Weather 101: This week we will discuss the different types of winter precipitation we receive here in the Capital Region and how it is that we can see all these different types in just one storm.
You have to envision the atmosphere in 3 dimensions. Typically as you go up in height the temperature will decrease. So, at the cloud level it is always cold enough to support frozen precipitation, however, just because it is cold enough up there does not mean we will see all snow at the surface.
Lets talk about just plain old rain. There is a shallow layer of cold air up in the clouds, however, as the precipitation falls it will encounter a very deep layer of warmer, above freezing air. This will melt the frozen precipitation and we will only see rain. Now, if temperatures are borderline and the precipitation is falling rather heavily, the snow can overcome this warm layer and you may see mainly rain with a few flakes mixed in.
Another precipitation type that we will typically see in the winter and early spring months is freezing rain. Similarly to the plain rain, precipitation begins as snow in the clouds, it will then encounter a layer of above freezing air which will allow that snow to melt to rain. However, the difference is that when it gets closer to the surface temperatures are at or below freezing. This layer of below freezing air is rather shallow and is not deep enough to refreeze the rain and thus the rain will then freeze on contact to any surface.
Sleet is formed very similarly to freezing rain. As the snow falls through the atmosphere it will encounter a layer of above freezing air. However, in this instance this layer is rather shallow. The layer of below freezing air at the surface is deep enough to refreeze that melted precipitation and change it to what we call sleet. These are little ice pellets, sometimes mistaken for hail, however, hail will not form outside of a thunderstorm. So typically you would only see hail in the summer months.
Just plain old snow is the easy one. The layer at the cloud base is of course below freezing, that layer of below freezing air extends all the way to the surface so there in no melting occurring and this is when we will see just plain old snow.
A lot of this has to do with the position or tracks of storm systems. If you want all snow, the best track of a winter storm would be south and east of the Capital Region. The reason being that when the storm tracks in this fashion it is able to draw in cooler air from the north and west… Winds flow counter clockwise and inwards around areas of low pressure, so if the storm tracks west of the Capital region it would typically promote a warmer flow of air from the south and we would ultimately end up with just rain with perhaps some snow on the tail end of the system.
Sometimes, even with a more favorable snow track winds can shift to the east and bring in slightly milder air aloft off from the Atlantic ocean, this is when we will typically see a mix of rain sleet and snow. That mix is usually observed south and east of Albany in this particular setup.
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