March's 18 reported tornadoes was the fewest we have seen reported since 1978. April's tally of 78 is half of the national long-term average of 155 and continues the trend of below average intensity severe weather that started up last May.
The 2013 tally is 42 percent of the annual trend from 2005-2011 nationally, which includes 2011's rather robust severe weather tally as well as 2008, which was the other major severe weather season we've seen in recent times.
One of the causes of this year's less robust severe weather season has been the cold weather that dominated the Midwest and Plains. The jet stream's positioning has been less ideal for severe weather development this year. Unlike last year, where drought dominated the picture in the Midwest and Plains from May on, the pattern this year has been one of delayed Spring and a continuation of late winter in much of the Plains and Midwest on the whole. Temperatures have been significantly below average in much of the prime "Tornado Alley" real estate this month. This, combined with the jet stream generally aligned farther south and east than usual in the Plains and Midwest, has limited the levels of severe weather developing.
May and June are also significant severe weather months nationally so the lull in severe weather seen so far may very well come to a quick end in the coming weeks, dependent on storm system developments over the Plains and Midwest should those take place in May. However, with the two year anniversary of the Alabama tornado outbreak having just past, the lull in severe weather this year is welcome for many who are still recovering in the South.