Freezing Weather and Thundersnow

January 29, 2016
National Interagency Fire Center

The only thing more spectacular than a cold spell bringing freezing temperatures to all 50 states is a cold spell that brings widespread freezes and (Boom! Sizzle!) THUNDERSNOW.

That’s what we saw this November, a massive freeze and the rare phenomenon of thundersnow.

A November surprise. Brrr! Credit: NOAA

On November 17 a massive cold spell brought freezing weather to 49 states. Only Hawaii wasn’t engulfed by the cold and even that sunny state had 31°F weather on the top of Mt. Kea. The massive freeze lingered for days. As noted in my last blog, the abnormally cold polar air mass is suspended just north of us and like the sword of Damocles, it takes very little to encourage it to fall south.

This year, however, the cold is bringing not just cold, misery and snow, but also rare thundersnows—thunderstorms that produce snow instead of rain. High winds, as strong as a tropical storm whip the land. Even worse, this weather event typically brings an additional six inches of snow. Then, when everything melts, a high risk of floods.

Thundersnow or “white lightening” Source: National Interagency Fire Center

Fortunately these types of storms are as rare as they are spectacular, but what causes them? The answer is almost absurda hot air sandwich.

In a normal thunderstorm, an updraft of hot surface air streams into the colder air overhead. The moisture in the warm air freezes into ice and sleet, which is heavy enough to fall. When it drops into the warmer air below, it melts back into water and rains. Sometimes, however, the updraft catches it. The clouds become very turbulent, filled with ice, slush and droplets swirling up and down. They bump into each other, creating a static charge. (It is rather like the charge that builds up when you drag your feet on a rug,) The charges accumulate and finally spark into lightning with a thunderous crackle.

Thundersnows are created by hot air sandwiches. The warmer air from the Great Lakes is lifted over the colder, heavier air around their shores. When the rain falls, it enters the cold air and refreezes into snow. Meanwhile, the storm overhear roars on.

This type of weather is not only spectacular, it is rare.

If any of you have been in a thundersnow, what was it like? Share it here, you are among weather-lovers.

About This Blog

Are you a weather watcher? Welcome to “Weather Whispers” by James Garriss and until recently, Evelyn Browning Garriss. With expertise and humor, this column covers everything weather—from weather forecasts to WHY extreme weather happens to ways that weather affects your life from farming to your grocery bill. Enjoy weather facts, folklore, and fun!

With heavy hearts, we share the news that historical climatologist and immensely entertaining Almanac contributor Evelyn Browning Garriss passed away in late June 2017. Evelyn shared her lifetime of weather knowledge with Almanac editors and readers, explaining weather phenomena in conversation and expounding on topics in articles for the print edition of The Old Farmer’s Almanac as well as in these articles. We were honored to know and work with her as her time allowed, which is to say when she was not giving lectures to, writing articles for, and consulting with scientists, academia, investors, and government agencies around the world. She will be greatly missed by the Almanac staff and readers.