At 4:30 this morning, after a manic tug-of-war between our English Cream Golden Retriever and me, a flash lit the sky, followed by a low rumble while heavy snow poured down from the heavens above.
At first, I thought the flash was from a hand slipping on the sheet and smacking me in the head—it wouldn’t be my first time—but the jolting sound brought me out of my stupor. Thunder during a snowstorm always carries a shock because it rarely happens. The moment brought back another memory from long ago.
In January 1976, during a brutal Wisconsin blizzard, a sharp crack of thunder rolled through the house and the falling snow, making the fine china in my parents’ dining room shake. I was 9 years old, and decades later, I still count every time I’ve heard that sound on one hand.
Not to mention fighting AC/DC lyrics each time I say the word “thundersnow.”
Meteorologists call the event thundersnow, which forms when the same ingredients that drive summer thunderstorms are inside a winter storm: moist hot air rises rapidly through colder air. That rising motion builds electric charge inside clouds packed with ice crystals and snow, while lightning flashes and thunder follows even though snow falls instead of rain.
Thunderstorms occur when warm, moist air rises and condenses in cooler, drier air above it, forming towering cumulus clouds. Inside these clouds is a combination of light ice crystals, which float upward, and soft hail known as graupel, which is denser and falls downward. This causes both particles to collide, transferring electrons from the ice crystals to the graupel. The result is a cumulus cloud with positively charged ice crystals at the top and negatively charged graupel at the bottom, according to the National Oceanic and Atmospheric Administration (NOAA).
This builds a negative charge at the base of the cloud, repelling electrons in the Earth beneath it. The charge difference between the cloud and the ground builds up until eventually the potential energy is discharged as a bolt of lightning.
The energy from this strike heats the surrounding air, causing it to expand outward and producing the rumbling sound we know as thunder.
Thundersnow occurs when this weather system develops amid a snowstorm.
The combination requires strong upward motion in the atmosphere, a strong moisture supply, and sufficient instability for clouds to grow vertically. Winter storms rarely produce that mix, which explains why thunder in a snowstorm surprises even experienced weather observers.
The rarity stands out in the research, where studies of storms show that thundersnow occurs only about 7 times out of every 100,000 heavy snowstorms. That heavy snowstorm muffles sound, meaning thunder often goes unheard unless lightning strikes within two or three miles. Those factors combine to make the event feel almost mythical to people who experience it.
Patrick Market serves as director of the School of Natural Resources and Professor of Atmospheric Science at the University of Missouri. His research into thundersnow has tracked dozens of storms across North America, highlighting the phenomenon that usually marks intense snowfall. In about 86% of observed cases, the storm dropped more than six inches of snow in a single day, while lightning often forms in the same narrow bands where snow piles up fastest.
Though thunder and lightning in a snowstorm are predictors of heavy snowfall, researchers have recently learned that heavy snowfall is not a predictor of thunder and lightning, and are still uncovering why.
Until the last 20 years, researchers couldn’t even reliably identify thundersnow, let alone study its inner workings. With new technology monitoring weather from space, we’re learning more about thundersnow than ever. This research will have real-life impacts on public safety, from creating warning systems to even changing guidance for when to fly planes and launch rockets.
The electrical process deep inside those storm clouds resembles a summer thunderstorm: ice crystals collide with heavier particles called graupel, a soft form of hail. Those collisions transfer electrical charge between the particles.
Positive charges ride upward in the storm, while negative charges gather lower in the cloud. When the electric field grows strong enough, lightning discharges and thunder rolls across the snow-covered landscape.
Thundersnow also warns forecasters about dangerous snowfall rates. When lightning strikes during a winter storm, snow can fall at 2 to 4 inches per hour, severely limiting visibility and creating road hazards in a heartbeat. Meteorologists closely monitor radar and lightning detection networks when those signals appear, as they highlight the most intense part of the storm.
That rare flash and rumble early this morning carried the same message the storm delivered decades ago during a blizzard in 1976. There are times when winter hides enormous energy inside thick gray clouds. Most storms quietly pass, but on the rare chance when lightning tears through falling snow, the atmosphere briefly reveals just how powerful a winter system can become.
And, best of all, the thunder crack startled Mabel, so I had the upper hand with the comforter.
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