Clear Weather

Ingredients for the perfect storm

April 27th was the 4 year anniversary of the second major tornado outbreak to hit the eastern third of the United States in 2011. Tornadoes were reported from Mississippi, northern Florida, and Alabama all the way up into New York. Similar to the outbreak of April 16th, 2011, this one was expected to make for a very bad day. Even with all the improvements in forecasting and warning technology, more than 200 people died that day with over a thousand more injured.

As our understanding of the elements needed to produce tornadoes improves, our ability to give advanced warning long before the storms take shape improves as well. Meteorologists now know to look for high dew points near the surface, strong vertical wind shear (the change in wind speed and direction with height), and a strong storm system - both high up in the atmosphere and as a frontal boundary near the surface. These ingredients are the basics for the "perfect storm" scenario when it comes to predicting a tornado outbreak.

The computer models used to make weather forecasts have come a long way over the last several decades in their ability to pinpoint the regions in which these ingredients will appear and the time frame for when the storms will begin. The closer the day of the outbreak gets, the more meteorologists can narrow down that window for severe weather.

By the early morning hours of April 27th, 2011, National Weather Service offices across the Southeast were doing their best to alert the public of the dangers the impending system held. By afternoon, Particularly Dangerous Situation (PDS) Tornado Watches were issued for the geographic areas in the bull's eye of the forecast models. PDS Tornado Watches are worded for effect in the hopes that people will understand that long-lived, strong tornadoes will be possible.

Even with the time to prepare and get the message out to the population of the affected area, the casualty numbers were devastating. When the storms began developing and producing tornadoes, most of them were traveling at about 50 miles per hour, which is incredibly fast compared to the average 20 to 30 mile per hour storm speed. Many people apparently thought they had more time than they did to get to safety according to some post-storm studies.

Adding to the issue of the speed of the storms, as the damage mounted, electricity and radio towers were down causing difficult communication of new warnings. Many of the deaths occurred in mobile homes, which are notoriously unsafe in severe weather, and with EF4 and EF5 rated tornadoes, even well-built structures are vulnerable to obliteration. Plus, for some reason, some people still have the "it's not going to happen to me" mentality and don't take the warnings seriously. Scientists are perplexed by that third point.

Luckily, there is no outbreak like that one expected in our near future. In fact, with the exception of a garden variety thunderstorm embedded in the rain showers expected over the next few day, we're not expecting any noteworthy weather this week.

For more information on the April 27th, 2011 outbreak, click here, and for a list of the Storm Prediction Center storm reports for that day, click here.