Case Study - Troy, AL EF-1 Tornado

At 10:35 pm on the evening of August 6, 2015, an EF-1 tornado touched down in eastern sections of Troy, Alabama. On the ground for two minutes, the tornado caused damage to a Walmart store, destroying a tractor trailer in the parking lot.  The length of its path was .40 miles, with a width of 50 yards.

Short-lived EF-0 and EF-1 tornadoes account for a decent percentage of summer tornadoes, and are hard to predict and spot, as rotation associated with these short-lived tornadoes are typically only on 1-2 radar scans. This is a case study of the event, with a focus on radar data and Baron alerting for the tornado. In all, over 1000 Baron Safety Net alerts were distributed to the area affected by the tornado, with 14-16 minutes of advance warning–the only alerting service to provide such notifications for this dangerous storm.

 

10:18 pm
The storm that produced the tornado is to the north-northwest of the city and moving to the south-southeast. There is a Baron Severe Storm SCIT (Storm Cell Identification and Tracking) arrow located in the hook echo region of the storm.

10_18pm

 

 

 

 

 

 

 

 

 

 

10:21pm
At 10:21 pm, the storm continues to the south-southeast. Several Severe Storm arrows are associated with the storm at this time. The arrow highlighted with a storm track in the image is the arrow responsible for sending a “Dangerous Storm Approaching” alert to anyone who would have been in the Walmart where the tornado would occur 14-16 minutes later.

10_21pm

 

 

 

 

 

 

 

 

 

 

Below is a map of Safety Net users in the Troy, Alabama area. The black line indicates the path of the tornado. The high concentration of alerted locations for schools on the left is likely associated with the Pike County Liberal Arts School, which was affected by the tornado.

Pike_STN

 

 

 

 

 

 

 

 

 

 

 

Next, this map shows all issued Safety Net “dangerous storms approaching” boxes generated by severe storm arrows up to the time of 10:21 pm. The tornado path is in black, showing that anyone affected by the tornado would have been alerted at 10:21 pm.

troy_1021_alerts

 

 

 

 

 

 

 

 

 

 

 

10:29 pm
The 10:29 pm reflectivity and velocity scan shows the storm is quickly approaching the Troy metro. Reflectivity continues to show a well defined hook echo and velocity data shows a weak rotation couplet.

troy_1029_reflectivity

 

 

 

 

 

troy_1029_velocity

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The 10:29 pm reflectivity scan shows the hook echo region approaching the Walmart location. A Baron Shear Marker is present, forecasters to the presence of dangerous wind shear.

troy_1029_reflectivity_shear_marker

 

 

 

 

 

 

 

 

 

 

10:34 pm
The next three images are from the 10:34 pm radar scan, 1 minute before the official tornado touchdown time. Reflectivity data shows a well-defined hook echo in the exact location of the Walmart.

troy_1034_reflectivity

 

 

 

 

 

 

 

 

 

 

Velocity data from the same time shows a tightening circulation in the hook echo region, now apparent as radar returns are  moving toward and away from the radar–as indicated by the red “away” pixels adjacent to green “toward” pixels.

troy_1034_velocity

 

 

 

 

 

 

 

 

 

 

Baron Shear Rate reveals a high amount of wind shear in the exact location of where the tornado occurred.

troy_1034_shear_rate

 

 

 

 

 

 

 

 

 

 

10:37 pm
The following four images were taken at 10:37 pm, which is during the tornado’s time on the ground. The black line in these four images represents the location/path of the tornado. Reflectivity data shows the hook echo directly over the tornado location.

troy_1037_reflectivity

 

 

 

 

 

 

 

 

 

 

Velocity data now shows a tight couplet directly over the tornado’s location.

troy_1037_velocity

 

 

 

 

 

 

 

 

 

 

An enhanced area of shear (though not as high as the previous scan) is in the exact location of the tornado.

troy_1037_shear_rate

 

 

 

 

 

 

 

 

 

 

Resampled Correlation Coefficient (RHOHV) shows two areas of lowered measurements. The first area is in the bottom-right of the circle, and is likely associated with strong inflow into the storm. The second area is in the middle of the circle, right where the tornado was located, and possibly showing a small area of debris.

troy_1037_rhohv

 

 

 

 

 

 

 

 

 

 

10:40 pm
Shown here is 10:40 pm reflectivity scan with an NWS Tornado Warning overlaid, which was issued at 10:39 pm. This was the first NWS warning issued for the storm in Pike county.

troy_1040_reflectivity_nws_warning

 

 

 

 

 

 

 

 

 

 

10:45 pm
By now, the storm has passed the Troy metro area.

 

10:53 pm
The Baron Shear Swath product shows the high amounts of wind shear detected throughout the event.

troy_1052_shear_swath

 

 

 

 

 

 

 

 

 

 

The Baron Hail Swath shows that there may have been some hail within the storm as it moved south-southeast through the Troy area.

troy_1052_hail_swath