Glenn is blogging it in real-time... keep checking for updates.
UPDATE: probably not terrorism, and ConEd reports that smoke at one of their plants was not from a fire, just part of normal shutdown (I'd hate to imagine what an abnormal shutdown would be like :)
Theories: Sunspot activity?
SUNSPOT WATCH: Sunspot 431 is growing fast. During the last 24 hours it has swollen four-fold in area, and now poses a threat for X-class solar flares.
or just a really hot day? (today's temp map shows 100-degree weather over the entire continental US).