Water Supply Outlook May 2009

Updated: May 22, 2009

Mountain runoff forecasts (natural volumes for March to September 2009)

Forecasts have increased significantly for the Oldman, Elbow and Highwood River basins since April 1. Forecasts have decreased for the Milk River basin, and are similar to April 1 forecasts for the Red Deer, North Saskatchewan and remainder of the Bow River basin.

Milk River basin Oldman River basin
  • Below average, except below average to average for the Oldman and Waterton Reservoirs
  • Below average to average for May to September, except below average for the Belly and St. Mary Rivers
  • March - April recorded volumes much below average, except slightly below average for the Belly River and Oldman River at Lethbridge
Bow River basin
  • Below average, except below average to average for the Elbow, Highwood and Kananaskis Rivers and below to much below average for the Bow River at Banff
  • Below average for May to September, except below average to average for the Elbow, Highwood and Kananaskis Rivers and below to 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

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. Recorded 2009 volumes are preliminary and subject to change.

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

Mountain snowpack

Snow accumulations measured in the mountains as of May 1, 2009: Mountain snow accumulations have improved significantly in the Highwood River basin and upstream of the Oldman and Waterton Reservoirs since April 1, and were similar to last month in other areas.

  • Oldman River basin: below average to average in the St. Mary and Belly River basins. Average to above average in the upper Oldman and Waterton River basins. of record.
  • Bow River basin: below to much below average except slightly below average in the Highwood River basin. At 3 out of 5 locations upstream of Banff, snow accumulations rank from third to fifth lowest in generally 25 to 30 years of record.
  • Red Deer, North Saskatchewan, and Athabasca River basins: below to much below average in the Red Deer River basin, with the lowest and third lowest values in 30 years of record measured at 2 out of 4 locations. Slightly below average in the North Saskatchewan and Athabasca River basins.
  • Upper Peace River basin in British Columbia: above normal as of May 15, 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.


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 10, 2009 is available here.

Long Lead Precipitation Outlooks

Environment Canada (issued on May 1, 2009): normal temperature and below normal precipitation for the May through July 2009 period

National Oceanic and Atmospheric Administration (NOAA) (issued on May 21, 2009): below normal precipitation and above normal temperatures in southern Alberta, for June through August 2009.

Climate indicators: The NOAA reported on May 7, 2009 that La Nina conditions have ended, and that neutral conditions are expected to persist through the summer and probably the rest of 2009.

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