The Runoff Risk Advisory Forecast (RRAF) map is based on data outputs from the National Weather Service’s Sacramento Heat Transfer Evapotranspiration Model (SAC-HTET) used for flood forecasting. This model takes into account snow accumulation and melt, soil moisture content and forecast precipitation and temperatures to predict the likelihood of surface water runoff displayed as a series of 2km x 2km colored grids across Wisconsin. If the likelihood of runoff is in the low category, the map shows a clear (no color) grid. As the risk of runoff increases, based on modeled conditions, the grids become darker in color with the darkest color indicating the highest risk for surface runoff.
The Wisconsin RRAF map displays the runoff risk not just for the current day, but 72 hours into the future based on precipitation model forecasts. Using the Map Controls on the right side of the page, it is possible to view the Runoff Risk map out up to 5 days. In the winter, the model looks out up to 10 days using the temperature forecast to predict snowmelt. This “look ahead” allows better planning of manure and other nutrient applications. Balancing a relatively conservative estimate of runoff risk with the uncertainties of precipitation and temperature forecasting is essential to having a credible forecast tool.
Today’s Runoff Risk Advisory Forecast isn’t just determined by today’s weather and soil conditions. The forecast for today is looking ahead to the next 3 days to see if runoff triggering events are going to occur. Why? Because manure applied today could easily runoff with tomorrow’s rains!