An analog season is the period from the climate division's history whose precipitation patterns most resemble the period of interest. Only the periods whose dates correspond with the period of interest's dates are considered. In other words, if the period of interest is the 30-day period ending March 21st, all 30-day periods ending March 21st are compared with the period of interest and a "winner" is determined.

The analog season is determined by a combination of three tests:

1. Total Precipitation: This component tests for the period that has the most similar accumulated precipitation. This test addresses the question: How much rain fell during the period?
2. Character of Precipitation: This component tests the number of daily precipitation events exceeding certain thresholds. This test addresses the question: Did the rain fall as many small events or a few larger events?
3. Timing of Precipitation: Depending on the number of days in the period of interest, this component breaks up historical periods into decades (ten equal units of time) or pentads (five) and compares them to the period of interest. Only periods of interest 30 days or longer are subject to this test. This test addresses the question: Did the precipitation occur early or late during the time period?

Arndt Score: The Arndt Score is a numerical indicator of the strength of the "match" between the period of interest and the analog season:

Arndt Score	Interpretation
10.00	Perfect match: Precipitation patterns are identical to period of interest
9.50-9.99	Very strong match
9.00-9.49	Significant match
8.50-8.99	Moderate match
8.00 or less	Weak match: period of interest is unique in history