The January 23-26 system dumped snow and crippling ice from New Mexico to Maine, with some of the worst effects felt in the South, and it was linked to more than 100 deaths.

But according to the National Oceanic and Atmospheric Administration (NOAA), the storm ranked only as a Category 3, or "major," on the Regional Snowfall Index (RSI) -- a scale that measures the societal impact of snowstorms from 0 to 5 and has been calculated back to 1900.

Category 5 storms are extremely rare, accounting for about one percent of events classified as "extreme," while Categories 0 and 1 are common, together making up 79 percent of storms.

Last week's system reached Category 3 levels in the Ohio Valley and the South, Category 2 in the Northeast, Category 1 in the Southeast, and Category 0 in the Upper Midwest and Northern Rockies and Plains.

"Snowstorms are complex and impacts can be determined by a number of varying factors, which makes communicating the severity of a snowstorm challenging," John Bateman, a NOAA meteorologist, told AFP.

"For the Regional Snowfall Index (RSI), the area of snowfall, the amount of snowfall, and the number of people living within the snowfall boundaries are used to determine a range of impacts."

By comparison, the "Blizzard of 1996" was a Category 5 storm that struck the Northeast in January of that year, affecting more than 58 million people. The "Groundhog Day Blizzard of 2011" impacted four regions and reached Category 5 intensity in the Ohio Valley and Category 3 in the South.

More notable than the snowfall itself was the prolonged blast of extreme cold that followed, hardening snow into what has been informally dubbed "snowcrete" and making cleanup efforts especially difficult.

Another storm hit the South over the weekend, with cold-stunned iguanas falling from trees in normally mild Florida, while the city of Lexington in North Carolina recorded 16 inches (40 centimeters) of snow.