These maps are provided to help reduce the risk of runoff losses following nutrient/manure applications or other land management activities. The likelihood of runoff from rainfall within the next 5 days or snowmelt within the next 10 days is shown for every National Weather Service (NWS) basin in Wisconsin. There are 214 NWS basins, with an average area of 292 square miles. The risk levels shown represent predictions for expected conditions across these large areas, not for specific fields within the basin.
Maps are updated with NWS forecasts twice a day (approximately noon and midnight).
Jump to: Winter Maps Available Popup Boxes Assessing Risk
Interpreting The Map
Rainfall runoff risk for the next 3 days:
Low - no runoff predicted within the basin.
Moderate – low volumes of runoff predicted for some areas within the basin
High – runoff predicted for most of the basin
We offer 3 forecast maps (today, tomorrow, and the day after that). Each map displays the 3-day outlook for rain runoff risk; in winter, the maps also feature the 10-day snowmelt outlook.
There are three small radio buttons just above and to the right of the map:
Click the one for tomorrow’s date, and the map will update to show the risk level for each watershed starting with tomorrow and looking three days into the future (i.e., four days from today). Clicking on the radio button for two days from today will update the map to show the risk level for each watershed starting two days from today and looking three days into the future (five days from today). Keep in mind that there is more uncertainty to the rainfall and subsequent runoff predictions as you look further ahead.
For example, for the example shown above:
- Clicking the leftmost button displays the composite risk for May 23, 24, and 25
- Clicking the middle button displays the composite risk for May 24, 25, and 26
- Clicking the rightmost button displays the composite risk for May 25, 26, and 27
Runoff risk for the next 10 days:
Winter risk - soils in the basin are frozen or snow-covered, runoff is not yet in the forecast but applications should be made with caution due to limited soil contact and infiltration.
High risk - runoff is forecast within the next 10 days (most likely because of rain), with no snowmelt alert.
High risk - snowmelt is predicted within 10 days leading to runoff within the basin. Rain may also be in the forecast; examine the pop-up box for the basin for more details.
Click on a watershed of interest. A pop-up box will appear that displays:
- Watershed name and National Weather Service station identifier.
- The three-day (or ten-day, in winter) runoff risk level. This level coincides with the coloration on the map. In winter, when the forecast is looking out ten days, the date of the earliest forecast runoff event is displayed.
- Forecast precipitation for each day. The NWS supplies us with precipitation forecasts for each watershed. Although the data are already factored into the runoff calculations, they may be useful guides as you assess risk.
- Single-day runoff risk level. Rather than looking at the maximum predicted runoff over the forecast period, the runoff predicted for each day is compared to the basin threshold to determine the day's runoff risk level for each day. Keep in mind that there is more uncertainty to the rainfall and subsequent runoff predictions as you look further ahead.
If there is snowmelt predicted in the watershed in the next ten days, a snowmelt alert is displayed. In addition, we report if the runoff risk for any given day has any snowmelt component. This allows you to modulate your risk assessment based on what you see in your fields. If all the forecast runoff risk is due to snowmelt and there is no snowpack on or near your fields, your risk assessment may be different from someplace elsewhere in the watershed with significant snow cover.
These maps are based on a NWS basin flood forecast model. Cropped fields are much smaller than the basins and can vary considerably within a basin. Local characteristics can significantly affect the model’s applicability to a given field. Always apply your own knowledge of the landscape when assessing the risk of runoff for your fields. Considerations include:
Risk increases with soil moisture
The model assumes watershed-wide average conditions for soil moisture. If you know that your fields are particularly wet (for example, you experienced a recent rainfall event that was greater than in other parts of the watershed) you should know that the risk of runoff from your fields will be higher than what is shown on the risk map. The opposite may hold true if you estimate that your soil moisture values are lower than the watershed-wide average.
Even if the map shows low risk of runoff, your fields may not be dry enough to spread
Applying liquid manure (typically equivalent to 1/3 to 1 inch or more of rainfall) to wet fields can lead to direct manure runoff, even if the field is otherwise a low risk site due to low slope or low P-index. Make sure your fields are dry enough to accept additional moisture. If liquid manure should runoff or pond in a field or discharge into tile lines, application must stop until the runoff can be checked. Additionally, operating field equipment on wet fields can lead to soil compaction which can greatly reduce crop yields.
Liquid manure applications increase soil moisture
An application of 27,000 gallons per acre of liquid manure is the equivalent of adding approximately 1 inch of water to your fields. A liquid manure application effectively increases your soil moisture, and therefore the risk of runoff from fields receiving liquid manure will be higher than what is shown on the risk map.
Snow-covered and frozen fields are high risk
The model assumes watershed-wide average conditions for snow cover. If you have snow in your fields but the map does not show winter conditions, you should know that the risk of runoff from your fields will be higher than what is shown for the basin. The opposite may hold true if the model shows snow across the basin but there is none in your fields.
Some fields are always higher risk areas
These are areas of concern on your farm, and might include fields with higher slopes, tighter soils, poor drainage, or close to sensitive features such as ponds, streams, lakes, wetlands, sinkholes, etc. Many of these areas may be identified in your nutrient management plan and/or 590 nutrient-restriction maps. You should use caution when applying manure or any agrichemical products in these areas, regardless of what the risk map indicates.