Ryan Truchelut

WeatherTiger

In the last two years, I have covered nearly the full spectrum of severe weather in the Big Bend. I have needed to write about fires. I’ve produced volumes on hurricanes. I’ve even dissected 10 minutes of snow. But fortunately, I have never needed to write about tornadoes.

Unfortunately, I now need to write about tornadoes.

The severe weather outbreak of March 3 goes into the record books as the deadliest single day of U.S. tornado activity since 2013. While National Weather Service storm surveys are continuing, nearly 35 tornadoes have been confirmed in Alabama, Georgia, Florida and South Carolina as of Wednesday afternoon.

►INTERACTIVE MAP: A history of twisters: Tracking the tornadoes in Florida since 1950

The strongest was a long-tracking EF4 that killed at least 23 people across a nearly 70-mile swath of east-central Alabama and west-central Georgia.

The second strongest: the tornado that ripped a 6.5-mile-long path across eastern Leon and western Jefferson counties. Based on the severity of damage to homes in the Baum Community, the NWS rates this tornado an EF3, with maximum winds estimated at 140 mph.

The only stronger tornado and sole prior EF3 or F3 within Leon County occurred on October 22, 1945, and tore an 18-mile-long path from south of Tallahassee to Miccosukee. This twister resulted in the only recorded tornado fatality in county history. Prior to Sunday, an EF2 or F2 or stronger had not occurred in Leon County in nearly 50 years.

The Leon County EF3 was one of several strongly rotating cells embedded within an intense squall line that rolled across the Big Bend on Sunday evening.

Locally, this line also produced a confirmed EF1 tornado in Washington and Jackson Counties, an EF1 in Gadsden County just south of Quincy, an EF2 in Cairo, an EF1 southwest of Bainbridge, and a long-tracking EF0 across Wakulla County.

This means that at least four tornadoes occurred in the Florida Big Bend in one night.

This is a highly unusual outbreak for a region where climatology predicts that an EF2 or higher tornado will occur within 25 miles of a given location only slightly more than once per decade. EF2 or stronger tornadoes are much more common to our northwest, along the Lower Mississippi River Valley.

A January 2017 severe weather outbreak produced widespread non-tornadic wind damage in Tallahassee and one EF1 tornado in Franklin County, along with multiple significant tornadoes in Georgia.

While Florida averages the third-highest count of annual statewide tornadoes, trailing only Texas and Kansas, a disproportionate number of Florida tornadoes are relatively weak and short-lived EF0 or EF1 touchdowns.

These are often associated with the outer bands of hurricanes. A recent example of this type of outbreak locally is Hurricane Ivan in September 2004, which produced 13 tornadoes in the Big Bend, including a deadly EF2 near Blountstown.

Outside of tropical cyclones, Florida tornadoes are rarer than you might think for a state whose stock-in-trade is the thunderstorm. So, why don’t we scurry for an interior room every summer’s day at 3 p.m.?

The answer is that tornadoes need both changing or turning of winds with height in the atmosphere (wind shear/helicity) and rapid upward motion of air (instability).

In the tornado's path:

On a typical summer day, there is plenty of instability in the atmospheric column, allowing warm low-level air to ascend quickly into the relatively cooler upper troposphere. However, because winds aloft are typically light in the summer, these updrafts do not rotate. Without this upper atmospheric ventilation, summer storms dissipate relatively quickly due to downdrafts.

In the winter and spring, frontal systems can sometimes bring strong low-level jet streams to the Southeast, causing veering of winds with height.

This was the case on Sunday as the 7 p.m. weather balloon launched from the NWS office on Florida State’s campus recorded winds near the surface of about 10 knots from the south, and winds aloft around 50 knots from the southwest and due west approximately one and two miles up, respectively.

However, Big Bend surface temperatures are usually mild ahead of fronts in the winter, muting instability relative to summer and making it difficult for storms to tap into that kind of rotational energy to produce tornadoes in North Florida.

One reason for that is the Big Bend’s proximity to the Gulf, as winter water temperatures in the 50s and 60s can bring a stable marine layer well inland when winds are out of the south.

However, this Sunday, North Florida air temperatures soared into the lower 80s, adding ample instability on top of plenty of helicity. The unfortunate timing of the squall line’s approach in the late evening, after a full day of heating in which the sun intermittently peeked out from behind clouds, also maximized instability.

A speculative point to note regarding the unstable surface layer ahead of this outbreak: as my fellow FSU alum Dr. Andy Hazelton pointed out, sea surface temperatures in the eastern Gulf of Mexico remain two to four degrees above normal all the way south to the Caribbean Sea. As the storm inflow moved over this anomalously warm Gulf water, this may have meant a little more instability in place over the Big Bend before the line’s arrival, catalyzing explosive storm development.

As these anomalies also likely played a role in Michael’s unrelenting intensification to the coast, I think it’s safe to say we’re collectively sick of the eastern Gulf warm pool’s shenanigans at this point.

Causality aside, March 3, 2019 will be long-remembered. For those who took the brunt of the storms, it was another devastating hit from severe weather; for the rest of us, the 23 Tornado Warnings issued by NWS Tallahassee are a potent reminder to have a tornado safety plan in place before the next threat.

With another chance of severe weather in the forecast for this Sunday, be aware that just because Tallahassee has packed decades of extremes into the last two-and-a-half years doesn’t mean we’re in the clear.

Dr. Ryan Truchelut is co-founder and chief meteorologist at WeatherTiger, which provides weather and climate forecast solutions for government and private enterprise. Get in touch at ryan@weathertiger.com. A more detailed version of WeatherTiger’s hurricane outlook, with additional animated GIFs, is free to read at weathertiger.com.