Wednesday, April 17, 2019

April 13-14, 2019 southern states tornado outbreak

The April 13-14 tornado outbreak across the southern states killed 3 people due to tornadoes (2 in Texas, 1 in Mississippi) and, sadly, several others died due to wind and flooding.  Tornado-wise, there were at least 10 EF2 tornadoes and 2 EF3 tornadoes on the 13th.  

The tornadoes pictured above were near Hearne, Texas (EF3) at late morning, and at Vicksburg, Mississippi at late afternoon.  Damage is also shown in east-central Texas between Weches and Alto where 2 people lost their lives in a tornado around noon-time.  Unfortunately, two children also died nearby in a vehicle from a falling tree in severe thunderstorm winds. 

The outbreak was forecast well by NWS meteorologists, the third deadly tornado outbreak across the South in 2019.  I won't do a detailed analysis here, as there was nothing particularly unusual about it.  But I did want to point out how most of the strongest tornadoes occurred with storms near and just south of the warm front that moved from east-central Texas to northern Mississippi during the day.

Severe weather forecasters know very well that the zone along and near warm fronts tends to have increased low-level shear with backed (more easterly) surface winds, so if strong warming and moistening is also occurring in that area, it becomes a favored location for supporting tornadic storms.  That can be seen on the graphics below showing warm frontal locations and the SPC effective-layer significant tornado parameter:

Even though environments well south of the warm front also looked favorable for tornadoes, the area along and just south of the warm front tended to provide the focus for most of the tornadic storms in this outbreak.

The associated upper system plowing across Texas and into the Dixie states was strong, with an intense 500 mb trough (indicated by thick red dashes):

So, along with this strong upper system, the strong surface warm front and unstable/sheared environment ahead of the surface low generated a number of tornadoes.

Even with a strong southern jet stream propelling storm systems across the southern U.S. so far this early spring, periodic intrusions of cold air from Canada from a northern branch jet stream over the Great Lakes have kept tornadoes away from Kansas and Oklahoma so far in 2019 (Kansas is off to it's 4th slowest start for tornadoes since 1990, similar to last year).  We'll see if that changes soon.

- Jon Davies  4/16/19

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