In Chapter 8 of To Kill a Mockingbird, why does Scout think that the world is going to end and on what does Mr. Avery blame this weather?

Scout's response to waking up in the morning after a long
night's sleep and seeing strange objects falling from the sky is probably not unusual
for a small child living in the Deep South. It was her first sight of snow, and she had
no idea what it was.

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"The world's endin',
Atticus!"

It was Jem's first
look at snow as well, but at least he figured out what it was. When the kids went
outside to play in Miss Maudie's yard (they were trying to save the snow in their own
yard), they were harassed again by Mr. Avery. He had already blamed Jem and Scout for
the unusually cold recent weather, telling them that it "was written on the Rosetta
Stone" that children who behaved badly caused the seasons to change. This time he blamed
them on the snow as well, telling them that it was the first time it had "snowed in
Maycomb since Appomattox"--the sight of General Robert E. Lee's surrender of the
Confederate Army of Northern Virginia in 1865.