Second '96 Outage

In an article called Power Outage Darkens West, Matt Drudge reported that a second massive power outage had occurred on August 10, 1996.

3:48 PM PT the electricity snapped.
Over 15 million without power
A massive power outage has struck a widespread area of California, with reports of lost electricity coming in from as far as the Mexican border to Oregon and as far east as Nevada, New Mexico and Texas.
Power has been cut from San Diego to Bend, Oregon and east to Tucson, Arizona and to the Texas panhandle.
The outage appeared to be intermittent, affecting some areas, with others getting power back quickly.
This marks the second massive power outage in as many months. The source of the electrical breakdown is not known.

Comments on the Internet regarding this second outage show that like the first massive power outage, this one did not have a believable explanation, nor did the outage affect only the US.

10 Aug 96: Power is back on in Phoenix for many. Some never lost it and some still waiting.
10 Aug 96: CNN on-line reports 5 western states affected, some areas flickered, some still without power at 8 PM... New Mexico, Arizona, Nevada, Cal, and Oregon. Power service spokesman, I believe from, Las Vegas, says that it is probably weather related, read too much AC, but not weather caused.
11 Aug 96: Major power companies on the west coast are reporting that a fire in CA took out a single communications line which caused blackouts in six states. Power was out for ten hours or more in some areas.
12 Aug 96: Our Australia news network, the last I heard of it, did not report the cause of the power outage in USA. Coincidentally, Malaysia was reported to have suffered a blackout (the biggest of its kind) to the whole country (Both Peninsular and eastern islands!) just last Saturday. That outage lasted more than 12 hrs and officials are still investigating the incident with assistance from an external consultant party.
12 Aug 96 The power outage did affect Vancouver, WA as a blackout in some areas. In Portland, we had a serious brownout, lights went real dim, fans would not turn. The explanation I heard was that down in another state somewhere I forget, the weather was so hot that the lines expanded and sagged low enough to touch the tops of the trees, which caused a short. The part I don't buy is that part where the lines could expand and sag that much, because I know they know how to prevent that.
13 Aug 96: Writing in from Fresno, CA. The scuttlebutt here is that the overall instability in the Pacific Intertie is nowhere near being cured or stabilized. We might expect another large power outage or few because of the high heat and any grid anomaly (such as a squirrel, forest fire or windstorm shorting the line during high demand). Central California is facing 2 more days of 110 degree heat (10 degrees above normal).

An explaination of sorts was given by California's PG&E, as reported by the San Francisco Chronical on August 27, 1996.

Two million Pacific Gas and Electric Co. customers would have been spared from the August 10 blackout if employees of an out-of-state power supplier had recognized and flagged the early signs of impending trouble, state regulators were told yesterday. ... The utility company was never warned that major transmission lines of the Pacific Intertie network had shorted out in Oregon, causing "islands" of outages in California and eight other western states. ... The circumstances of the August 10 outage are still being investigated. It appears, however, that the blackout was caused by a series of events.

Operators of the system got their first warning at 2:06 PM when a 500,000-volt transmission line in northern Oregon shorted out after sagging into a tree. About 46 minutes later, another 500,000-volt line went down for the same reason. ... About an hour later, two more high-voltage lines were shorted, again by lines sagging into trees, this time combining to "trip" a large power plant and cause the loss of 860 megawatts of power in 73 seconds. The rapid power loss caused the Intertie line to shut down, prompting automatic sensors to break transmission circuits at the Oregon-California border and other key points throughout the West.

[An] emergency meeting of the California Public Utilities Commission, [was] called to explore the reliability of the high-voltage transmission network, which serves 59 million people in 14 western states, two Canadian provinces and parts of northern Mexico.