Even though we got some snow yesterday, about a half an inch to an inch in most areas, I was asked the question again. It’s a question that I’ve been asked a thousand times before. The question was e-mailed around 5 AM yesterday morning BEFORE the rain changed to snow. What’s the question you ask? Why does it seem that Memphis always misses the the snow?
Here’s the e-mail I received:
I NEED ANSWERS!!! You can give it to me straight…just need to know:
WHY DOES THIS ALWAYS HAPPEN?
Is it the “Bluff Effect”?
Is it the “Heat from the City Effect”?
Is it the Mayor??
Is it “Dave Brown hates snow and has a LOT more power than we all thought?”
Is it a fluke?? (Which doesn’t seem logical since it happens so often)
Why does the stuff LITERALLY go around, above, below…everywhere but here…
I can’t take the disappointment anymore….really….
Well, here’s the answer:
It’s a matter of geographical location and thermodynamics. Three things are required for snow; moisture, lift, and cold air in all levels of the atmosphere. Due to our geographical position it is often difficult for us to have all three of these elements in place at the same time especially when it comes to temperature. As was the case overnight Tuesday, we had moisture and lift but the temperature element was not there. Yes, it was cold at the surface but the temperature was warmer with height. Due to our southern geographical location warm air is typically in close proximity during the winter months. This warm air will provide moisture but it will also override a cold air-mass and cause the warming of middle layers of the atmosphere to rise above freezing. In order for an ice crystal in the upper levels of the atmosphere to reach the ground it must have temperatures at or below freezing from its point of origination to the surface. If it falls through a layer of air that is above freezing and more than 1500 ft in depth that ice crystal will melt completely. If the layer is less than 1500 ft thick the crystal will not melt completely but will instead melt to some degree and combine with other slightly melted crystals to form an ice pellet. Or if it does melt completly then it must fall through another layer of air that is below freezing and at least 1500 ft thick for it to refreeze but it will not be an ice crystal it will instead be an ice pellet since it would be a frozen raindrop, we refer to this as sleet. Now if the temperature is at or below freezing at the surface but the layer of air is not at least 1500 ft then the melted ice crystal or raindrop will reach the surface in liquid form but will freeze on contact with the frozen surface, thus freezing rain.
It is also important to keep in mind that cold air is heavier, more dense, and holds less moisture than warm air. A strong cold air-mass that moves in from the north will be drier and since it is more dense it will suppress the ability for air to rise or lift and it will force the warm moisture rich air-mass south so, that by the time it arrives here we get the cold temperatures and maybe enough moisture to produce clouds. So, with limited moisture and little if any lift we don’t get snow we just get cloudy and cold. On the other hand if there is plenty of moisture and lift but a layer of warm air near the surface then we get a cold rain instead. By the way, all of those elements finally came together for a brief period shortly after 5 AM Tuesday morning and we did indeed get some snow.
Snow is not common in the Mid-South during the winter months but it’s certainly not rare. It’s not a fluke, don’t blame the bluffs, the mayor, or the weatherman (Dave Brown really does like snow, just not a lot of it.) As you can see it is a very fine balance of elements that must be in place for snow to fall in the Mid-South. It’s the law of thermodynamics and our geographical position that are to blame.