So, Why Does Severe Weather Season Typically Peak In April/May Within The United States?

DISCUSSION: When it comes to trying to forecast or at least anticipate when there will be a larger threat for severe weather across the contiguous United States (or other parts of the Northern Hemisphere) during the Spring-time season, there is no question that there are most definitely times where concerns increase. More specifically, during the period from April to mid-June in the Northern Hemisphere and across a good portion of North America for that matter, there is often the greatest climatological threat for the development of larger-scale weather patterns which are conducive for the threat of severe weather events.

The reason for this increased severe weather threat is the fact that the period between April and mid-June is the period during which there is a bolstered contrast between cooler air masses (i.e., polar-originating air masses) and warmer air masses (i.e., sub-tropical/tropical-originating air masses). As a result of this increased propensity for air mass “clashes”, there is often a corresponding increase in the potential for increased atmospheric instability and severe storm potential. This severe storm potential increase is essentially a consequence of the atmosphere trying to restore a state of stability to what is a much more unstable low to mid-level atmospheric environmental set-up.

One such example of this concept is defined by the convective storm outburst which unfolded earlier in the day on Sunday (5 May 2019) in which strong to severe convective storms fired to the east of a developing low-pressure system. In this case, the dry-line feature which often is present during the Spring to Summer-time seasons across the South-Central Plains region, helped to generate deep convective storms which stretched from southwest Texas to eastern Nebraska with intermittent discontinuity between the areas of deepest convection in that stretch of the United States. In the simplest context, a dry-line is an arbitrary atmospheric boundary which separates hotter and drier desert air from warm, moist air which often originates from the Gulf of Mexico. To learn about what dry lines physically are, we welcome you to search the home page of our website for “dry line” since we have more details on that atmospheric topic with interactive graphics.

Thus, this example of real-life convective storms goes to show that the atmosphere is often capable of generating strong to severe storms under the correct environmental circumstances.

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© 2019 Meteorologist Jordan Rabinowitz