Why some snow piles across Central Missouri haven’t melted yet
It has been over two weeks since Central Missouri's first widespread snowstorm, which brought measurable snow across the state. Since then, it has stayed largely dry and has also gotten noticeably warmer, with temperatures breaking the 50 and 60 degree mark over the past couple of days. With temperatures getting almost 30 degrees above freezing each afternoon, and with the amount of time it has been since our last snowfall, you would think that any lingering snow would have been gone by now. But if you have been outdoors, you know that this isn't the case. Although snow accumulations are practically gone, the large piles from snow plows remain, and there are a couple of reasons why.
The first main reason is the albedo of the snow. Albedo is a measure of how reflective a surface is, with higher numbers meaning a higher reflectivity. Snow is one of the most reflective surfaces on Earth, so instead of absorbing incoming solar radiation, it reflects it into the atmosphere. This lack of absorption leads to the snow pile not receiving an efficient heating mechanism compared to the darker surrounding surfaces that are absorbing this radiation and, in turn, emitting more of their own form of radiation.
The second reason is that even though air temperatures have been well above freezing the past couple of days, the ice and snow aren't able to immediately turn into water when temperatures reach above the freezing mark. This transition from a solid to a liquid requires a large burst of energy just to break the crystal bonds. This transition is called latent heat, and once the snow pile reaches the temperature at which it transitions from a solid to a liquid, it must first absorb a certain amount of energy from the atmosphere before the temperature in that mass can change any further. This is a very large amount of energy, and during this time of the year, it is often hard to achieve, so the majority of the snow piles often remain.
Finally, these snow piles act like blankets, trapping the cold on the soil it is sitting on. This leads to the temperatures on the surfaces that are consistently staying below freezing since they themselves can't receive any incoming solar radiation to absorb. Most soil temperatures across the state are currently just above or around freezing, so any surfaces still covered by snow have no way of getting above that mark. So, not only is it hard to melt these snow piles from the top, but it is also extremely hard to observe any sort of melting at the bottom of the piles.
The process of melting these snow piles is a bit more complicated than just achieving temperatures that are well above freezing. It takes something like rain (warmer water), wind, or time to accelerate the process of snow piles fully melting away. Looking at the forecast, there will be opportunities like continued temperatures above freezing and chances for rain that will aid in shrinking any snow piles that remain.
