The Lightning Thief, Chapter 2

From the text:

The students acted as if they were completely and totally convinced that Mrs. Kerr— a perky blond woman who I'd never seen in my life until she go
on our bus at the end of the field trip—had been our pre-algebra teacher since Christmas.

Who is Mrs. Kerr? How have the other students been manipluated? Why does Percy see the difference?

The freak weather continued, which didn't help my mood. One night, a thunderstorm blew out the windows in my dorm room. A few days later, the biggest tornado ever spotted in the Hudson Valley touched down only fifty miles from Yancy Academy. One of the current events we studied in social studies class was the unusual number of small planes that had gone down in sudden squalls in the Atlantic that year.

We have to question the weather changes and atmospheric events. What is causing the destructive weather?