ha!
I remember when I was there in 2011, it snowed on May 1st (!) .. I just could not believe it.
My office was out at Chodov, outside of Prague and we lived in Prague 1 on Maiselova St, one block from Old Town Square.
I have lived in the SF Bay Area for a long time (since 1987), so I have definitely become a it of a weather wimp. But, I was born and raised in Chicago, so I know snow and cold. But I never recall it snowing in Chicago on May 1st. Geez.
Hope the OP enjoys the CR. Lots of cool stuff to see and plenty of good beer and Becherovka to help you forget about the winter.