How to Use the Map

To determine the likelihood of a freeze in a particular area, first locate the area on the freeze map.  The lines on the map indicate the mean date for the freeze; if the area in question is between lines, it is possible to interpolate with an accuracy of one or two days.

The mean date is the 50-percent probability date.  This date is convenient for reference, and for comparing one area with another.  Although the mean dates of freezing are used most often, frequently it is important to know probabilities other than 50 percent.  For example, if a farmer plans to transplant tomatoes on the mean freeze date, he is taking a 50-percent chance there will be no freeze after that date.  Generally 50 percent is too great a risk, but if he waits until all danger of a freeze is past, the planting date may be too late for best results.  In most situations, the acceptable level of risk is somewhere between 50 percent and 5 percent.

To find the dates for other probability levels, refer to the map legend and apply the proper correction.  The probability levels given in the legend refer to the chance that a freeze will occur after the date indicated.