We know we’re in for a sizable snow storm, but just how does snow accumulate?
Find out with the latest Science Behind the Forecast.
This transcript was edited for clarity and length.
Bill Burton: It's time for us to take a look at the Science Behind the Forecast as I'm joined by WAVE 3 meteorologist Tawana Andrew. Good morning, Tawana.
Tawana Andrew: Good morning. Today's topic, of course, is winter related.
BB: There's just a little bit of ugliness headed our way, and that's our topic today, snow, and specifically snow accumulation. What do we need to know?
TA: There's several things that can impact how snow accumulates. First, where the snow is falling. Let's say we have an area with a bunch of grass, or any other kind of vegetation. That, technically, is a lot more exposed to the cold air, because there tends to be a little bit more of those air pockets in between grass and in between leaves. That allows for temperatures to drop more easily in that vegetation. That's why the snow will accumulate there more. But on our roads, it's a different situation. Because they're connected to the Earth's surface, that allows them to be warmed by the ground below. And it does take time for our soil temperatures to adjust to colder air, so there will be a lag time between the air temperature dropping and the ground temperature dropping. Since roadways are absolutely fantastic at absorbing not just solar radiation, but terrestrial radiation that allows them to warm up faster, but also cool down more slowly. Now, in the cases of bridges and overpasses, we always hear, they will freeze before roadways
BB: That's what I’ve always been told.
TA: That is true, because you have the air above and below these overpasses or bridges, and that allows their temperatures to drop faster compared to the roadways that are connected to the ground. But if the wind is strong, the flat surface of a roadway can actually help to limit snow accumulations as well, because that just gives something easy for the wind to blow all of that snow off of. But vegetation traps things a little bit more and limits how much that wind can impact the snow as it starts to pile up, as it remains a little bit more sheltered.
What happens before a winter storm can also affect accumulation. Let's say we have a bunch of days before a winter storm moves in and temperatures are well above the freezing mark. That limits how much the snow can accumulate initially. Maybe not on the long run, but initially, as that snow moves in and starts to accumulate, those warm ground temperatures can influence that because in physics, or just in life in general, heat energy tends to move from warmer to colder things, so that heat will be conducted from the ground into the air, helping to melt a significant amount of the precipitation that will fall. Especially on concrete and asphalt services. That's why you don't tend to see everything sticking at first when you have a warmer day prior to a winter storm moving in.
But on the other side of things, if you have several days of sub freezing temperatures before a winter system that will limit any melting at all, because that ground will allow any type of precipitation to basically stick. It's like putting your tongue on a frozen pole. It's gonna stick.
BB: Just to be clear, don’t do that!
TA: Yes, don't do that!
That can cause even more issues when it comes to travel. Because then it's kind of harder to get the snow, the ice, whatever it is, off the ground, and get everything moving again.
