Update 10:40pm
The last remaining pockets of customers without power were finally taken care of by diligent City Light crews who worked into the evening to restore it. There were about 13 north of Madison Middle School and a roughly two block area near the Morgan Street Junction that still had no electricity well into the evening after being off since around 10am.

Update 7:45pm
Persistent pockets of outage continue into the evening with 13 customers north of Madison Middle School still without power and readers are reporting that another outage extends from 40th almost to 42nd S.W. and a couple of blocks in both directions from Fauntleroy. This outage does not appear on the City Light System status map.

Update 3:15pm
13 customers are due to get their power back shortly as the last of those without it from the power outage that began at around 10am when a branch from fir tree affected the power lines at 46th and Hanford Streets S.W. At its peak the outage left 10,900 City Light customers without electricity. The outage affected businesses on the West side of Calfornia from the Admiral District south and down to near White Center in what appeared to be a cascading series of outages as the number kept fluctuating over the course of the day. West 5, Cafe Nouveau, West Seattle Thriftway and many others reported outages and had to deal with the aftermath.

Update 1:55pm
The number of people still without power has dropped to 758 as of 1:55pm. Those were concentrated just north of Madison Middle School in the Admiral District. Crews expect to have it back on within the hour.

Update 1:30pm
Crews from City Light continued to make repairs on the pole and wiring at 46th S.W. and S.W. Hanford Street as the number without power dropped to 4250 as of 1:30pm. They expect to have the remaining customers to be back in service by 3:30pm

Update 1:05pm
Power was still out for 10,899 City Light customers in West Seattle as the expected restoration time came and went but sporadic reports of power coming back were coming in to the Herald. Many users of the Comcast internet service also reported outages and those too were reported to be sporadic.

Update 11:15am
The number of customers affected continued to grow as a major power outage struck West Seattle on Monday Dec. 30. The most recent number was 10,922 without electricity. The cause was determined to be a tree branch fall. A tree branch fell into power lines near SW Hanford and 46th Ave SW.
A Google Maps view shows that major, cross peninsula power lines run east-west along Hanford Street.

The Seattle City Light System Status map here http://www.seattle.gov/light/sysstat/ shows the rough outlines of the outage.
Restoration is expected within two hours or by 1pm.

Update 10:43am
The number and area affected by the power outage has expanded to nearly 10,300 and extended down to Alki Beach. It's now reported to be 10 total outages on the peninsula. No cause yet determined.

Update 10:15am
Seattle City Light has revised the total customers affected (or at least shows a disparity between their tweets and number listed on their system status map) showing that more than 5700 customers are without power. The power outage extends from Alki Point to White Center, Puget Sound to the Duwamish they said. It's actually four outages at different locations but they apparently are linked.
The cause is not known at this time.

Original Post

City Light has reported that a power outage has affected nearly 11,000 City Light customers in West Seattle. No detailed information yet but reader reports indicate the area affected is north of the West Seattle Junction over to Avalon Way S.W.

The Seattle City Light System Status map shows nothing as of 10:04am but City Light said it can take some time to get the full extent of an outage to appear there. See that map here: http://www.seattle.gov/light/sysstat/

We will update as we get more information.