'Thundersnow' is heading to the UK - but what actually is it?

Daily Express readers: get excited, because your dreams could finally be about to come true - some seriously fun weather in the form of ‘thundersnow’ is on its way to the UK.

Yes, we know what you’re thinking: “This is just the latest in a load of nonsense made-up terms like ‘weatherbomb’ and ‘winterblast’ and ‘snowmortar’ (we just made that last one up) and it’s just a load of nonsense designed to make weather sound more exciting than it is in order to put something on the front page of the Express alongside the Diana and Maddie stories.”

Well no, for once, thundersnow is a real thing. Here’s what’s going on.

What is thundersnow?

Thundersnow is, as you might expect, a combination of two of the best bits of weather: thunder and snow. It’s a thunderstorm where, instead of it raining, it snows instead.

Why is it interesting?

Well, it’s a relatively rare phenomenon. Thunderstorms are much more common in summer months, but can form in wintry conditions.

Eleanor Bell, principal meteorologist of The Weather Channel, says: “There needs to be an upward motion for the thunder to develop, warmer air trying to rise under colder air. It is less common than normal thunderstorms because it occurs in the colder months of the year when the air close to the ground is cold enough to produce snow.”

Read more: The world’s weirdest weather phenomenon

What causes thundersnow?

There are usually three causes of thundersnow:

1. A normal thunderstorm on the leading edge of a cold front or warm front that can either form in a winter environment, or that runs into cool air, and where the precipitation takes the form of snow.

2. A heavy synoptic [large scale] snowstorm that sustains strong vertical mixing which allows for favourable conditions for lightning and thunder to occur.

3. A lake effect or ocean effect thunderstorm which is produced by cold air passing over relatively warm water.

Does it have any unusual features?

Yes - a unique aspect of thundersnow is that the snow acts as an acoustic suppressor of the sound of thunder. In a normal thunderstorm, the sound of thunder can be heard many miles away, while in a thundersnow event, you’ll only hear it if you’re within two to three miles of the lightning source.

However, for those disappointed that they might miss out on the action, don’t despair, because another feature of thundersnow is that the lightning will seem brighter - because it reflects off the snowflakes.

Where and when does it normally occur?

Thundersnow is normally associated with the Great Lakes area of the United States and Canada, the midwestern United States and the Great Salt Lake, as well as Halifax, Nova Scotia and Bozeman, Montana. It is also common around Kanazawa and the Sea of Japan, the elevated provinces of Israel and Jordan and even around Mount Everest. 

In the US, March is peak thundersnow month, however, on average, only 6.4 events are reported in the country per year.

The UK and other parts of northwestern Europe occasionally report thunder and lightning during sleet or snow showers during winter and spring, but the phenomenon is rare.

Is it dangerous?

Thundersnow produces heavy snowfall - between 5-10cm per hour, meaning that visibility is severely limited. However, as thundersnow is often part of a severe winter storm or blizzard, this can exacerbate the effect, with visibilities in thundersnow often under 400m.

The associated winds can create extreme wind chills and may result in frostbite. However, unless you’re planning on going to somewhere seriously remote, we’d imagine you’d be alright.

(Image: Craig Whitehead/Rex)