2011: The Year Of The EF-5

Greetings, storm chasing enthusiasts. I hope you will understand that my excitement for the new storm season is tempered with the ever-growing casualty lists from towns across the South and Midwest. When I chase storms and tornadoes, at the forefront of my mind are the people under those storms who are losing property, and sometimes their lives. We must remember to keep everything in perspective about what we are doing out there. While storm chasers are vital in documenting meteorological occurrences, in my opinion it is critical for all storm chasers to maintain a certain level of stoicism regarding the destruction wrought by storms. (Photo credit: www.tornadovideos.net)

There has been much criticism of a video released last week documenting the Joplin, MO tornado, where chasers are heard yelling profanity-laced descriptions in the background. Granted, that tornado was huge, and bound to generate excitement. However, many professional and scientific chasers thought the verbiage was inappropriate, considering how many people lost their lives in Joplin, (125 as of this posting). I will tell you from personal experience that it is difficult to control one's emotions in the presence of such violent weather, so I see both sides of the issue. As storm chasers, we have to decide what is, and more importantly what is not, appropriate behavior, when we release storm video.

2011 is on track to become a record tornado year for the United States, not only in the number of tornadoes, but also in the number of EF-5s being recorded. The Joplin tornado was upgraded to an EF-5 yesterday (May 24, 2011).

If you are unfamiliar with the "Enhanced Fujita" or EF scale, please hit this link:
http://www.spc.noaa.gov/faq/tornado/ef-scale.html

Several EF-5s were recorded in last month's outbreak across Alabama, Tennessee and Georgia.

Why are this year's tornadoes so violent? First, the interaction between storm systems and the Jet Stream has made for several outbreak situations in recent weeks. Often in the early to mid spring, the Jet Stream is still far enough south to coincide with the passage of low pressure and frontal systems. The Jet Stream is a major player in thunderstorm evolution. If we get an active Jet Stream flow (50 knots or higher) above an area primed for thunderstorm growth, some of the major storm elements become enhanced. Speed and directional shear, and lift, are increased by strong Jet Stream winds. In the case of the recent tornado outbreaks, the Polar Jet, which circles the Earth at 7-12 km (23,000 - 39,000 feet) and separates major cold and warm air masses, was present. Digging further into this phenomenon, there were significant "jet maxes" crossing the prime thunderstorm areas during the outbreaks. A jet max is an area of particularly strong winds, embedded within the Jet Stream itself, say over 110 knots. In meteorology, we divide jet maxes up into quadrants, so picture an oval divided into quarters. In the left-front and right-rear quadrants of a jet max, we often see enhanced lift and shear.

The recent weakening of the La Nina phenomenon in the Pacific may also be a contributor. During La Nina springs, a large ridge forms over the western USA, serving to push the jet stream farther north. La Nina has weakened significantly in recent weeks, and the Polar Jet Stream has stayed far to the south. This means the Jet has been crossing the Deep South and the Southern Plains, and interacting with thunderstorms more frequently than usual.

Strong Jet Stream winds in the vicinity of large thunderstorms serves to enhance lift by evacuating air from the top of the thunderstorm. This air must be replaced with something, and often air is pulled from below, thereby enhancing lift. Shear is also enhanced because the Jet Stream usually provides strong southwesterly winds in the mid and upper levels. Combined with adequate surface winds from the southeast, the two wind vectors cross each other and give a "twist" to the atmosphere within a thunderstorm, enhancing growth and severity.

Many storm chasers I speak with are expecting a very active June for Colorado's eastern plains. We will be out there, providing images, video and accounts of whatever takes place.