Some new information about the Branson tornado.
First, George Fair has put together a very detailed, 3D fly-over in Google Earth of the track of the Branson tornado. Included are comments about the intensity of the storm, landmark identification and pictures/movies of the damage at key points along the path. I’ve included the video in this post.
This is a good place to remind folks that the EF (Enhanced Fujita) tornado scale is an estimation of wind speed based on observed damage. Therefore, the rating can only be applied to areas receiving damage. Everyone must remember that comments about a tornadoes’ intensity without damage or detailed data to support might be a slipperly slope!
National Weather Service radars are presently receiving an upgrade to their software across the country. Springfield’s radar just received this upgrade back in February. It’s called Dual Pol where “Pol” is short for Polarization.
When a radar beam is sent out, there is a horizontal and vertical component to the wave. When used in conjunction, these can be used to detect the proportional shape of the “target” (rain, snow, hail) measured in width and height. Example: Dual Pol can in theory identify something that is more round (height/width about equal) as opposed to more oblong (width greater than height). When used with other information, this can lead to the identification of precipitation types and can also be used to see the difference between “weather” and “non-weather” targets.
I’ll be providing you with more information on Dual Pol and how it can help meteorologists over the next few weeks but let me jump now to a fascinating if not somewhat surreal application of the technology with regard to tornadoes.
Lately, the term “debris ball” has come into common usage when describing a radar echo suspected of producing a tornado. The “ball” portion refers to the appearance on radar. The “debris” part is as it sounds; tornado damage, pieces of whatever the tornado is destroying, lifted into the air high enough for the radar to detect.
Sometimes in extremely powerful storms like Joplin, the debris ball is obvious for what it is on ordinary radar, especially when backed up by ground observation or by a particularly strong rotation signature on radar.
But in weaker signatures like the Branson tornado, Dual Pol can help to verify a tornadoes’ existence. One thing the software can do is report the “randomness” of height vs. width changes on what the beam is striking from pulse to pulse. Tornado debris varies in shape and size greatly and is flying around fast when compared to most precipitation therefore it becomes easy to spot.
Here is an example of a four panel radar from when the Branson tornado had just past the downtown portion of the city. There is a “velocity couplet” (the reason for the warning initially) but there is also evidence of a debris ball showing up in the Dual Pol panels on the left side!
While this technology has limited use for tornado warning lead times, it certainly can be used to affirm that a tornado is occurring! This would lend more credence to a tornado warning and help forecasters decide how to proceed as the storm moves.
Here’s another write up on debris balls and dual pol from The Weather Channel.