Water Supply Outlook May 2012

Updated: May 10, 2012

Mountain runoff forecasts (natural volumes for March to September 2012)

Volume forecasts have generally increased by 5 to 10% in most locations since April 1, except for the Bow River basin which increased or decreased by 5%. The volume increase is due to above normal precipitation throughout most of the province.

Milk River basin Oldman River basin Bow River basin Red Deer River basin North Saskatchewan River basin

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. Streamflow volume forecasts are updated monthly from February to May, and again in July.

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

Mountain snowpack

Snow accumulations measured in the mountains as of May 1, 2012:

  • Oldman River basin: Average to much above average.
  • Bow River basin: Above average to much above average.
  • Red Deer, North Saskatchewan, Athabasca River basins: Above average to much above average.
  • Upper Peace River basin in British Columbia: Above average as of May 1, as indicated in British Columbia's Snowpack and Water Supply Outlook

Mountain snowpack is an important source of water supply to reservoirs in the spring. Accumulation at this time of year typically accounts for about 80-95% of the seasonal total.

Plains Spring Snowmelt Runoff Forecasts (issued in March and April each year)

Plains Snowpack (issued in March and April each year; Cypress Hills mid to late January and February)


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 6, 2012 is available here.

Long Lead Precipitation Outlooks

Environment Canada (issued on April 30, 2012): Above normal temperatures and normal precipitation for central and southern Alberta for the period from May to July 2012.

National Oceanic and Atmospheric Administration (NOAA) (issued on April 19, 2012): An even chance of below normal, normal, or above normal temperatures and precipitation in southern Alberta, for May to July 2012.

Climate indicators : The NOAA reported on May 3, 2012 that La Nina transitioned to ENSO-neutral conditions which are expected to continue through the summer of 2012.

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 and Water
Phone: (780) 427-6267