The Standardized Precipitation Index (SPI) is one of seven indices used by the Massachusetts Drought Management Task Force to determine the level of drought severity. The SPI reflects soil moisture and precipitation conditions. SPI values are calculated monthly using data in the precipitation database. These values reflect “look-back” periods of one month, three months, six months, and twelve months. The SPI values for these time periods are equivalent to the number of standard deviations from normal for precipitation totals for that time period.
Massachusetts SPI Values for December 2014
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