Platte Basin 'hydrologic conditions' calculations, June 2009:

To set the hydrologic condition for June, an index of conditions is computed using four Platte basin variables.  These variables and their corresponding values were as follows:

(1) The mean May streamflow in the Platte River at Grand Island [provisional] was 972 cfs, or at the 27.4 percentile level of 1947-1994 May flows.

(2) The mean May Palmer Drought Severity Index for four zones (NCDC climate divisions Colorado #1, Wyoming #8, and Nebraska #1 and #7) was +0.74, equivalent to the 66.5 percentile level of 1947-1994 May conditions.

(3) The mean May streamflow in the South Platte River at the CO-NE state line [provisional] was 140 cfs, or at the 41.4 percentile level of the 1947-1994 May flows.

(4) The April 1 percent-of-normal snowpack in the North Platte Basin of Wyoming was 102% of normal, equivalent to the 59.0 percentile level of 1947-1994 conditions.

The Index was therefore calculated as follows:

Hydrologic Conditions Index = (0.648 * 0.274) + (0.121 * 0.665) + (0.023 * 0.414) + (0.082* 0.590)  + 0.097

Hydrologic Conditions Index = 0.413

An index value above 0.30 and below 0.70 constitutes "normal" conditions.

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Questions or comments:  donald_anderson@fws.gov