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Hydrologic conditions

One of the goals of the Program is to achieve target flows based on the current hydrologic condition of the Platte River. This hydrologic condition is calculated using a formula contained in the Program's Water Plan.

View target flows View past conditions summary

December 2018 to February 2019: Normal

Report period: -
Target Flows
  • February 1-14: 1,800 CFS
  • December 1-31: 1,000 CFS
  • February 15-28: 3,350 CFS
  • January 1-31: 1,000 CFS
Approximate date of next update:

October and November 2018: Normal

Report period: -
Target Flows
  • November 16-30: 1,000 CFS
  • October 1-31: 1,800 CFS
  • November 1– 15: 1,800 CFS

August and September 2018: Normal

Report period: -
Target Flows
  • September 16-30: 1,000 CFS
  • August 1-31: 1,200 CFS
  • September 1-15: 1,200 CFS

  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.

  2. The July end-of-month content in Lake McConaughy as a percent of total capacity was 83.1%, equivalent to the 44.5% level of July end-of-month content over the 1947-1994 period.

Hydrologic Conditions Calculation: Hydrologic Conditions Calculation: (0.464 * 0.453) + (0.404 * 0.445) + 0.061=0.451
Hydrologic Conditions Index: 0.552

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.

July 2018: Normal

Report period: -
Target Flows
  • July 1-31: 1,200 CFS

June 2018: Normal

Report period: -
Target Flows
  • June 1-20: 3,400 CFS
  • June 21-30: 1,200 CFS

  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 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 Calculation: Hydrologic Conditions Index = (0.648 * 0.626) + (0.121 * 0.817) + (0.023 * 0.599) + (0.082 * 0.583) + 0.097
Hydrologic Conditions Index: 0.663

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.

May 2018: Normal

Report period: -
Target Flows
  • May 20-26: 3,400 CFS
  • May 1-10: 2,400 CFS
  • May 27–31: 3,400 CFS
  • May 11–19: 1,200 CFS

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

  2. The April end-of-month content of Lake McConaughy was 1,467,900 acre-feet, equivalent to 84.2% of maximum capacity and 25.7 percentile level of the 1947-1994 April percent-of-capacity.

  3. The April end-of-month content of three upper South Platte reservoirs (Antero, Eleven-Mile, and Cheesman) was 186,525 acre-feet, equivalent to the 68.7 percentile level of their 1947-1994 April contents.

  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 62.2 percentile level of 1947-1994 conditions.

Hydrologic Conditions Calculation: (0.601 * 0.629) + (0.271 * 0.257) + (0.031 * 0.687) + (0.252 * 0.622) - 0.065
Hydrologic Conditions Index: 0.561

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.

March-April 2018: Normal

Report period: -
Target Flows
  • March 23-31: 2,400 CFS
  • March 1-15: 3,350 CFS
  • April 1–30: 2,400 CFS
  • March 16–22: 1,800 CFS

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

  2. The mean February Palmer Drought Severity Index for four climate zones in three states (NCDC divisions Colorado #4, Wyoming #8, and Nebraska #1 and #7) was -0.52, equivalent to the 45.6 percentile level of 1947-1994 February conditions.

  3. The February end-of-month content of seven North Platte reservoirs (Alcova, Glendo, Gray Reef, Guernsey, Kortes, Pathfinder, and Seminoe) was approximately 2,125,352 acre-feet, equivalent to the 97.1 percentile level of 1947-1994 end-of-month February conditions.

Hydrologic Conditions Calculation: (0.120 * 0.513) + (0.662 * 0.456) + (0.198 * 0.971) - 0.011
Hydrologic Conditions Index: 0.545

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.