|All aspects at upper-elevations in the Wasatch Mountains are presently|
snow covered (Source: Alta Ski Area)
|Typical values of the surface energy budget|
components (Watts/square meter) at midnight and
noon (Whiteman 2000)
In the midlatitudes under clear skies, the net all-wave radiation reaches a peak near local noon when the incoming shortwave radiation is largest, but is negative overnight when the shortwave radiation is near zero and more long-wave radiation is emitted by the Earth's surface than is received from the atmosphere. This is well-illustrated by the orange "R" line in the figure below.
|Typical daily temperature cycle of the surface energy|
budget (Watts/square meter) (Whiteman 2000).
What happens over mountain slopes, however, is strongly dependent on the slope aspect. As illustrated below for north- and south-facing aspects, the amount of radiation intercepted by the Earth's surface varies with season, time of day, and slope angle (the latitude of the Wasatch Mountains roughly splits the difference between the two sites).
|Source: Barry (1992)|
This is why aspect is everything. In the coming days, we'll see a quick melt out on the south-facing aspects, but snow will hang on stubbornly on north-facing aspects.