Water Supply Outlook May 2010

Updated: May 12, 2010

Mountain runoff forecasts (natural volumes for March to September 2010)

Forecasts have increased significantly for the Oldman, Spray and Highwood River basins since April 1. Forecasts have decreased for the Milk and Red Deer River basins. The North Saskatchewan River basin volume forecasts remain similar.

Milk River basin

Oldman River basin

Bow River basin

  • Below average for the March to September 2010 period, except below to much below average for the Bow River at Calgary and much below average for the Bow River at Banff
  • Below average for May to September, except below to much below average for the Spray and Cascade Reservoir inflows and the Bow River at Calgary, and much below average for the Bow River at Banff
  • March - April recorded volumes highly variable, click link to see table

Red Deer River basin

North Saskatchewan River basin

  • Below average for the Brazeau Reservoir, below to much below average for the Bighorn Reservoir and the North Saskatchewan River at Edmonton
  • Below 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 to above 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. Streamflow volume forecasts are updated monthly from February to May, and again in July. Recorded 2010 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 Elbow and Highwood River basins and much of the Oldman River basin since May 1. Snow packs have declined in the foothills and most plain areas during April 2010.

Snow accumulations measured in the mountains as of May 1, 2010:

  • Oldman River basin: below to much below average in the St. Mary River, near average in the Waterton and highly variable upstream of the Oldman Dam
  • Bow River basin: below to much below average upstream of Banff and in the Kananaskis and Highwood River basins, and below average in the Elbow River basin
  • Red Deer, North Saskatchewan, Athabasca River basins: below average in the Red Deer River basin and upstream of the Bighorn Reservoir, below average to average upstream of the Brazeau Reservoir, and near average in the Athabasca River basin
  • Upper Peace River basin in British Columbia: below normal 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. On average, the accumulation of snow by May 1 is typically at or near 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 4, 2010 is available here.

Long Lead Precipitation Outlooks

Environment Canada (issued on May 1, 2010): Temperature normal for most of Alberta for May-July 2010 except below normal in the southeastern corner of the province, and above normal across northernmost Alberta. Precipitation above normal except for below normal to normal precipitation in northmost Alberta.

National Oceanic and Atmospheric Administration (NOAA) (issued on April 15, 2010): An even chance of below normal, normal, or above normal temperature and precipitation in southern Alberta, for May through July 2010.

Climate indicators : The NOAA reported on May 6, 2010 that a transition to ENSO-neutral conditions is expected by June 2010, which will continue into Summer 2010.

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