Did You Know?
In order to place each month and season into historical context, NCDC assigns ranks for each geographic area (division, state, region, etc.) based on how the temperature or precipitation value compares with other values throughout the entire record when sorted from highest to lowest value. In other words, the numeric rank value within the area represents the position or location of the sorted value throughout the historical record (1895-present). As a year is added to the inventory, the length of record increases. As of 2015, NCDC has 121 years of records. Thus a rank of 121 would represent the warmest or wettest on record; a rank of 1 would represent the coolest or driest on record. If a state has a rank of 109, then it would be the 13ᵗʰ warmest or wettest on record. If a state rank has a value of 13, then that state ranked 13ᵗʰ out of 121 years, or 13ᵗʰ coolest or driest.
The "Below Normal", "Near Normal", and "Above Normal" shadings on the color maps represent the bottom, middle, and upper tercile (or three equal portions) of the distribution, respectively. The lowest and uppermost decile (or 10%) of the distribution are marked as "Much Below Normal" and "Much Above Normal", respectively. In other words, for a 121-year period (1895-2015), a rank of Much Above/Below Normal, would be in the top/bottom 12 on record. Below/Above Normal, would represent one of the 40 coolest/warmest or driest/wettest such periods on record. "Near Normal" would represent an average temperature or precipitation value that was not one of the 40 coolest/warmest or driest/wettest on record. For a 121-year period of record, "Near Normal" would represent a rank between 41 and 81.