Meteorologist Britta Merwin

I decided to take a small break from my on going blog series on Why Colorado is so Great and start a new series called The Weather Geek Corner where you can learn about really cool weather phenomena and unlock the true weather geek in you! So lets start with a rare weather event called Thundersnow.

When I was getting my degree I had someone ask me, “Can there be lightning and thunder during a snowstorm?” Well of course many residents of Colorado would most likely say no, but anyone from the Midwest or the Great Lakes might know the answer is YES! Thundersnow is just like a winter thunderstorm. It is an area of convective activity, just like a thunderstorm, that has snow as the primary precipitation instead of rain. So how does thundersnow form?

The main idea is similar to how a thunderstorm forms. There needs to be upward motion to skyrocket air parcels into the atmosphere so they can condense and make convective clouds. The different particles in these clouds can then be separated into areas of positive and negative charge that leads to an electric charge, lightning. So how does upward motion occur? There are three basic mechanisms for the formation of thundersnow:

On the Edge of a Cold Front:
The cold front, advancing dense cold air, pushes under the warmer less dense air pushing it upward causing vertical motion. If this convective cloud forms during winter or in a cold enough air mass a thunderstorm can form with the main precipitation being snow.

On the Backside of an Extra-Tropical Cyclone:
There is strong vertical motion on the northwest side of the “comma-head” of an extra-tropical cyclone. This can give enough vertical motion to create thundersnow.

Lake Effect Snow squalls:
This is the most common creator of thundersnow.

Lets get even further into our meteorology nerd time and talk about how lake-effect snow can lead to a winter thunderstorm. When strong, cold northwest winds rush over the relatively warmer waters of the Great Lakes, bands of snow develop on southern and southwestern lakeshores. Although residents of Buffalo, Syracuse, Erie, and many other cities are used to the seasonal lake-effect snow machine thundersnow is relatively rare. This is partially due to the strict conditions needed for the phenomena to occur. We will use lake-effect snow as our formation example for thundersnow requirements:

Convective Depth of 2.5 to 3 km:
This is the vertical height an air parcel raises before it stops; an ample amount of vertical motion is needed for thundersnow

Limited Winds Shear:
Thundersnow is usually experienced within snow squalls. These are linear snow bands vs. clusters of snowstorms. If there is too much wind shear the linear band is torn apart thus hindering the ideal conditions for thundersnow.

50 km Fetch:
The fetch is the distance in which air travels over a surface. In this case the air needs to travel at least 50 km over the relatively warmer Great Lakes to allow for the air to be sufficantly saturated and gain enough thermal energy.

Storm Top Temperatures of at least –30 Degrees Celsius:
The colder the cloud tops the more reassurance that all the particles are ice rather than supper cooled water droplets. It is thought that the presence of ice crystals leads to the separation of charge that creates lighting and thunder. This is similar to normal thunderstorms as well.

Wow, that is a lot of information. In addition here is something really cool. The snow within winter thunderstorms muffles the sound of the thunder. Thunder associated with regular thunderstorms can be heard miles away, while thunder associated with thundersnow is only heard in a small radius of 2 to 3 km.

To close out this edition of The Weather Geek Corner here are some recorded thundersnow events. Thanks for stopping by!

• Atlanta Metro Area: The Great Blizzard of 1993
• Tri-State Area: The Blizzard of 2006

The phenomenon has also been recorded in the Sea of Japan and Mtn. Everest!