A very cold atmosphere will contain little water, and so it will snow quickly. In a very arid climate, such as the (antic) Arctic, temperatures are so low that there is little evaporation of water from the ground or water and therefore little moisture is produced. But for snow to form, there must be moisture in the atmosphere, and very cold air contains very little moisture.
Snow falls at temperatures that meet or fall below the freezing point of water. This means 32 degrees Fahrenheit. However, most atmospheric water is impure and freezes at temperatures lower than this. The temperature needed for snow to remain on teh ground decreases with rising elevations.
At very low temperatures, such as -40 degrees Fahrenheit and Celsius (the point where the temperature scales are the same), there is so little moisture in the air that snow formation becomes extremely unlikely. However, even colder air can hold some moisture, so there is no theoretical point below which it gets too cold for snow, but the colder the air, the less likely it is for ice crystals to precipitate and turn into flakes that fall to the ground in the form of snow.
Snow from Experience
Snow can still fall all the way to the ground even if the surface temperature is above freezing. The last “fun fact” (so to speak) is that once the snow starts, the temperature actually drops by a few degrees due to evaporation. Once the temperature rises above freezing, the falling snow begins to melt, but as the melting process begins, the air around the snowflakes cools.
Snow forms when the air temperature is zero or below (0 degrees Celsius or 32 degrees Fahrenheit) and there is very little moisture in the air. Even in the coldest place on Earth, Antarctica, it snows at temperatures well below freezing. Usually, in the atmosphere where snow forms, it is a few degrees below the ground.
Even if the temperature does not reach 32 degrees, the sun can still warm the ground, snow, mud, houses, etc. When this happens, the snow or ice will still melt even if the temperature doesn’t hit freezing. If the temperature is above 32 degrees Fahrenheit, the snow and ice will begin to melt.
The Conditions for Snow Formation
Snow forms whenever there is enough moisture in the atmosphere and the temperature is at or below freezing. Snow forms when temperatures are low and moisture in the form of tiny ice crystals is present in the atmosphere. Snow is formed from water droplets in the air that form ice crystals when atmospheric temperatures reach or fall below freezing. Snow crystals form when tiny supercooled cloud droplets (about 10 mm in diameter) freeze.
Therefore, clouds that form at lower temperatures, if they ever form, contain much less suspended water in the form of ice crystals, the original sites for the formation of snow crystals.
Snowflakes retain their brittleness and fall like snow if the air temperature is below the freezing point of the clouds on the ground. Generally speaking, the colder the weather, the easier it is for snowflakes to form. If there is enough water, the flakes may get larger and snow may occur.
If the temperature is above 2°C, the snowflake will melt and fall instead of snow in the form of sleet, and if it is even warmer, it will rain. At temperatures above 2 degrees, the snow will fall in the form of sleet, and at temperatures above 5 degrees – in the form of rain. Up to about 1 °C above the no-melt line it mostly snows, and from about 1 °C to 2 °C above the line it mostly rains but snow is possible.
However, if snow falls to the ground when the surface temperature reading is 40 C (or higher), the snow will begin to melt almost immediately after impact.
The Temperature for Snow to Remain on the Ground
For snow to fall and hold, the temperature of the ground must be below two degrees. The best chance to see 50 F temperatures and snow is when the air is dry and the snow is heavy. Temperatures will drop quickly and snow may turn into rain. If you’re wondering at what temperature snow should fall, the answer is 32 degrees Fahrenheit.
However, this is not the main explanation for why it can snow when temperatures are above freezing. The figure below shows that there is a clear dependence on humidity: the drier, the hotter it can be during a snowfall. However, technically it is not temperature that prevents snow from falling, but rather the complex relationship between temperature, humidity and cloud formation. Many people think that snow should be below zero (0°C), but in reality the temperature of the ground should fall below 2°C.
However, in some areas, an increase in the thickness of the snow cover may be observed due to higher temperatures for latitudes north of 40 degrees. A warm front can produce snow for a period of time as warm, moist air takes precedence over sub-zero air and creates precipitation at the boundary.
What Happens in Clouds for Snow Formation
Snow is formed from water, so water vapor in the air is needed to form snow. When the melt water reaches the frozen air, the ice builds up to form a dam, and the snow that later melts cannot drain properly through the dam. Roof ice dams form when snow that has accumulated on a pitched roof melts and runs down the roof under an insulating snow cover until the air temperature drops below freezing, usually in a gutter.
Snow is made up of individual ice crystals that grow in suspension in the atmosphere, usually in clouds, and then fall to accumulate on the ground, where they undergo further changes. The physics of snow crystal formation in clouds depends on a complex set of variables, including humidity and temperature.
They usually form when there is moisture in the atmosphere, but at temperatures slightly above freezing (zero degrees), they melt at the edges, attaching themselves to other crystals, forming larger snowflakes. If so, the staple will obviously melt. If the temperature is above zero, there are no parameters by which the type of precipitation can be determined with certainty.
Predicting Snowfall
So all we can predict is the likelihood that snow will actually fall. This can be done using the results of Haggmark and Ivarsson (1997), corrected only for the use of frozen-bulb temperature and not wet-bulb temperature.
The bottom line is that there is a calculator with which you can estimate the likelihood of snow. Initial snowmelt models used the degree-day method, which emphasized the temperature difference between air and snowpack to calculate snow water equivalent, SWE.
Scientists are still working to better understand the harsh winter climate, as changes in weather patterns and even the smallest fluctuations in temperature can actually determine whether winter precipitation will fall in the form of snow, sleet, freezing rain, or even regular rain. However, the truth is that many things have to happen for snow to form in the atmosphere. Here’s everything you want to know about the temperature at which snow falls… and melts.
An observer sees light returning from nearby surface layers (mm to cm) after it has been scattered or reflected from other snowflakes only a few times, and still appears white.