2.1.9 Solar variation

Length of day progressing throughout year at latitude 45 ° NAt latitudes where snowpack is typically found, the amount of solar energy varies significantly throughout the year.

Although the smallest amount of solar energy reaches the Earth's surface in the Northern Hemisphere in late December, snowpack depths peak during late winter/early spring. This is due to two main factors.

  • Snowpack is cumulative, typically deepening throughout the cold season
  • Snowpack depth does not decrease significantly until melting offsets replenishment by new snowfall. In areas north of the Equator, daytime lengths increase most rapidly during the late March period—the point at which days become longer than nights. On average, this is when daytime melting exceeds new snow accumulation.

You might think that the coldest temperatures of the year would correlate with the shortest days. But that's not typically the case. The coldest ground and atmospheric temperatures of the year typically lag behind the winter solstice (December 21 in the Northern Hemisphere) when the minimum solar energy reaches the Earth's surface. That's because the thermal energy stored in the ground from the previous summer and fall delays the coldest temperatures until after the winter solstice.