You won't hear too many people complaining in the Midwest or the South about the lack of tornadic activity that we've had so far in 2013. But hey, there's no harm in pointing out some good news!
So far this year, about 250 tornadoes have been reported, according to the Storm Prediction Center. That may sound like a lot, but keep in mind that many of the tornadoes are relatively weak. For instance, we had 2 tornadoes in the DMV on April 19th, but the damage was limited to the superficial structure of buildings and homes (roofs, siding, windows and doors). The power behind these twisters was far lacking in comparison to the violent F4 tornado that devastated LaPlata, MD in 2002. That tornado completely leveled buildings and, tragically, three people lost their lives.
The recent lack of strong tornadoes has also led to fewer tornado deaths. I'm sure you remember the horrible scenes in Joplin, MO and Tuscaloosa, AL. Nearly 500 people died in those two tornado outbreaks alone; both happened in 2011. This year so far, the number of fatalities is in the single digits. We never want to see anyone lose their life in one of these storms, but obviously this number is astoundingly low in comparison to what we had just 2 years ago in the Midwest and the South.
This trend in lowered tornado numbers began last year. As a matter of fact, the period from May 2012 until April 2013 has been the least-deadly in relation to tornadoes in the USA's recorded history!
It's possible that the lower number of tornadoes is partly due to a lower amount of ice in the Arctic Circle. In September 2012, the Arctic sea ice extent was the lowest it's ever been since measurements were first taken, according to the National Snow& Ice Data Center. The sea ice obviously helps to keep the air colder right above the ice. Why is this relevant? Because the power of the jet stream is largely driven by the contrast in temperature between the Arctic and the tropics. If that temperature contrast is weaker due to a lack in sea ice, it could in turn make for a weaker jet stream. And since the jet stream provides much of the energy for tornadic activity, a weaker jet could be a leading cause for weaker tornadoes!
Of course, the severe weather season is just getting underway, and the pattern very well could flip as we head toward summer. But so far, this Spring has been fairly benign for most of the USA. It's bad news for storm chasers, but good news for just about everyone else!