Snow melt accelerates with a perfect storm of conditions

Weather Blog

ROCHESTER, NY (WROC) – After weeks of below freezing temperatures, Rochester racked up a 16″ snow depth. Deepest since March 2017, this snow depth is great for outdoor winter sports. The only problem is the forecast. Major melting will happen over the next week as afternoon highs climb into the 40s. There are four main factors to take into account when talking snow melt.

Temperature

This one may seem obvious, but the number is important. If your temperature is above freezing, melting will occur. Generally speaking the warmer it is, the more melting that will occur. There are plenty of caveats outlined below.

Sun Angle

Sun angle and cloud cover also play a role. If the sun is out and we are further in winter or early spring, a higher sun angle (higher in the sky) will be able to transfer energy to the snowpack and melt snow, even if temperatures are below freezing. For example, it can be in the middle 20s with sunny skies in early March and a snow pack can shrink.

Remember that temperature you see reported on TV or on your phone is taken around two meters above the ground. The very thin layer of air directly above the snow will always be at or below freezing.

If the snow pack is older, there will likely be a lower albedo, so it will absorb more heat energy. A fresh snowback is generally lighter and has a higher albedo.

Wind

Wind plays a very important role in snow melt. If you understand how the wind chill works, then you can make sense of how a stronger wind can help erode a snow pack. When temperatures are above freezing, remember that the snow is at 32°F. If no wind is present, then a layer of insulating air will help prevent from rapid melting. If there is wind, the insulated layer is “blown away” and warmer air is allowed to mix down onto the snow pack. That puts warmer air along the surface of the snow. This accelerates melting.

A 38° day with wind can melt snow just as fast as a 45° day that is calm.

Rain

Without getting too deep into the science of how rain can impact a snowpack, here are two scenarios. A day of 50° with rain versus a day of 35° with rain. With the first scenario, a warm rain droplet will cut through a snowpack and may even make it to the surface. Some of the energy will be transferred to the snowpack and some to the ground. In the second scenario, not only does the raindrop transfer energy to the snowpack, but it freezes within the snowpack and releases latent heat. That helps warm the snowpack even more and melting will be even more effective under this scenario.

All these factors are important and can all play a role with some being more important than others. Each can play off each other and have different impacts on how the snow pack melts. Here is a list of other factors that may contribute:

  • Type of snowpack
  • Water content of snowpack
  • Heat transfer from the ground below
  • Time of day
  • Elevation of snowpack

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