Probing Question: Why doesn't it thunderstorm in the winter?

Mar 29, 2007 By Meghan Holohan

Some parents tell their children that thunderstorms occur when God goes bowling, but an observant youngster might wonder why The Big Guy only bowls in the summertime.

The short answer? "In the summer there's a lot more moisture in the air," said Yvette Richardson, assistant professor of meteorology at Penn State.

"Any thunderstorm requires moisture, instability and some mechanism for lifting, such as a front," Richardson continued. "It is harder to get all of these to come together in the winter."

Thunderstorms literally begin at the ground level: The sun's rays are absorbed by the Earth, which warms the air above it. As these updrafts of heated air rise, they carry along water vapor, which -- as the warm air ascends and cools -- condenses into liquid, releasing latent heat.

This heat further warms the air, ultimately creating low hanging cumulus clouds -- the clouds that resemble fluffy cotton balls. Explained Richardson, "The warmed air in the cloud is less dense than the surrounding air, making it buoyant."

This buoyant air rises quickly, starting the formation of the thunderstorm. As the cumulus cloud grows higher and bigger, the moist air inside of it accelerates upward until it reaches a level where it is colder than the surrounding air. Heavy droplets of water and ice particles darken the cloud and spread out horizontally to transform the fluffy cumulus shape into a cumulonimbus -- or "anvil-cloud," so named for its typical shape, flattened at its top with a heavy base.

Most importantly, hailstones and ice particles collide with each other, transferring charge in the process. The hailstones fall to the lower portion of the cloud, giving it a negative charge. The ice crystals rise upward, carrying a positive electric charge to the cloud's upper end. This "charge separation" grows more intense with each collision inside the cloud -- so intense, in fact, that the negative charge at the cloud's lower end actually repels electrons at the Earth's surface deeper into the planet. Consequently, the ground becomes positively charged and the electric field cuts a conductive path between the cloud and the Earth. The result? A high voltage surge of electrons, otherwise known as lightning.

The accompanying boom, called thunder, comes from sound waves created when the air is heated suddenly by the lightning and then cools rapidly.

Typically, after about an hour the storm becomes dominated by downward motion and an ordinary storm ends, said Richardson. Although thunderstorms are a summertime phenomenon, she noted, in some rare situations a winter thundersnow can occur. This happens most often near the Great Lakes and other large bodies of water, when a cold front passes over a warm surface, causing the instability needed for a thunderstorm. If the temperature is cold enough, snow falls instead of rain.

In February 2004, thundersnows occurred in association with the blizzard dubbed White Juan, which struck Halifax, Nova Scotia, just months after Hurricane Juan had destroyed parts of that city. A low-pressure storm formed off the east coast of the United States, intensifying as it moved north. High-gusting winds and record snowfalls blanketed the whole Atlantic Canadian region. The winds, temperatures and low-pressure areas made for a perfect unstable environment.

During thundersnows, the snow dampens the thunder so it sounds like a muffled timpani drum rather than the loud cracking and booming of a summer thunderstorm. Bolts of lightning slice through the sky, creating an eerie look.

"It's kind of neat. It's not what you expect," explained Richardson who witnessed thundersnow in Wisconsin. "You can see lightning and hear thunder just like a regular thunderstorm."

Source: Research Penn State

Explore further: NASA sees Tropical Cyclone Nilofar being affected by wind shear

add to favorites email to friend print save as pdf

Related Stories

NASA sees a weaker Typhoon Vongfong near Amami Oshima

Oct 14, 2014

The once-powerful Category 5 Typhoon Vongfong has fortunately weakened to a barely Category 1 typhoon as it approaches the big islands of Japan. NASA-NOAA's Suomi NPP satellite and NASA's Aqua satellite passed ...

NASA sees Hurricane Gonzalo head toward Bermuda

Oct 14, 2014

Tropical Storm Gonzalo intensified into a hurricane late on Monday, Oct. 14 and is expected to become a major hurricane as it moves toward Bermuda. NASA's Aqua satellite saw powerful thunderstorms within ...

Recommended for you

2014 Antarctic ozone hole holds steady

12 hours ago

The Antarctic ozone hole reached its annual peak size on Sept. 11, according to scientists from NASA and the National Oceanic and Atmospheric Administration (NOAA). The size of this year's hole was 24.1 million ...

New study finds oceans arrived early to Earth

15 hours ago

Earth is known as the Blue Planet because of its oceans, which cover more than 70 percent of the planet's surface and are home to the world's greatest diversity of life. While water is essential for life ...

Magma pancakes beneath Lake Toba

15 hours ago

Where do the tremendous amounts of material that are ejected to from huge volcanic calderas during super-eruptions actually originate?

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.