For our first installment of "Norm Knows"...Chief down at Bowling Green State University asked: "How do you get thunder and lightning with a blizzard?".
The short and simple way to answer would be to say the same way you get thunder and lightning in any storm. But in reality, it's much more complicated than that.
Before we can make a lightning strike, we have to alter the electrical charge within the cloud. This happens as air rapidly rises up into it. This section of the storm is commonly known as the "updraft"...and the overall "upward motion" is known as "convection".
As we get up above the freezing level inside a storm, even in the depths of summer, suspended particles of ice or even liquid drops, (liquid water droplets in a sub-freezing environment are known as being "supercooled"), collide into one another. As they do, they can form a slushy, soft ice-water pellet known as groupel.
As the collision takes place...some of the electrical charges are re-arranged. The ice crystals are thought to retain the positive charge...while the groupel is though to take on a more negative charge.
The ice crystals are then carried further up into the storm by the updraft...while the heavier pieces of groupel get pulled downward to the middle and bottom portions of the storm by gravity.
It doesn't take long for the top of the cloud to become mostly positive...while the bottom portion becomes more negative.
Once that "charge separation" gets big enough, the difference will be equalized by a spark we see and know as a lightning bolt.
That bolt can travel within the cloud, from cloud to cloud...or from cloud to ground.
Once that charge is equalized...other areas can continue to follow suit and repeat the cycle over and over again, as long as the updraft keeps those particles on a collision path.
With that explained...we can now focus on "thundersnow".
The entire process is, roughly, the same...except now we have temperatures down at the surface below freezing as well. Cold enough to produce snow instead of rain.
The bigger area of unstable air is now aloft...well up above the surface where we all walk around. When the upward motion of the storm is concentrated well up above the ground we refer to the convection as being "elevated".
Strong winter storms that produce a lot of upward vertical velocity (UVV) will cause the same types of collisions to occur. The charge separation is built up...and BOOM! A lightning strike in the middle of a snowstorm!
Thundersnow is rare because the UVV is rarely strong enough in winter storms to create enough collisions in an updraft. The lifting within winter storms is normally very gentle when compared to that of a thunderstorm.
Only the most intense of winter storms, most commonly those that reach blizzard criteria, will be able to produce lightning and thunder. And to get the right circumstances of lift, moisture and surface temperature all coming together for lightning when it's cold enough for snow is rare indeed.
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