The map at left shows the average date of the first frost in fall. Use it to help plan when to plant late-season or fall crops, and when you can expect frost-sensitive plants to finally succumb to freezing temperatures.
Keep in mind that t...he dates are guides, and no guarantee that frost will not occur before the first date shown.
Also remember that microclimates have a tremendous effect on frost. Some valleys and low-lying areas can be plagued by early frosts well before the first frost date on cold nights when there is radiational cooling. Large bodies of water may moderate air temperatures at some sites, reducing the chances of frost.