(Larger version of the “after” graphic can be seen here)
We’re at the WSDOT event announcing the dates for the nine-day Alaskan Way Viaduct closure, and here they are: October 21-31. That spans two weekends and one workweek; here’s the official news release. But it’s not a complete closure of the entire stretch the entire time – here are the details, from WSDOT (and you can see a map here):

Northbound viaduct closure details

Northbound SR 99 between the West Seattle Bridge and South Royal Brougham Way will be closed around-the-clock beginning at 7:30 p.m. Friday, Oct. 21 to 5 a.m. Monday, Oct. 31.
Northbound SR 99 between the South Royal Brougham Way on-ramp and the Battery Street Tunnel will open from 5 a.m. to 7 p.m., Monday through Friday, and for special events at CenturyLink Field.

Southbound viaduct closure details

Southbound SR 99 between the Battery Street Tunnel and West Seattle Bridge will be closed around-the-clock beginning at 7:30 p.m. Friday, Oct. 21 to 5 a.m. Monday, Oct. 31.

When 99 reopens on Halloween, a “construction bypass” will be in place, and WSDOT has just released this video of how that will work:

We also have just talked with SDOT – the new 1st Ave ramp to/from the westbound Spokane Street Viaduct will NOT be finished before the October closure, though SDOT’s Bob Powers says it is expected to be done “by the end of the year.” (added) Here’s our 2-minute chat with him, starting with our question about the new 1st ramp, continuing to “so, city advice for getting around?”

He also says (if you missed it in the clip) 1st Avenue South will be open, two lanes each way, under the Spokane St. Viaduct, for the Alaskan Way Viaduct closure period. (We would also add that the 4th Avenue offramp from the eastbound bridge is usually an excellent Viaduct alternative for getting into downtown – we used it a lot in the mornings while covering the Bushaw murder trial, and it still seems underutilized.)

Metro says it will be adding trips to some West Seattle routes as of October 1st, particularly the 54, which will be on an every-15-minute schedule. The West Seattle Water Taxi will NOT have a schedule change because of the closure, but will continue on through the fall and winter again this year, thanks to state “mitigation” funding related to the ongoing Highway 99 construction.

P.S. We asked Metro reps about the fate of the 2nd/Columbia westbound bus stop – you’ll recall they asked for comments regarding a potential permanent closure. It will be closed for the duration of the October Viaduct shutdown, since southbound 99 will be entirely off-limits. Its permanent fate hasn’t been decided yet – but they tell us that 70 percent of the comments they received were in support of keeping it open. Once 99 has the SODO detour in place, they have to figure out, we are told, what’s the fastest corridor for buses to travel.