Water Supply Outlook May 2011

Updated: May 12, 2011

Mountain runoff forecasts (natural volumes for March to September 2011)

Volume forecasts have increased by about 5 to 15% in the Red Deer, Bow and Oldman River basins since March 1. The North Saskatchewan River volume forecasts remain similar.

Oldman River basin

Bow River basin

Red Deer River basin

North Saskatchewan River basin

  • Average for the Brazeau Reservoir, Bighorn Reservoir and the North Saskatchewan River at Edmonton
  • Average for May to September
  • March - April recorded volumes much below average for the Brazeau reservoir and the North Saskatchewan River at Edmonton, and average for the Bighorn reservoir

Precipitation can have a major impact on water supply between now and the end of September. The forecasts above assume that precipitation over the remainder of the winter period and through the summer will be normal. The range of possible precipitation scenarios is large however, and as a result, probable range forecasts and a minimal precipitation forecast of natural runoff volume are also provided for each individual basin. Since more information becomes known over time, forecast ranges will narrow over time. Recorded 2011 volumes are preliminary and subject to change.

Check our Forecaster's Comments throughout the month for updated information regarding runoff conditions.

Mountain snowpack

Mountain snow accumulations have improved considerably in the Red Deer, Bow and Oldman River basins since March 1. Snow packs have declined in the foothills and most of the plains areas during April.

Snow accumulations measured in the mountains as of May 1, 2011:

  • Oldman River basin: ranging from average to much above average at all locations
  • Bow River basin: average to above average upstream of Banff and in the Kananaskis, Highwood River and Elbow River basins
  • Red Deer, North Saskatchewan, Athabasca River basins: average to above average in the Red Deer River basin and upstream of the Bighorn Reservoir, Brazeau Reservoir, and in the Athabasca River basin
  • Upper Peace River basin in British Columbia: average to above average as of May 1, as indicated in British Columbia's Snow Survey and Water Supply Bulletin

Mountain snowpack is an important source of water supply to reservoirs in the spring. On average, the accumulation of snow by May 1 is typically at or near the seasonal total.


Contoured maps of precipitation amounts and as a percent of normal for the past month and for current and recent seasons are available here. Maps of precipitation amounts for the most recent day, week and month to date are available here.

Soil Moisture

Alberta Agriculture models soil moisture for non-mountainous, agricultural areas of Alberta. Modelled soil moisture compared to average as of May 3, 2011 is available here.

Long Lead Precipitation Outlooks

Environment Canada (issued on May 1, 2011): Below normal temperatures for central and southern Alberta. Normal to above normal temperatures for north central and northern Alberta. Normal precipitation for southern and northeastern Alberta. Above normal precipitation for central and northwestern Alberta.

National Oceanic and Atmospheric Administration (NOAA) (issued on April 21, 2011): An even chance of below normal, normal, or above normal temperature and precipitation in southern Alberta, for May through July 2011.

Climate indicators : The NOAA reported on May 5, 2011 ENSO-neutral conditions is expected to develop during May-June 2011 and continue through the Northern Hemisphere in the summer of 2011.

Note that forecasting weather for such a long time period into the future is very difficult, and so the historical accuracy has been variable, dependent on location and time period, and is often low, more so for precipitation than temperature. Environment Canada provides an assessment of their forecast method's historical accuracy on their website.

Reservoir storage

Water storage volumes in the major irrigation and hydroelectric reservoirs of the Milk, Oldman, Bow, Red Deer North Saskatchewan, and Athabasca River basins is updated each weekday and is available in the Provincial Reservoir Storage Summary.


Background information on the Water Supply Outlook is available in Frequently Asked Questions

Media Contact:
Communications Division, Alberta Environment
Phone: (780) 427-6267