I’ve posted about this broad idea before.  Here in the Central Valley, the transition from summer to winter happens very fast.  And, it happens in October.  What I think is especially cool about October is that the ‘Normal High” for the first of the month is the same as the ‘Record High’ for the last of the month.  The ‘Record High’ drops over 20 degrees from 10/2 to 10/28.  Neat.