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Weather changes -

After a prolonged El Niño, its contrasting phenomenon—La Niña—finally emerged, though its arrival was delayed and its strength is currently considered weak.

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Late arrival -

Research professor at the University of Miami Emily Becker suggests that the La Niña delay is linked to unusually warm global ocean temperatures, which have persisted for over a year. This prolonged warmth, combined with record-breaking air temperatures in 2024, likely disrupted the typical La Niña development.

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Weaker than expected -

La Niña, marked by strong trade winds and unusually cool Pacific Ocean waters, often brings colder and wetter winters to the northern US. However, this year's La Niña is expected to be weak and may not last long, potentially limiting its impact on US weather.

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Make it rain -

La Niña typically brings increased precipitation to the Midwest. This year, major cities like St. Louis, Indianapolis, and Cincinnati are experiencing one of their wettest winter starts on record, according to the Southeast Regional Climate Center.

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Freezing -

La Niña winters usually bring drier and warmer conditions to the South and Central US. However, since December 2024, brutally cold Arctic air has gripped the eastern two-thirds of the country, and nearly every week since has brought disruptive winter storms.

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Storm with a twist -

These recent storms have brought an unusual twist: thundersnow. This rare phenomenon occurs when a snowstorm is accompanied by thunder and lightning.

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Thundersnow in the US -

On the first weekend of 2025, reports of thundersnow emerged from across the southern Midwest, as well as parts of Maryland, Virginia, and Washington, DC. 

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Thundersnow reports -

On January 5, the National Weather Service (NWS) in St. Louis, Missouri, reported that NASA's GOES-East satellite captured lightning flashes across parts of Arkansas, Kansas, Oklahoma, and Missouri.

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Thundersnow reports -

NWS representatives took to X (formerly Twitter) to announce, "We are getting thundersnow/thundersleet!" They emphasized the intensity of the snowfall/sleet, urging residents to avoid travel whenever possible.

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Warnings -

Winter storm warnings remained in effect for several days across the Central Plains and into the Mid-Atlantic. The NWS warned that disruptive storm conditions were expected to persist until January 6.

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State of emergency -

States of emergency have been declared in Arkansas, Kansas, New Jersey, Missouri, Kentucky, Virginia, and West Virginia, as a powerful winter storm continues to wreak havoc. Overnight, parts of Kansas saw a staggering 18 inches (45.72 centimeters) of snowfall.

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What causes thundersnow? -

Thunderstorms erupt when warm, humid air surges upward, colliding with cooler, drier air aloft. This encounter triggers the formation of towering cumulus clouds.

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What causes thundersnow? -

Inside these clouds, there are light ice crystals that float upwards and heavier ice pellets called graupel that fall downwards. 

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Sparking collision -

When these collide, electrical charges are created, which cause lightning and thunder.

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Positive and negative -

This bumping causes electrons to jump from the ice crystals to the graupel. As a result, the top of the cloud becomes positively charged, while the bottom becomes negatively charged.

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Opposite forces -

This difference in charge between the top and bottom of the cloud creates lightning, according to the National Oceanic and Atmospheric Administration (NOAA).

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Visualizing it -

This builds up a strong negative charge at the cloud base, repelling electrons in the ground below. This is similar to how rubbing a balloon on your hair results in shifting charges, leaving the balloon negatively charged and the hair positively charged.

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Light and sound -

Eventually, the tension becomes too much, and a powerful burst of energy (lightning) is released. This sudden burst of energy superheats the air around it, causing it to explode violently. This explosion creates the loud rumbling sound we call thunder.

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Power combo -

Thundersnow happens when a thunderstorm erupts within a snowstorm.

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Rare phenomenon -

Thundersnow is a rare sight during the winter months. Especially when it's cold enough for snow, the atmosphere is not as energetically charged, and the ground doesn't heat up as much, explains Jon Shonk, a Senior Scientist at the UK's Met Office.

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Where do they occur? -

When they do happen, the Great Lakes region is a common hotspot for thundersnow. Additionally, according to Jesse Ferrell, AccuWeather's senior weather editor and meteorologist, thundersnow is most frequent in the central US and the Intermountain West.

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Lake-effect -

Ferrell explains that intense lake-effect snow bands, characterized by pockets of rapidly rising air caused by the stark temperature difference between the cold air above and the warm lake water, frequently produce thundersnow.

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Seasonal differences -

Surprisingly, these winter factors that suppress thunderstorms actually contribute to their more frequent occurrence during the warmer summer months when the atmosphere is more energized and laden with moisture.

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Why so cold? -

The recent frigid temperatures gripping the US are a result of significant shifts in atmospheric pressure and a disruption of the polar vortex—a swirling band of strong winds that typically confines cold air to the Arctic.

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Thundersnow conditions -

This shift allows frigid Arctic air to plunge far deeper into the US than usual. When this icy blast collides with warmer, tropical air masses from the south, the clash can create the unique conditions needed for thundersnow.

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Is thundersnow dangerous? -

Josh Weiss, a forecaster at NOAA's Weather Prediction Center, warns that "Like any storm that produces lightning, thundersnow can be dangerous." However, the lightning and thunder associated with snowstorms is typically less frequent and less intense than the powerful displays we see during summer thunderstorms.

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Not loud enough -

Unlike the booming thunder that can be heard from miles during summer storms, snow tends to dampen the sound, making it difficult to hear from a distance. 

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Not loud enough -

This muffled thunder can lull people into a false sense of security, making them less aware of the approaching storm and potentially increasing their risk of being struck by lightning.

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Main danger -

Experts emphasize that the most significant danger of thundersnow is the heavy snowfall itself. "Thundersnow usually occurs only during the most intense snowfall," Weiss said, which can drastically reduce visibility and create treacherous travel conditions.

Sources: (Live Science) (CNN)

See also: Key climate events to watch out for in 2025

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