May 1-31, 2018

May 2018
Normal

Target Flows

  • May 1 - 10 : 2400 CFS
  • May 11 - 19 : 1200 CFS
  • May 20 - 26 : 3400 CFS
  • May 27 - 31 : 3400 CFS

Variables and Values

  1. The mean April streamflow in the Platte River at Grand Island was 2,055 cfs (provisional USGS data), or at the 62.9 percentile level of 1947-1994 April flows.

Hydrologic Conditions Index
0.56

The threshold index value is 0.30 for "normal" conditions and 0.70 for "wet" conditions. The current index value is greater than 0.30 and less than 0.70 and constitutes "NORMAL" condition.

Hydrologic Conditions Calculation
(0.601 * 0.629) + (0.271 * 0.257) + (0.031 * 0.687) + (0.252 * 0.622) - 0.065

March 1 - April 30, 2018

March-April 2018
Normal

Target Flows

  • March 1 - 15 : 3350 CFS
  • March 16 - 22 : 1800 CFS
  • March 23 - 31 : 2400 CFS
  • April 1 - 30 : 2400 CFS

Variables and Values

  1. The mean February streamflow for the Platte River near Grand Island gage (provisional USGS data) was 1,710* cubic feet per second, equivalent to the 51.3 percentile level of 1947-1994 February conditions. (*The USGS streamflow gage at Grand Island reported "ICE" conditions for the entirety of February.  Data from the Overton gage was used as a surrogate)

Hydrologic Conditions Index
0.55

For this period, the threshold index value is 0.25 for "normal" conditions. The current index value is less than this and constitutes "NORMAL" conditions.
 
Note that for the March-April period, there are only "dry" and "normal" designations because "wet" targets are the same as "normal" targets for this period.

Hydrologic Conditions Calculation
(0.120 * 0.513) + (0.662 * 0.456) + (0.198 * 0.971) - 0.011

June 1-30, 2018

June 2018
Normal

Target Flows

  • June 1 - 20 : 3400 CFS
  • June 21 - 30 : 1200 CFS

Variables and Values

  1. 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 was 1,883 cfs (provisional USGS data), or at the 62.6 percentile level of 1947-1994 April 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 2.13* equivalent to the 81.7 percentile level of 1947-1994 May conditions.
    3. The mean May streamflow in the South Platte River at Julesburg (CO-NE stateline) was 412 cfs (provisional data), equivalent to 59.9 percentile of 1947-1994 May flows.
    4. The April 1 percent-of-normal snowpack in the North Platte Basin of Wyoming* (seven specific NRCS locations) was 101.4% of normal, equivalent to the 58.3 percentile level of 1947-1994 conditions. 
Hydrologic Conditions Index
0.66

For this period, the threshold index value is 0.30 for "normal" conditions and 0.70 for "wet" conditions. The current index value is greater than 0.30 and less than 0.70 and constitutes "???" conditions.

*based on temporary weekly PDSI data, to be updated when monthly PDSI data is available.

Hydrologic Conditions Calculation
Hydrologic Conditions Index = (0.648 * 0.626) + (0.121 * 0.817) + (0.023 * 0.599) + (0.082 * 0.583) + 0.097

August 1 - September 30, 2018

August and September 2018
Normal

Target Flows

  • August 1 - 31 : 1200 CFS
  • September 1 - 15 : 1200 CFS
  • September 16 - 30 : 1000 CFS

Variables and Values

  1. The mean July Palmer Drought Severity Index for two climate stations in Nebraska (NCDC Nebraska Divisions 5 and 8) was 1.32 equivalent to 45.3% of the 1947-1994 July conditions.

Hydrologic Conditions Index
0.55

For this period, the threshold index value is 0.29 for "normal" conditions. The current index value is greater than this and constitutes "NORMAL" conditions.
 
Note that for the August-September period, there are only "dry" and "normal" designations because "wet" targets are the same as "normal" targets for this period.

Hydrologic Conditions Calculation
Hydrologic Conditions Calculation: (0.464 * 0.453) + (0.404 * 0.445) + 0.061=0.451