Understanding the Complexities of Wintry Precipitation in the South

The most significant snowstorm in years roared through a large swath of the southern U.S. at the end of last week, bringing everyday life to a screeching halt. Here is a more detailed look at the unique combination of snow and ice in this part of the country.

Looking Back at Last Week's Winter Event in the South

A massive winter storm dumped accumulating snow, freezing rain, and sleet over more than a dozen U.S. states last week. Almost 53% of the U.S. had snow on the ground on Sunday morning thanks in large part to a rare winter storm that sent the flakes flying in places such as Georgia and Mississippi. In fact, as of Sunday morning, there was more snow covering the ground in the northern parts of Mississippi, Alabama, and Georgia than there were in states such as Iowa and Wisconsin.

The storm fired up early Thursday in parts of Texas, Oklahoma, and Arkansas. Dallas Fort Worth International Airport experienced severe disruptions, with over 2,000 flights cancelled over a two-day period.

Residents of the South who are enjoying the snow will appreciate that it is likely to stick around for some time. This part of the country is forecast to see temperatures fall as much as 20 degrees below the historical average over the next few days, keeping the snow on the ground for longer.

How Ice and Snow Develops in the South

Like any part of the world, the South needs the right combination of elements from Mother Nature for snow and ice to form. The South is typically flush with an abundance of moisture at regular intervals thanks to its proximity to the Gulf of Mexico. What the region does not see as often is air that is cold enough to support the development of wintry precipitation.

The southern tier of the U.S. needs the polar jet stream to dive far enough to the south for snow and ice to come together. This generally happens a few times each winter season. The cold air needs to be hovering close enough to the surface of the ground for snow, sleet, and freezing rain to generate.

Another setup that promotes the development of wintry precipitation happens when a strong low-pressure system sets up near the Gulf Coast or across the coast of the Southeast. This scenario is less likely than the typical intrusion of cold air from the north meeting up with the moisture-rich air coming up from the Gulf of Mexico.

When Winter Storms Are Most Likely to Erupt in the South

You are most likely to see winter storms form in the South during the months of January and February. This is when the necessary ingredients are most likely to take root. An active weather pattern to the north promotes a more regular pattern of wintry precipitation to the south during this time of the year. That said, the South has also seen the appearance of snow as early as the late fall and as late as March.

Diving Into Average Snowfall Totals

Most communities in the South see snow once every other year on average. However, accumulations are typically limited to less than an inch. Metro areas such as Jackson, Mississippi; Charleston, South Carolina; and Montgomery, Alabama pick up snowfall of an inch or less on average each year, according to data over the last few decades.

While the region does not usually see monster storms like the past week, the snowfall totals add up over the course of a season. For instance, Raleigh, North Carolina picks up an average of 5.2 inches of snow throughout the entire season. The higher terrains of North Carolina is even snowier with places such as Asheville averaging 10.3 inches of snow in a season.

Moving farther to the south, Atlanta averages just over 2 inches of snow throughout the season. Nashville comes in with an average of 4.7 inches in total each winter.

As with all weather events, there are seasons that serve as outliers. Nashville saw a whopping 38.5 inches during the winter of 1959 - 1960. That same snowy season brought 56.7 inches of snow to nearby Knoxville, Tennessee.

The average snowfall totals tend to dip heading closer to the warmer waters of the Gulf Coast. The snowiest season in New Orleans happened during the season of 1963 - 1964 when 2.7 inches fell. The greatest snowfall total for one single season in recorded history in Houston happened in 1973 - 1974 when the city saw 4.8 inches of accumulation.

Dangers of Ice

Although snow is rare in the South, this region is more vulnerable to the impacts of sleet and freezing rain. How the precipitation falls is dependent on the temperatures at various levels of the atmosphere. The moisture comes down as snow when the mercury readings are below the freezing level at the surface of the ground and in the upper levels of the atmosphere.

Conversely, freezing rain or sleet is more likely to form when the temperatures close to the ground are measuring below the freezing mark but the air a few thousand feet high is warmer. Sleet happens if the precipitation refreezes prior to reaching the ground. Meanwhile, freezing rain is the situation if the moisture freezes on contact with the cold ground.