The lack of precipitation for most of the state remains the main story this growing season. The featured chart displays a couple of precipitation metrics for Des Moines. Each point on the x-axis represents the period from that date to August 13th. The orange, green, and black lines represent precipitation totals over the period of days. The blue line is the standardized precipitation index (SPI), which expresses a departure from average in terms of standard deviation. For Des Moines, the SPI is most negative since late May. Rewording , the most significant precipitation departures have been over the period from late May to today.

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Tags:   spi