Devastating Tornado Outbreak Across the South

On Friday afternoon, Contributor Evan Hatter previewed what was likely to be a pretty substantial severe weather outbreak across the southern US over the weekend. Models had been hinting at it for several days by that point, and they were honing in on a multi-day, multi-round severe weather episode across much of the south, extending from Texas to Georgia.

The storm reports from Friday and Friday night. h/t SPC
The storm reports from Friday and Friday night. h/t SPC
The storm reports from Saturday and Saturday night. h/t SPC
The storm reports from Saturday and Saturday night. h/t SPC
The storm reports from Yesterday. h/t SPC
The storm reports from Yesterday. h/t SPC

Unfortunately, it was worse than it was initially thought to be. Multiple rounds of severe weather developing in the late evening hours and lasted into the overnight hours. These took advantage of inherently greater shear at night (stronger low level jet), and produced overnight tornadoes, which are extremely dangerous.

Add in that this took place in the south? There was a bad combination for tornadoes and damage. The south isn’t populated as densely with cities, but small towns are all across the region. Line a tornado up with one, and you have some major issues, especially at night. Over the weekend, there were about 41 tornadoes reported, and 20 deaths. The last number is more tornado-related deaths than were seen in all of 2016.

2016 had 17 tornado deaths all year. 2017 has already had 20 reported tornado-related deaths. h/t SPC
2016 had 17 tornado deaths all year. 2017 has already had 20 reported tornado-related deaths. h/t SPC

So why did this happen? Well, first of all, looking from the synoptic atmosphere, there was a strong, elongated longwave trough that was centered from the northwestern US southeastward in the south-central US. This allowed for shortwave troughs to ejected around the base of this trough all weekend, and it provided enhanced mid and low level winds all weekend.

The progression of the 500 mb flow since Friday. h/t SPC
The progression of the 500 mb flow since Friday. h/t SPC

By the end of the weekend, a very strong jet streak had ejected from the west coast and into the southwestern US, and this began to deepen a mid-level low across the south-central US. This had enhanced jet streak features with it as well, and led to the set up that we saw yesterday, that led to a High Risk of severe weather.

Yesterday was the first time that a High risk had been issued since 2014. h/t SPC
Yesterday was the first time that a High risk had been issued since 2014. h/t SPC

An enhanced upper-level jet streak let to the deepening of the low pressure at all levels of the atmosphere yesterday, leading to further enhancement of the wind fields in the mid and lower levels of the atmosphere.

The 850 mb temps, winds and dewpoints yesterday afternoon. h/t SPC
The 850 mb temps, winds and dewpoints yesterday afternoon. h/t SPC
The 0-3km Storm Relative Helicity was ridiculous yesterday. h/t SPC
The 0-3km Storm Relative Helicity was ridiculous yesterday. h/t SPC

This led to high amounts of wind shear throughout the atmosphere, enhancing the threat for a tornado outbreak. At the surface, an anomalously moisture rich environment was the real deal. That was really the characterization of the lower atmosphere and near surface conditions. Moisture streamed northward from the Gulf of Mexico, and created very unstable conditions across much of the south by Sunday.

The environment yesterday was crazy. h/t SPC
The environment yesterday was crazy. h/t SPC

Why was such anomalous moisture present? Well, cold fronts really haven’t had the chance to clear the southeast into the Gulf of Mexico. This has allowed the waters to remain warm, and air over them moisture rich.

The result was a bad tornado outbreak. There were deadly tornadoes on all three days, as bigger towns were struck by tornadoes. Hattiesburg, MS was struck during the overnight hours of Friday, and Albany, Georgia was struck yesterday afternoon by a strong tornado.

Keep the families and affected folks in your thoughts and prayers going through the next few days. Cleaning up after a terrible tornado outbreak is never fun, and it is especially not fun when 20 people passed away from related injuries.