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Palmer Hydrological Drought Index for May, 1930-1999, for southeastern Idaho. Data source: National Climate Data Center.

Palmer Drought Hydrological Index is a monthly index that is generated that indicates the severity of a wet or dry spell. This index is based on principles of a balance between moisture supply and demand. The index ranges from −6 to +6, with negative values denoting dry spells and positive values denoting wet spells; there are a few values in the magnitude of +7 or −7. This is a hydrological drought index used to assess long-term moisture supply. For further information about this index, check the National Data Center web site (www.ncdc.noaa.gov).

Number of days in June and July, 1967-1997 at Grays Lake, Idaho, that had severe frosts (<30 degrees F).

Hard frosts (<30 F) in June and July can kill small tender plants and small terrestrial invertebrates that may be important in the diet of sandhill cranes or other birds. Thus these patterns may be of interest to those investigating food resources available to birds in the basin.