1. Reduction of Streamflow From Upstream Ice Formation a.k.a. “Ice Bite” Brian Connelly North Central River Forecast Center Chanhassen, Minnesota

2. Ice Bite - What Is It? River water temperature is approaching 32°F. River water temperature is approaching 32°F. An ice cover hasn’t formed on the river yet. An ice cover hasn’t formed on the river yet. An extreme cold snap occurs over the course of a few days. An extreme cold snap occurs over the course of a few days. Cold temperatures rapidly generate a stationary ice cover on the river, and freeze some water sources. Cold temperatures rapidly generate a stationary ice cover on the river, and freeze some water sources. Since the river ice is stationary it is removed from the downstream flow, and river levels can drop rapidly. Since the river ice is stationary it is removed from the downstream flow, and river levels can drop rapidly.

3. Ice Bite – Who Cares? Low water event, not flooding Low water event, not flooding An ice bite can have temporary but significant impacts on navigation, municipal water supplies, and power plant operations. An ice bite can have temporary but significant impacts on navigation, municipal water supplies, and power plant operations. River levels typically rebound somewhat after a few days. River levels typically rebound somewhat after a few days.

4. Ice Bite Example St. Louis, Missouri – January, 2003 St. Louis, Missouri – January, 2003 Lower than normal precipitation during summer and fall of 2002 Lower than normal precipitation during summer and fall of 2002 Low water entering winter season Low water entering winter season Concern over navigation Concern over navigation

5. Upper Mississippi Air & Water Temperatures

6. Approximate River Ice Cover Before Event

7. Approximate River Ice Cover After Event

8. Air Temperature & St. Louis Stage

9. Forecasting Ice Bite Monitor Conditions Monitor Conditions Significant portion of river must be ice free Significant portion of river must be ice free River water temperature must be at or near freezing River water temperature must be at or near freezing Watch air temperature forecasts for prolonged cold snaps Watch air temperature forecasts for prolonged cold snaps Rule of Thumb Rule of Thumb Flow reduced by 50% Flow reduced by 50% Rebounds to about 75% of original flow Rebounds to about 75% of original flow Source: Wise forecaster from the NCRFC Source: Wise forecaster from the NCRFC

10. Flow Reduction Rule of Thumb

11. Conclusions Process isn’t modeled, but it may be possible to predict using an approach similar to some of the ice jam prediction methods. Process isn’t modeled, but it may be possible to predict using an approach similar to some of the ice jam prediction methods. Potential RFC Forecaster Aids Potential RFC Forecaster Aids Plot latest water temperature observations spatially. Plot latest water temperature observations spatially. Plot latest ice cover/thickness observations spatially. Plot latest ice cover/thickness observations spatially. Plot forecast freezing degree days spatially. Plot forecast freezing degree days spatially. Refine the rule-of-thumb Refine the rule-of-thumb