Detecting Storm Rotation on Radar : an examination

Disclaimer: This post is for educational purposes and in no way is meant to flame or discredit the fine local meteorologist. They do a great job!

First a little history for the reason of this post.

On June 17 2011 we had some storms move through the area. The Emergency Alert System [EAS] better known to many as Tornado warning siren went off in Columbus Georgia. Once again there was no official warning issued by the National Weather Service [NWS]. Many again wonder why it went off. At the time some rough weather causing damage to our west in Alabama was being reported in Phenix City.

This is the E-Z Car wash on hwy 80 next to Zebs in Phenix City. Image Credit Skye Cameron Brown

I was watching the radars for any sign of severe weather. I commented on the picture above on Facebook:

Thats crazy. Maybe this is why the sirens went off in Columbus. Also, I took a couple screen shots of radar and may see what appears to be a hook echo on composite, and rotation on velocity. I’ll get them loaded tomorrow.

Others also commented, even the original poster which is one of our local meteorologist, so I loaded them the same night. Here is the conversation that followed. Names left out to protect the innocent. The local met will be denoted with WEATHER.

WEATHER: Cataula… What radar site were you using?
Yesterday at 6:36pm

Cataula Ga Weather: NWS – FFC Composite and MXX Storm Relative
Yesterday at 6:47pm

WEATHER: Interesting… because I don’t see a hook echo at all within the past three hours. I see areas of extended rain where the downdrafts were pulling the rain further ahead though.

Cataula Ga Weather: give me a minute and I post them on my wall
Yesterday at 7:03pm

Cataula Ga Weather: radar shots are up
Yesterday at 7:42pm

WEATHER: Cataula, I don’t see a hook echo in the radar or relative velocity. The inbound winds (green) along the county line there was the inflow jet that got the line to basically bow out. This wasn’t a classic case, but it was just the southern edge of the line trying to catch up to the northern half.

Kevin is correct in his remarks about the atmosphere not primed to produce a mesocylone. We generally see those with discreet supercell thunderstorms (like the April 27th event). Also, the shear wasn’t nearly conducive to allow the formation of a tornado.

Many people experienced the winds rushing from the top of the thunderstorms and this brought the clouds closer to the ground, giving the illusion of a tornado.
Yesterday at 7:56pm

Cataula Ga Weather: Thats why you’re the pro. Sure looked like rotation to the untrained eye. That being mine.
Yesterday at 8:01pm

WEATHER: No problem Cataula! That’s why we are here.

Not being one for argument as I’m only a weather hobbyist, I left it at that. But now I want to examine the images I posted further.

As stated in the conversation, I was viewing the radars ‘FFC Composite Reflectivity and MXX Storm Relative Motion’. FFC is radar from NWS Peachtree City Georgia, and MXX is from Maxwell Air Force Base in Alabama. Here are the images, unedited as they are on Facebook. FFC Composite Reflectivity on left and MXX Storm Relative Motion [velocity] on right.

As you can see in the image on the left, I circled an area where I see a possible hook echo. I circled a large area so as not to obstruct the surrounding storm. The hook I am speaking of can be seen at the bottom in the county that Auburn is in. Here it is in this edited image, yellow arrow pointing to it.

In the image on the left [from above]taken a moment after the first you can see the ‘red’ just below Aurburn. Here it is edited, yellow arrow pointing to it.

Again from the above conversation the meteorologist said:

WEATHER: Cataula, I don’t see a hook echo in the radar or relative velocity. The inbound winds (green) along the county line there was the inflow jet that got the line to basically bow out. This wasn’t a classic case, but it was just the southern edge of the line trying to catch up to the northern half.

This may still be the case as he is the one with the proper education. I still see a hook in the Composite Reflectivity and Rotation in the Velocity image. I never said Tornado which was mentioned in the conversation.

In all velocity images, red colors indicate wind moving away from the radar with green colors representing wind moving toward the radar. It is very important to know where the radar is located as that is your reference point for proper interpolation of the wind’s motion. As mentioned, I was viewing the velocity image from MXX from Maxwell Air Force Base in Alabama. Here is it’s location.

As you can see it is located around Montgomery Alabama, well west of the target rotation in the above velocity image. Regardless, where you see red and green come together, that is an area of wind rotation. Correct me if I’m wrong.

I didn’t get to the Georgia storm reports from National Weather Service Peachtree City, GA [FFC] before they were removed. I wish FFC kept the information up longer like National Weather Service Birmingham, AL [BMX] does.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BIRMINGHAM AL


0325 PM TSTM WND DMG LADONIA 32.46N 85.09W
06/17/2011 RUSSELL AL BROADCAST MEDIA

AWNING BLOWN OFF OF CAR WASH ALONG HIGHWAY 80. TIME
ESTIMATED FROM RADAR.

---------

0322 PM TSTM WND DMG 5 W PHENIX CITY 32.47N 85.10W
06/17/2011 RUSSELL AL PUBLIC

LARGE TREE DOWN ON COUNTY ROAD 208 NEAR HIGHWAY 80
COMPLETELY BLOCKING THE ROAD.

---------

0255 PM HAIL 3 SE OPELIKA 32.62N 85.34W
06/17/2011 E1.00 INCH LEE AL EMERGENCY MNGR

You may have caught the mention of ‘mesocylone’ and ‘inflow jet’ in the above conversation.
A mesocylone is a vortex within a convective storm and has air that rises and rotates around a vertical axis. Most of the time this is associated with a ‘supercell’ thunderstorm. Sometimes the winds become violent enough to produce what we call a tornado. Sometimes they don’t, such as the case here. Still, there was rotation in the storm I’m talking about.
An inflow jet is cooler air at the surface and warmer air aloft created from convection. This can create what is known as a ‘Bow Echo’ and is usually associated with ‘straight line winds’, which is what caused the damage around the area on June 17.

Here are some more images of the storms as they pushed through.

Image Credit Mathew Cook

Image Credit Mathew Cook

Image credit Bob Jeswald WRBL

Image credit Bob Jeswald WRBL


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