Last Expected Frost Date

Trying to figure out when the first expected frost in your area will be can be frustrating.  The problem is that no one knows for sure.  Everyone is guessing - some using historical weather data, others not.  A good bit of the information that I found is old, whether it be taped to a desk at the Master Gardener's office or online in a 1988 NOAA report.  Another source I have for this information is Gardening in the Carolinas by Bob Polumski.  I'm going to lay out some of this information and let's see if we can reach a consensus.

MG Office - Average First and Last Frost Dates
Charleston Airport     November 20th     March 15th

NOAA - 50% Frost Chance Table
50% chance of Frost on or after the spring date indicated
50% chance of frost on or before the fall date indicated
Charleston AP            November 12th     March 18th

NOAA - 10% Frost Chance Table
10% chance of Frost on or after the spring date indicated
10% chance of frost on or before the fall date indicated
Charleston AP            October 30th         April 6th

Gardening in the Carolinas by Bob Polomski
average date of first fall freeze 11/21
average date of last spring freeze 3/11 or 3/16

What does all of this mean?  Let's start with the MG office information.  First of all, I don't know the source.  I believe it to have been reliable when it was taped to the desk, but I can't say when that was, but the dates are in the ballpark.  The info in the Polomski book is a little dated, but it's also a little hard to interpret.  Like the MG office, it's an average, but it's also a couple of graphics of NC and SC with wavy lines.  Once again, these first and last average frost dates are in the ballpark - see for yourself.

When I first started writing this, I wanted a clear answer - the NOAA information seemed too vague.  But now that I've reached this part of the article, it makes the most sense.  No one is going to know for sure when it will freeze, until it does, but the table gives a good estimate.  On November 12th, you should be planning on it to freeze, if it hasn't done so already.  The same thing goes in the spring - by April 6th there is very little chance that it will freeze again.  Like I've said before, none of this is exact, but it's the best we've got - unless you want to go by the farmer's almanac.