FIG. 1For a tornado to possibly evolve, scientists know that another set of parameters must also be present within the pre storm environment. Those being moisture and shear. Deep rich low level currents of moisture from the Pacific, Gulf of Mexico, and subtropical Atlantic flow northward across the southern and central states, and eventually into the northern plains and our coverage region. As this moisture plume surges northward, it will often meet with, and collide with colder and drier air from Canada. When this occurs, a "battle zone" is created typically along and ahead of boundaries known as "fronts". This is where the atmospheric fireworks begins. While not shown in figure 2, we do see the flow currents of warm, moist, and unstable air northward.
FIG. 2As the flow of deep-rich moisture laden air continues streaming northward, the environment begins to destabilize as the sun heats the surface of the earth. As previously mentioned, this warm and moist air mass is less dense then cold air, so it can rise freely into the atmosphere. As it does so, the rising air currents intersect with currents flowing in a different direction at a different height. This results in a "tube" or column of air which spins about a horizontal axis. As more rising warm air pushes upward, it begins to "pull" the rotating horizontal column upward, and eventually into a near vertical axis. Figure 3 shows this column of rotating horizontal flow, and figure 3a shows how it becomes stretched into a near vertical fashion.
|CAPE||WHAT IS POSSIBLE|
|0-1000 J/KG||Widely scattered thunderstorms possible. No severe storms likely.|
|1000-2000 J/KG||Scattered severe storms. Isolated tornadoes possible.|
|2000-3000 J/KG||Scattered to numerous severe thunderstorms, including super cells capable of all facets of severe weather.|
|3000-4000 J/KG||Numerous to widespread severe thunderstorms, including tornadic super cells capable of all facets of severe weather.|
|4500+ J/KG||Widespread violent super cells and tornadic super cells likely.|
|Energy Helicity Index||Severe Elements|
|Greater then 1||Potential for super cells|
|1 to 5||F-2 to F-3 tornadoes possible|
|Greater then 5||F-4 to F-5 tornadoes possible|
|0||No Cap Present|
|0.1 - 1.9||Weak Cap|
|2.0 - 4.0||Moderate Cap|
|Greater then 4.1||Strong Cap|
FIG. 6Their are three (3) stages of a thunderstorm's life cycle, the developmental stage, the mature stage, and the dissipation stage. We have already examined some of the factors which can breed severe thunderstorms, and yes, even tornadoes. We have covered a number of severe weather parameters used by forecasters to asses the existing state of our atmosphere and determine it's potential to produce severe storms. But any thunderstorm that develops will have these three stages of it's life cycle. Figures 7, 8, and 9 below illustrate the three stages.
FIG. 10Forecast progress into the early 1960's continued at SELS as continued research led to more parameters which proved useful to the prediction of severe storms. Then, in April of 1963, a new IBM 1620 computer system was installed at SELS. This new computer system allowed forecaster to plot and analyze weather charts much quicker then by manually doing them as was the case before. In addition, this system allowed forecasters the added benefit of accessing diagnostic fields of convergence and divergence that were difficult or impossible to manually compute. Then, in November of 1965, another new computer system, the CDC 3100 was installed. This gave the additional benefit to automatically analyze and plot both surface and upper level data and charts. The district offices could also have access to this system for data tabulation and research work. These two pieces of technology of the time gave forecasters the badly needed break to help them prepare and issue more accurate forecast products. Forecaster confidence, skill, and experience also benefited their products. In 1966, changes were in store for the forecast and bulletin products. The severe weather forecasts were renamed to "Convective Outlooks", and the severe weather bulletins were renamed as "Tornado or Severe Thunderstorm WATCHES". This change was so that these products conformed better with similar products being issued by the NHC or "National Hurricane Center. In addition, SELS was renamed to the NSSFC or "National Severe Storms Forecast Center". This name change was done to better reflect the national scope of the agency. Figure 11 shows the National Severe Storms Forecast Center in 1967, a year after it's agency name change.
FIG. 11In 1968, the National Severe Storms Forecast Center assisted with the creation of two additional agencies. The first, was a joint effort to launch an agency to conduct laboratory researches into the causes of severe local storms, and the environments which triggered them. Thus, the NSSL or "National Severe Storms Laboratory" was born. Later that same year, another agency, not part of NOAA, was also created. This agency was comprised of local storm spotter groups from every state, who took the time to go out and monitor weather and sky conditions whenever a watch was issued by the NSSFC for their areas. The idea here, was to report any kind of severe weather elements (i.e. large hail, damaging winds, or tornadoes), they observed to the Weather Bureau district offices. This agency was known as "SKYWARN". Then in early 1969, the NSSFC had issued a policy which made it clear the elements which defined a severe thunderstorm (those are mentioned above for reference). Because of the spotter groups, many folks in their respective communities became interested in and attended special group meetings where trained spotters and staff from area Weather Bureau district offices would explain what thunderstorms were, how they develop, and the elements of a severe thunderstorm. They also offered classes for those who wanted to become spotters free of charge. Sky warn still operates today, in conjunction with other groups. In 1970, the U.S. Weather Bureau was officially renamed as the "National Weather Service", and put under the Commerce department. Over the next 30+ year period, numerous advances in computer technology, local research and field studies of data collected in pre storm weather environments, and data from tornado "probes", allowed for vast improvements with existing forecast and watch products. While their were some occasions where false reports were received by the NWS generating needless warnings, the number of verified reports outnumbered the false reports. This along with the already badly aged WSR-57c radar systems became a serious problem with both watch and warning issuances. Under existing circumstances, the radar would indicate thunderstorms, but no way of knowing their intensity, unless reports came in of severe weather. This occasionally would result in "missed" warnings, or late warnings being issued. The average lead time for tornado warnings was only 3 minutes. Figures 12 and 13 shows this badly aged WSR-57c radar tower and indoor counsel unit.
FIG. 15There is also some other things you and your community can do to help minimize the dangers of not only tornadoes, but the other destructive elements often associated with severe thunderstorms. If you don't know about severe weather safety, you can always go online on the Internet, and search for the closest NWS website near you. No doubt, they can provide you with all the necessary facts and information (publications are also available for download). You can also take our in-house severe weather safety quiz to find out what you know about safety. This quiz is available online at this page. Don't worry, this is NOT a "pass" or "fail" test! It's purpose is so you can find out what you really know about severe weather safety. If you fail the quiz, we also have a comprehensive safety page where you can learn more about safety. Their is a big difference between a severe weather "WATCH", and a severe weather "WARNING". Many folks still tend to get these terms confused with each other. The table below illustrates the difference between the two terms.
|TERM USED||WHAT IT MEANS||WHAT ACTIONS YOU SHOULD TAKE|
|Severe Thunderstorm WATCH||Atmospheric conditions are favorable for severe thunderstorm development over your area.||Continue on with normal activities. Keep watch on local weather developments. Be ready to respond to a warning. Monitor NOAA all hazards weather radio, or commercial radio and TV for further information.|
|Tornado WATCH||Atmospheric conditions are favorable for severe thunderstorm and tornado development over your area.||Continue on with normal activities. Keep watch on local weather developments. Be ready to respond to a warning. Monitor NOAA all hazards weather radio, or commercial radio and TV for further information.|
|Severe Thunderstorm WARNING||Severe thunderstorms are imminent, or now occurring in your area.||Cease all outdoor activities at once, and move quickly inside your house, or other safe sturdy building. Inside, stay away from windows and doors. Unplug all electrical items before the storms arrive, and don't use the telephone during the storm. Keep a watchful eye for signs of rotation within the clouds, or for a possible funnel cloud. If you observe any of these, get to your basement or storm cellar at once! Severe thunderstorms can and occasionally do produce tornadoes.|
|Tornado WARNING||A tornado has been sighted by trained spotters, or is being indicated by Doppler radar in your area.||Move quickly to your basement, or underground storm cellar. If your home does not have a basement or cellar, move quickly to the lowest level of the building. Then seek cover in any "interior" small room or hallway. Closets or bathrooms make good choices. In mobile homes, get out and move to a safe sturdy shelter. Act quickly, as seconds count!|