minor parameters
- TIPM
- The antecedent temperature index (ATI) is an index to the temperature of the surface layer of the snowpack.
TIPM indicates the thickness of the layer being considered.
It is recommended that a value of TIPM of 0.5 or greater be used in areas which typically have a relatively shallow snow cover like most of the upper midwest portion of the U.S.
For areas which generally have a deep snow cover, a value of TIPM in the range of 0.1 to 0.2 would be appropriate.
- MBASE
- A melt base temperature of 0oC has proven to be completely adequate in the vast majority of watersheds.
An initial value of MBASE other than 0oC could be justified in the case of a heavily conifer-forested area.
Since most climatological stations are located at relatively open sites, the measured daytime temperature is generally warmer than the temperature beneath a dense forest canopy.
The use of a value for MBASE of 0.5 to 1oC is one way to compensate for this difference.
- PXTEMP
- Various studies have shown that the temperature at which precipitation is equally likely to be rain or snow typically is in the range of 0 to 2oC.
Thus, a good default value for PXTEMP is 1oC.
- PLWHC
- The percent liquid-water-holding-capacity for ripe snow has been found to be on the order of 2 to 5 percent.
Thus, the parameter PLWHC would be in the range of 0.02 to 0.05.
PLWHC should be somewhat greater for fresh snow.
However, it is hard to determine the liquid-water-holding-capacity of fresh snow because by the time drainage ceases, the snow has become ripe.
Ripe snow is snow that is at 0oC and has liquid-water holding capacity satisfied.
Runoff from snow cover cannot begin until the snow cover is ripe.
- DAYGM
- Ground melt occurs when the soil is not frozen.
The amount of ground melt usually decreases throughout the snow season as the soil temperature drops.
The parameter DAYGM is an average daily ground melt during a typical winter.
Typical values for DAYGM vary from 0.0 mm for areas which typically have frozen ground to 0.3 mm for areas with relatively mild climates and yet deep snow covers.