This might explain that … the NEXRAD radar system was deployed in the 1990s. See here, NOAA 200th, with the salient part being this: “Based on the early work of the NSSL and JDOP, the national network of 150 WSR-88D (Weather Surveillance Radar- 1988 Doppler) radars, or NEXRAD (short for NEXt generation RADar) were deployed in the early to mid-1990s. The NEXRAD project replaced the older WSR-57 radars and now provides comprehensive radar coverage of the United States.”
According to this site (http://www.srh.noaa.gov/ohx/newsletter/120103.htm) the Nashville NEXRAD was commissioned in 1995, so that could explain the “increase” in tornado activity – better detection methods were in place.
gonzomax, your concern for the planet is noted, and it is a good thing. However, you seem to be confusing CO2 with pollution. Every dollar spent on regulating CO2 is a dollar that is not spent on the important issue, which as you point out is working to “clean the air and cut down emissions”.
My understanding is that NEXRAD allows for earlier, more precise location information, and better understanding of what’s going on inside clouds than Doppler does. Not, for example, coverage of areas which were previously unviewed by Doppler, so it would allow them to call things like tornado alerts earlier than before (since they’d be able to see the tornado forming, whereas before you’d only be able to spot them after they’d formed).
Which would explain the dramatic increase in F0 and F1 tornadoes, some of which don’t even reach the ground. They’re being reported as tornadoes when in the past they might have been considered just “really bad thunderstorms.”