternoon. KSEA...MVFR conditions early this afternoon will slowly rebound back to VFR by 00z. N/NW winds around 5 to 8 knots this afternoon will become light overnight into Thursday morning. Ceilings will lower once again tonight around 07z-10z to MVFR, with at least a 25% chance of IFR conditions through 16z. Mazurkiewicz && .MARINE...A surface low will continue to shift southward away from our area with benign marine conditions over the coastal water zones this afternoon. A weak surface trough will expand offshore Thursday into Friday which will boost northwesterly winds over the outer coastal waters to small craft advisory levels. Along with northwesterly winds, combined seas will rise to 7 to 9 feet into Friday, highest in the outer coastal water zones. Seas will then decrease to 5 to 7 feet into the weekend, as tranquil conditions return. Mazurkiewicz && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$