• Air temperature data are normally readily available from both climatological and operational hydrometeorological networks.
• It has been shown in many studies that air temperature is probably the best single index to areal snow cover energy exchange.
  

Other variables have been used as indices to snow cover energy exchange.
Net radiation is a good index to energy exchange at a point.
However, net radiation is highly dependent on the surface over which it is measured.
Thus, it would be extremely difficult, in most cases, to extrapolate point measurements of net radiation to determine an areal estimate.
In addition, net radiation is measured at only a few research sites in the U.S.
Incoming solar radiation, vapor pressure of the air, and wind speed have also been used as indices to snowmelt in conjunction with air temperature or net radiation.
However, these variables have not proven to be good indices to snowmelt when used by themselves.