NASA’s Scientific Visualization Studio has a couple of graphics showing changes in the frost-free regions of the US for March and April. The graphics clearly show the expansion of frost-free areas in the Midwest and Great Lakes during those months, although they have more limited value for us in the Southeast. It would have been helpful for us to have a similar map for earlier in the season, since most of the Southeast is already past the last frost date by March 20, the date of the first image. But I think you can see that with the warmer temperatures we have experienced since the 1970’s, the period between last and first frost is increasing, leaving us with a longer growing season. Some work I did with Melissa Griffin of Florida State University indicates that for every 1 degree F increase in average temperature, the growing season increases by a week to ten days. You can view the graphics at https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4154. Of course, it is also important to keep in mind that these are average conditions and the actual last frost date could be earlier or later than this in any given year. With neutral conditions likely to be in place by February, I think our chance of a late frost is somewhat higher than normal this year.
