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 10-day snow 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