Probability Charts
Probability Curves charts by station
The Heat Index Probability Charts are a collection of graphs that display the probability of a given heat index occurring on, before, or after a given day of the year for a given location. These graphs are available for hundreds of stations across the United States. They represent decades of data that have been aggregated and computed to provide information on the frequency of occurrence of heat indexes ranging from 80-115°F.
The probability that a given heat index would occur on, before, or after a given date was computed using a simple climatological probability calculation (specifically, the number of years where a specific heat index value was reached on, before, or after that date divided by the total number of years of data available). As these data were subject to large amounts of noise, resulting in graphs that were difficult to interpret, smoothing was performed by taking a 30-day moving average. The result is an estimation of the probability of a range of heat index occurrences using climatological observations.