As we embark on the month of May, it seems appropriate to mention that this month usually represents the wettest month, with an average rainfall (based on data from the Waco airport) of almost 4.5 inches. May also frequently represents the zenith of our severe storm season, which typically begins in mid to late February and ends rather quickly after May 31st. These two "peaks" are actually interrelated, as I will try to explain below.

Spring (March through May) is a transition between winter and summer. In early Spring, we're still very much under the influence of the polar jetstream, which usually controls the weather across much of the U.S. during winter. Upper air storms bring strong winds aloft and can produce severe storm outbreaks, but this potential is tempered by a limited supply of warm, moist air to fuel storms. The Gulf of Mexico stays warm all year, but the air over the water of the Gulf varies in temperature and humidity much more widely than does the water in the Gulf. That's because water in the world's oceans acts as a heat sink, trapping the heat (energy) from the sun much more readily than does the air just above the water. There are often intrusions of cold, dry air into the Gulf of Mexico during winter, which wipe-out the supply of warm, most air until the cold, dry air modifies and assumes the characteristic of the Gulf waters it overlies. This normally takes about three days.

As we progress through March and April, the effect of the polar jetstream only gradually diminishes, while the availability of warm, moist air from the Gulf gradually increases. May has been shown to be the month in which the latter becomes dominant and the former continues slowly waning. By the end of May or early June, the jetstream typically is so far north that it has little impact on Central Texas weather. Warm, moist air continues building up over the Gulf and over southern Texas in June, while we often transition to increasingly hot and dry conditions in Central Texas by the mid to latter part of June.

This year, we have already seen a lot of severe weather. It isn't clear whether the recent pace of severe weather will continue into May. If it does, we could see some very serious outbreaks of severe thunderstorms over the next four weeks or so. On the other hand, I have seen years where there was active severe weather until May, and then an early onset of summer-like weather that stifled severe storm development for much of the month. It's too early to know what lies ahead for our area this May, but it could be a very interesting period if summer doesn't arrive early. Time will tell!