Much of the recent cold and snow can be blamed on excess moisture in the atmosphere and an expanding polar vortex — a large area of low pressure and cold air surrounding both of the Earth’s poles. It always exists but strengthens in winter. “Vortex” refers to the counterclockwise flow of air that helps keep the colder air near the poles. In the Northern Hemisphere, the polar vortex expands many times during winter, sending cold air southward with the jet stream.
Winter storms have three basic ingredients: moisture, lift, and cold air. Moisture forms clouds and precipitates as rain or snow. Air blowing across a body of water, such as the ocean or a large lake, is an excellent source of moisture. Moist air must be lifted to form clouds and cause precipitation. For example, warm air colliding with cold air is forced to rise above the cold dome. The boundary between the warm and cold air masses is called a front. Another example of lift is air flowing up a mountainside. Below-freezing temperatures in the clouds and near the ground are necessary to make snow or ice.
The rising water vapor eventually cools and converts back to a liquid. The resulting water droplets can create clouds, provided they have something to condense onto, much like dew condenses onto grass or water condenses on the outside of a cold glass. The atmosphere contains aerosols — microscopic particles that occur in nature and can also be generated by human activity: mostly bits of dust, dirt, and salt. These aerosol particles serve as condensation nuclei for water vapor in the atmosphere. Atmospheric water molecules drawn to aerosol particles form water droplets that create a cloud. Without aerosols, clouds could not exist. Clouds play an important role in regulating Earth’s climate: Aerosol-rich air masses generate bigger, brighter, and longer-lasting clouds.
Storm clouds tend to billow up as they grow, towering into colder and colder regions of the atmosphere. Most clouds still consist of liquid water droplets, even during frigid periods. They begin freezing around 14 degrees Fahrenheit. Individual cloud droplets solidify into ice particles that attract more water to their surface, creating tiny but fast-growing “snow crystals,” which fall when they become heavy enough.
Snow crystals grow into diverse shapes depending on the cloud’s temperature and humidity. They collect more and more ice particles as they drop through the cloud, and often clump together. By the time these falling crystals exit the cloud’s base, they’ve usually grown into “snowflakes.”
If the air is below freezing all the way down to the surface, these flakes keep their distinctive patterns and accumulate on the ground as snow. Snowflakes that melt while falling become rain. If that rain refreezes before landing, it forms “sleet.” If it refreezes only after it lands, we have “freezing rain” that coats roads and sidewalks with a slippery coat of ice.
On average, 105 snowstorms hit the U.S. each year, producing snow for up to five days across several states. Almost every part of the country sometimes sees at least mild flurries — even South Florida — but snow falls so irregularly that no official snowfall records are kept at state levels. Local-level totals, however, suggest New York as the home state of some of the country’s snowiest cities. Syracuse averages 115 inches annually, followed by Buffalo (93), Rochester (92), and Binghamton (84). Among less populated areas, Mount Washington, N.H., averages 275 inches, and the Paradise ranger station in Washington’s Mount Rainier National Park leads the nation with its annual average of 677 inches.
Snow is pretty but also a problem. In addition to threats like frostbite and hypothermia, snowstorms strand commuters, close airports, and disrupt emergency services. Large snow buildups topple trees, snap power lines, even cause roofs to collapse. According to a recent study, increasing snowfall in Europe is at least partly linked to climate change, since the loss of Arctic sea ice lets more cold air flow southward.
I have learned my own lessons about Maine snowstorms as well. For the third time last week, before I got to it, neighbors shoveled out my walk and driveway. (I still don’t know who did it the first time three years ago.) A few years farther back, with my foot in a cast, my pickup truck slipped off the pavement. Within a minute, three pickups stopped and the drivers pushed me back on the road. Mainers. We also stop to let you cut in when traffic is heavy. And we wear our face masks to protect each other, too.
Happy and safe holidays to all!
(Paul Kando is a co-founder of the Midcoast Green Collaborative, which promotes environmental protection and economic development via energy conservation. For more information, go to midcoastgreencollaborative.org.)