Historic Deep South snow: The science behind it
TAMPA, Fla. (WFLA) — Parts of the Gulf Coast measured a foot of snow on Tuesday. For many cities, the totals obliterated long-standing snowfall records. Milton, Florida recorded 9 inches of snow, which more than doubles the all-time statewide Florida record of 4 inches.
The heaviest snow fell in Louisiana, where the city of New Orleans piled up 10 inches of snow with isolated reports of over a foot. And Mobile, Alabama also shattered their record, picking up around 8 inches.
Heavy snow was still falling Tuesday night in northern Florida, where Tallahassee had a chance to break its all-time record snowfall of 2.8 inches. Snow and ice had been forecast to fall across the I-10 corridor into Lake City and Jacksonville, with perhaps a few ice pellets as far south as Ocala. All precipitation was set to end by daybreak.
Temperatures were expected to fall below freezing from Citrus County northward. Patches of ice on roads were to become more prevalent the further north you go from there.
So what was causing this bizarre weather system? It was due to a unique setup in which very cold air was being forced south into the Gulf, while warm, moist air was being propelled above it by a stalled front and weak low pressure over the Gulf.
This was all happening because the polar jet stream is stuck over the Gulf Coast, being forced thousands of miles south of its normal location by a displaced Polar Vortex. That Polar Vortex, normally far north in Canada, is positioned in the northern U.S. — forced south by very warm air over the Arctic Ocean. It's all connected.
The position of the jet stream over the Gulf is activating a stalled front, initiating development of low pressure (and moisture) while all the cold air is being forced south.
The result is what we call "overrunning," where the warm air is forced north by low pressure, and because it is lighter (and cold air is heavier/denser), the warm air "overruns" the cold air at the surface. That lifting of the warm, moist air creates clouds and precipitation. Since it is cold enough for snow, that is what was falling.
The snow was made heavier by very warm water in the western-central Gulf -- in some cases, about 5 degrees above normal.
Some people may mention climate change — either that this event proves it exists or does not exist. This event proves neither. There's no way of knowing whether this event would have occurred or not without climate change.
What is known is that the warmer air in the Arctic influences the further south displacement of the Polar Vortex and the warmer Gulf produced heavier snowfall rates than it otherwise would have.
Jeff Berardelli is WFLA's Chief Meteorologist and Climate Specialist