Time to Chase

Are you talking about the plains?

Typically, the main "chase season" is considered to start on the first of May. However, I find that there is at least one decent day in March, with April usually having a few good days as well. May will typically begin the major stuff, and will last through June (notabley this year, when some of the best setups of the year was in the first two weeks of June) and into July for NE/SD/MN.
March/April weather systems can be very dynamic with very strong kinematic fields/winds aloft. The instability is usually the make-or-break factor with these type of systems as the warm sector is prone to being socked in with crap clouds/convection (yes that's the technical term :D ) or the Gulf has recently been scoured and can only provide marginal to moderate dewpoints.

If the instability is not sufficient to sustain updrafts through the extreme shear, only the strong forcing right on the dryline can overcome the cap and the result is a huge, fast moving squall line that is usually not very photogenic but can produce widespread damaging winds/sometimes embedded tornadoes. Classic recent examples include April 6, 2001 and March 4, 2004.

If the instability is enough for sustained strong updrafts and T/Td spreads are small enough for sufficiently low cloud bases...watch out! There are many examples of infamous outbreaks of violent, killer tornadoes in April and sometimes March.

4/11/65 (IL, IN, OH)

4/3/74 (Super Outbreak, IN, OH, KY, TN, MS, AL, several others)

3/13/90 (OK, KS, NE, IA, IL)

4/26/91 (OK, KS, NE)

3/27/94 (AL, GA, SC)

4/19/96 (IL, IN)

4/8/98 (GA)

4/16/98 (TN)

4/8/99 (NE, IA, MO, IL, OH)

4/20/04 (IL, IN)

To name a few

Note: These situations may not be ideal for chasing because the extreme dynamics/wind fields make for fast moving storms.
In the lower Ms valley all the way to the gulf coast is very active in April. In March the good stuff is normally in E. Tx, La, Ar and Alabama. These areas are not good chase areas do to tall tree's, bad roads, storms are usually HP and moving pretty quickly in the early spring. In mid-late area there is usually one or two good chase days in the Ms delta area which is very flat with good roads. Like Nick said, the good stuff in the plains is usually from mid April through mid June.
Andrew, if you're talking about East TN (and most of the southeast) March through May is pretty much prime time. Unfortunately for chasers,much of the activity is nocturnal and squall lines. There is the rare supercell event, however; two that come to mind pretty quickly are May 15, 1997 (I think that's the right date; it might have been May 19) and April 16, 1998. Both events produced tornadic supercells in Middle and East TN. Of course the hilly, mountainous, tree-laden terrain plays havoc with chasing as far as visibility goes, not to mention lack of road options and most storms that you're dealing with in that area will be heavy rain producers, so you've got the possiblity of flash flooding to deal with also, as well as storms that move 40+mph. November and December are the area's "second season" as the jet stream migrates back north (November 10, 2002 sound familiar?) , as well as some December activity in Middle and West TN. There was a tornado outbreak in Middle and East TN February 21, 1993, 3 weeks before the "Superstorm" buried East TN under 2 feet of snow.
That's the long answer, I guess. The short answer would be yep, you can get severe in March and April. Mom Nature doesn't play by the calendar. If conditions are right, the storms will come.
April was tough for me in previous years, but it turned out to be the best month (sadly enough) for me..


April chasing isn't bad.. just be prepared to haul balls!
Andrew: Check out the severe climatology website with animated loops and graphics showing annual cycles, threat, etc at:

There are definite severe storms in April. Some years April is the best chase month in Texas. I believe the 1974 Super Outbreak occured in April. I intercepted the Hoisington F4 in April a few years ago. March can also be busy in TX in some years.

The cycle usually starts out early toward FL, GA, AL maybe as eary as Feb, or March, and then works into TX by April / May. Next it expands northward toward OK, KS, NE. Some of these events may include the Midwest, or over toward MO, IL, WI, etc later June / July typically take the pattern north toward SD, ND, MT, MN, IA, etc.
My two most-photogenic tornadoes of 2005 were in April:


F3 south of Galesburg, KS April 21


F1 south of South Mound, KS April 21

Normally April has been my nemesis, but despite the popular trend of recent, I never turned my back on her.