That is not a very simple question to answer because there are several atmospheric factors that help determine how fast snow and ice will melt. These factors are constantly changing and in a “tug and pull” of helping and hurting the melting process.
The most obvious is temperature. If the air temperature is above 32°F snow and ice will start to melt, at or below 32° and it will remain frozen. Think about a popsicle… inside the freezer it stays frozen, outside it starts to melt.
The amount of sunshine plays a big factor. On a sunny day, the energy from the sun warms the surfaces near, on, and under the snow and ice. If the surface temperatures warm above 32°, the snow and ice touching the surface will warm and begin to melt. This is why we can get melting snow on days when the air temperature is still below freezing.
Rainfall can also be helpful. Rain is obviously liquid and therefore above freezing. As the above 32° rain drops fall on the below 32° snow and ice heat will transfer and in most cases result in more melting.
Melting is only part of the story… Yes, we want the snow and ice to melt but we also want to avoid the refreezing of the leftover puddles. In order to do that, we need evaporation. That is why the dew point (amount of moisture in the air) and wind are also helpful to remove snow and ice. If the air around the snow and ice is dry (low dew point) it can “hold more” of the moisture as it evaporates. A light wind also helps because it keeps the air mixed, allowing dry air to mix back in and more evaporation to occur.
So in a perfect scenario, the day after a snow storm would be warm, sunny, with a quick rain shower mixed in, low dew point, and light winds. Unfortunately, that situation almost never happens. So… when will it melt? That all depends on how many good versus bad melting factors we have and for how long.
-Meteorologist Myles Henderson
