The coldest average month hits in the low 20's.... The summers are always hot and humid, and often DRY. We did ok with getting some grass growing last year, then had it all wiped out in the drought.
Also, the yard gets fairly saturated in the spring- between the thawing snow and spring rains- we get a lot of run-off then because our house is located near the bottom of of hill. More info than you asked for, I know, but I just thought I'd throw anything that might be helpful...