is there a website that tells you the high and low temperatures for the months past?

Answer 1

It depends on where you're at, but the first place I'd check if you're in the US is your local National Weather Service office site. You can find the offices at http://www.nws.noaa.gov/organization.php
Each one usually has a local climate page with archived temperatures for its area of responsibility.

Answer 2

try weatherunderground.com

Answer 3

www.weather.com