Data for the Clock. The forecasts generated by our Minnesota Lakes Ice-Out Clock are based on statistical analyses of past National Weather Service (NWS) weather data, ice-out dates recorded by the Minnesota Department of Natural Resources (MNDNR), lake location and size data from the MNDNR, and current season weather information from the NWS. Data back to the winter of 1963-1964 were included in the forecasts. 

Accuracy. 

• Forecasts give the most likely ice-out date at the time of the forecast. 
• Late-winter forecasts will be closer to the actual ice-out date than earlier forecasts. 
• The accuracy of all forecasts depends on the specific local weather that occurs between the date of the forecast and the date of ice-out on each lake. 
• Because our data come from NWS airport weather stations, forecasts for lakes closer to an airport weather station will have greater accuracy than lakes farther away from a station. 

Snow. Forecast ice-out dates will be 1-2 days later for every foot of accumulated snow on a lake. Lakes in the northern half of the state may be a few days later than forecast while lakes in the southern half will be a few days earlier than forecast.

Degree days. We need to explain some science jargon. This clock uses “degree days,” which are measures of how cold (Freezing Degree Days) or warm (Thawing Degree Days) a location is. It’s helpful to remember that you can have more than one degree day in a 24-hour period. Degree days are the difference between the daily temperature mean (high temperature plus low temperature divided by two) and 65°F.

Degree days for a single (24-hour) day are calculated using the following formulas:

• Thaw Degree Days for a single day: [(High temp + low temp)/2] -32
• Freezing Degree Days for a single day: 32- [(high temp + low temp)/2] = FDD
• If the result of the formula is a negative number, then the answer is zero (0).