We calculate the snow forecast summary by taking the snow forecast for the previous night + the current day. The summary calculation is shown this way since this is the snow that you would see/ski on that day.
In the following example for Jackson Hole, the snow forecast summary has 12 inches for Friday.
If you then scroll down to the Daily Forecast section, we have 5-9 inches for Thursday night and 3-7 inches for Friday during the day.
Thursday Night = 5-9 inches = 7 inches
Friday Day = 3-7 inches = 5 inches
Friday Summary = 12 inches
View → Jackson Hole Snow Forecast