No Place on Earth
can put the ingredients together for an outbreak of tornadoes quite like the central U.S. and the outbreak of May 10th, 2010 certainly reminds us of this fact.
Rope Tornado Near Yukon, OK. Photo by Chris Novy.
The outbreak came together as extremely unstable air was pulled northward ahead of a dry line. At the same time, a very strong but compact area of intense air level winds (shortwave/jet max) moved over the area.
The alignment of the upper level winds and unstable air was going to last for only about six hours and in a relatively small area. But in that time and space frame, numerous supercell thunderstorms quickly evolved, most into tornado-barring cells.
At this writing, the National Weather Service in Norman, Oklahoma has indentified ten areas where tornadoes likely tracked on this day. More tornadoes occurred in Kansas and northeastern Oklahoma. This will be refined more as survey crews finish their painstaking task. The death toll stands at five.
NWS Reviews:
The Set Up
Low Wall Cloud, Multiple Vorticies. Photo by Allan Detrich.
It was a situation typical to the Great Plains but with the volume cranked way up. It starts when a “trough” of low pressure develops over the western U.S. This encourages steady southerly winds to blow over the central U.S. drawing humid air from the Gulf of Mexico northward. On this day the dew points, a measure of moisture in the atmosphere, were quite high and this humidity helps to make the air unstable. In fact, all else being equal, higher dew points will generally lead to more violent storms.
Unstable air is produced whenever you can warm the air at or near the surface of the earth while keeping things relatively cool aloft. Moisture adds to the instability because when water vapor condenses back into visible cloud droplets, the energy in took to evaporate this water is released into the atmosphere.
Now on top of all of this, the jet stream winds, fueled mostly by differences in temperature from south to north, were howling! These winds do several things. The overall increase in wind speed with increasing height provides structure for developing thunderstorms and allows them to become “supercells”. Also, the speed and directional changes in the wind close to the earth’s surface provide a spinning which the updrafts of a thunderstorm inherit.
Sometimes, the “wind shear” can be too strong and developing storms will get “sheared” off. The winds on the outbreak day were strong enough to be a concern for this happening BUT the instability was so strong that the updrafts which make up a thunderstorm rose violently and were able to survive, even flourish, in this environment!
Chasing These Storms
The wind speeds were very high in the atmosphere leading to storms traveling over 60 mph! This “storm motion” made these storms difficult to chase. Still, there were some shots. The multiple-vortex tornado shot by Andy Gabrielson is stunning!
Some local chaser friends of mine Jason Blum, Dave Toner and Cody Hudson got themselves into a dangerous situation near Arkansas City, KS. Their vehicle goes down a steep embankment. Then the tornado passes nearly on top of them!
The Ozarks Missed This
Some may wonder since weather moves from west to east why the Ozarks didn’t see at least a weaker version of what happened out west, especially considering how fast the jet stream was. The answer is that we were in much more stable air. I watched as these storms literally fell apart while racing eastward. The fast jet stream winds actually outpaced the ability to draw unstable air out ahead of the system. Later on, we actually did have a tornado warning or two west and northwest of Springfield but this was mostly due to the incredible wind shear working on even the weakest updraft to see if can be coaxed into rotating.
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