Why leftover snow can often lead to cooler temperatures than models forecast
After the brutal cold this weekend, areas across Central Missouri are finally starting to experience at least some relief. Even though this relief is taking over, it won't last long, and there may be additional factors that could push the forecast toward a more frigid outcome than some models suggest. The main culprit will be the leftover snow accumulation observed across the state.
Albedo is the function of this extra factor playing into the forecast throughout the next couple of days. Albedo is defined as the measure of how reflective a surface is, and it is put on a scale from 0 to 1. Less reflective surfaces will have a value closer to zero, while more reflective surfaces will have a value closer to 1. This means lighter surfaces, like snow, will have a higher albedo and therefore be more reflective. Darker surfaces, like asphalt, will have a much lower albedo, and the result will be a less reflective surface.
Take the more typical example where darker surfaces, like asphalt, are not covered in snow. As the sun emits solar radiation into the Earth's atmosphere, it hits these surfaces that have a low albedo and are less reflective. This lower reflectivity leads to a lower amount of radiation being "bounced" back into the atmosphere and more radiation being absorbed by the surface the solar radiation is hitting. This absorption causes the surfaces to emit more of their own type of radiation, which causes the surface to be warmer and also leads to a more efficient warming of the air surrounding it.
In the situation that is currently in place today, most darker surfaces are covered in the much lighter snow with an albedo close to 1, which is significantly more efficient at reflecting incoming solar radiation. So, instead of these surfaces absorbing most of the incoming solar radiation, the majority of it is "bounced" back into the atmosphere. Since less radiation is absorbed by these snow-covered surfaces, they in turn emit a lower amount of their own radiation. This causes the surface to be cooler than the typical scenario, which then means it is less efficient at warming the air surrounding it. This is the first reason why temperatures may be cooler than what models may be predicting over the next couple of days.
The second reason is because of a concept called evaporative cooling. Although temperatures will not be above freezing for the next couple of days, the incoming solar radiation on sunny days is still more than enough to melt the snow that is in place. If the air is dry enough, it can also heat that snow melt to the point of evaporation. This is because drier air has the potential to hold significantly more moisture compared to an already near-saturated atmosphere, where the moisture it can hold has already almost been maxed out. This evaporative process requires a large amount of atmospheric energy, so this means that there is not nearly as much energy available that would go into heating the Earth. This results in a cooling of the surrounding air and a colder forecast overall.
