Beware The Cone of Silence

On Thursday night, a supercell storm developed southwest of Little Rock in Arkansas. As it moved northeast, it began to show strong indications of rotation. We were monitoring the National Weather Service Little Rock instant messaging chat. At 8:37 p.m., a tornado warning was issued for Garland, Hot Spring and Saline Counties. The storm began to get even more impressive as it moved to the northeast. The rotation began to tighten. Quarter size hail was reported on I-30.

Concern began to grow about the town of Benton, on I-30 about 9:15. The storm had excellent indications of a tornado as it approached Benton. About 9:28, damage was reported to houses along I-30. As the storm moved northeast toward Bryant, the rotation became even stronger. Amateur radio operators reported damage to a Buick dealership between Benton and Bryant.

By 9:40, concern began to grow about the city of Little Rock. The National Weather Service Little Rock is at the North Little Rock Airport There were conversations about the National Weather Service Memphis preparing to become Little Rock’s backup. Generators were started at the NWS Little Rock in preparation.

Then, at 9:53, the NWS Little Rock reported that the rear flank downdraft had snuffed the tornado and that ham radio operators chasing the storm had lost the tornado. So the storm appeared to be weakening. Warnings continued, but did meteorologists let down their guard just a bit?

The severe thunderstorm was definitely entering the “cone of silence” of the Little Rock radar. As the radar beam leaves the antenna, it travels in pretty much a straight line out into the atmosphere. The Earth’s surface, meanwhile, curves away downward from the beam as you get further away from the antenna. The further out you get, the beam is sampling the atosphere way up in the sky. At ten miles, the lowest tilt is about 275 feet off the ground. Over Hamilton, the radar beam is nearly 10,000 feet in the air!

The “cone of silence” is an area close to the radar antenna where the radar beam is not looking very high in the sky. It is a blind spot in the radar.

The storm may have pulsed briefly as it entered the Little Rock area. But it is more likely that it maintained its severe, supercell character. Damage reports began to flow in from the City of Little Rock. Cars overturned. Numerous trees and power lines down. Damage to buildings. The NWS started catching up on damage reports.

By 10:05, it was obvious that the worst part of the storm was going to pass near the NWS office. The meteorologists had to take cover as the storm passed. Winds were officially clocked at 64 mph, but the NWS reported that a tornado had passed directly over their office. Damage at the North Little Rock Airport was extensive with numerous planes overturned.

So, did the storm briefly pulse? Or were we lulled to sleep by the “cone of silence.”

This incident reminds us that we have to keep a very close eye on storms that enter the “cone of silence.” It happened yesterday to some degree on storms that were around Calera. The folks at the NWS BMX issued warnings on storms that were in the cone. As usual, another great job!

Category: Uncategorized