KYKZ - Rob Robin Commentary

Well, here we are into the changing seasons once again, as spring begins first right down here on the gulf coast, then spreads progressively northward. Of course spring has both its good and its bad sides. The good side is the coming back to life of everything green, with its annual kaleidoscope of color making for a vivid contrast to the dull browns and grays of winter. The bad side of course is the ever-present threat of severe spring storms accompanying the passage of stronger Pacific systems through our area.

With the greening-up of everything, many people are starting spring gardens, even though the threat of late season freezes are certainly not out of the question. In a normal year severe true Arctic outbreaks become rare events after the middle of February (the temperature has never fallen into the teens after February 14th), although the latest freeze ever recorded here in Lake Charles is April 26th! The general rule of thumb is, after the middle of March most areas have seen their last freeze, according to the law of averages. With that general yardstick in mind, you take whatever degree of risk you choose in planting your spring garden early.

Of course our greatest concern this time of year is our springtime severe thunderstorm-tornado season, which begins the second half of February and peaks out during March and April, then drops off gradually during the month of May. Normally this begins along the gulf coast, then spreads northward with the change of seasons, reaching its maximum intensity in May across "tornado alley" in North Texas, Oklahoma, Kansas, & Missouri, and then advances northward into the central and northern plains in June and July, while slowly diminishing in intensity. Again this is just a very general rule of thumb, because there have been significant tornado outbreaks in the northern plains in early spring, as well as in late spring down south.

Fortunately for us down here on the gulf coast, the most ideal dynamics, clashes in differing airmasses, and peak of the strongest part of the season occurs up to our north, where the most intense tornadoes in the world are born out of rotating super-cell thunderstorms, creating their own private self-contained low pressure circulations that can travel hundreds of miles without dying out like a normal thunderstorm cell would. Besides carrying an auxiliary arsenal of large hail, damaging straight-line winds, and unreal lightning, these monsters can produce a whole series of tornadoes along their lengthy paths. Supported by sheering winds (winds that change from south to west with height), sharply contrasting airmasses in both humidity and temperature, and jet stream dynamics that favor a super lift once the thunderhead reaches the upper levels, tornado wind speeds of 200 to 300 miles per hour can be reached. Fortunately, these are conditions that are rarely seen down here on the gulf coast. Some prime examples of the strongest F-5 type long-track super-tornado are shown below. On the left is the 318-mph Oklahoma City monster of May 3^rd 1999, as it approached the suburb of Moore, briefly supporting two vortexes. On the right is the Wichita-Andover tornado of April 26^th 1991 as it tore through Mc Connell Air Force Base.

Locally, our most damaging spring severe weather outbreaks come with southern tracking Pacific storms, characterized by a deep stiff flow of rich tropical air off the gulf, with an advance guard of isolated super-cell thunderstorms running out ahead of the main cold front, and its squall line. The tornadoes with these are usually shorter lived and not as powerful as the super tornadoes up north, although the strongest can still easily demolish most structures. However, much of the wind damage in these storms is oftentimes caused by "straight line winds," a function of the cold downdraft and outflow coming out along the leading edge of the precipitation shaft, and these can reach hurricane force in a matter of seconds after the initial onset. The most severe form of this phenomenon is sometimes referred to as a "downburst." This powerful wind-blast is probably the single most underestimated factor in severe spring storms around here, and oftentimes these are reported in as tornadoes. People always state that they "heard a loud roar," which of course makes perfect sense. Hurricane force winds blowing through trees, power lines and various other obstacles on the ground will indeed produce a distinct roaring sound. Wind speeds can exceed 100 mph. A close-up inspection is oftentimes required following the storm to correctly identify the culprit.

If you are caught outside as one of these downbursts is approaching, you will sometimes observe a threatening rolling low cloud coming out on the immediate leading edge of the storm. These too are oftentimes phoned in as tornadoes. However, this cloud is caused by the cold air dropping down along the leading edge of the precipitation shaft, which then helps lift the warm moist air up ahead of it, like a plow. When this warm moist air contacts the colder air, it condenses, and you can then actually see the warm air lifting up, and the cold air sinking down, producing this very turbulent rolling cloud......but this cloud is rotating about a horizontal axis, while a tornado rotates about a vertical axis. I drew the chart below to illustrate the difference in the wind-flow between the two, and then inserted the two excellent pictures of a severe squall line that follow. Whichever is the case, whenever you see either a funnel cloud or roll cloud, the wise thing to do is to seek safe shelter immediately.

On the subject of sheltering, the one place you do not want to be in this type of situation is in a mobile home. Many people tend to think that tornadoes seek out mobile homes, since it seems like they are always targets of these storms. However the fact is, it takes a lot stronger wind to destroy a regular house than it does a mobile home, and some of our local tornadoes, and squall lines packing straight line winds which may not be strong enough to totally demolish a house, will roll a mobile home. This brings up the subject of "tie downs." Although these will not help in the case of strong tornadoes, they may well mean the difference between saving your home and having it rolled in the many somewhat less severe storms. In any event, be sure to have some safe place planned out in advance where you can go in these situations.

In a regular home, our frequently repeated advice to seek shelter somewhere in the middle of the house in a small room (like a closet or bathroom) with no outside facing walls still holds true, since we do not have basements down here. Forget opening windows to equalize the pressure, because it is the wind rotating around the outside part of the tornado that gets you. The real pressure drop is on the inside calm part of the funnel.

If caught outside, seek shelter in a ditch or culvert, as the wind will blow over the top of a depression. If in a car and out in open spaces, well away from the tornado, drive at right angles to its path. In other words, if it is coming at you from the southwest, move southeast or northwest to side-step it. However, if it is near you, get out of your car and do as we described earlier, as cars are rolled and tossed about like dice by tornadoes. If in doubt as to its distance, evacuate your vehicle, and remember, a tornado that appears to be standing still is probably either coming directly towards you, or headed directly away from you.

Other dangerous weapons in a severe spring storm's arsenal include hail and lightning. Hail larger than golf balls is uncommon, but not unheard of down this far south, and certainly can cause damage or injury. However, probably the most underestimated danger is cloud-to-ground lightning. Lightning is responsible for more fatalities each year in this country than the combined totals of both tornadoes and hurricanes put together. I will have a very detailed report on lightning coming up for thermal thunderstorm season this summer when far more people are out and about, and consequently struck by lightning. However, to briefly summarize some safety tips here........

Remember, lightning is basically high voltage static electricity, and will seek the shortest easiest path to ground. Air is a very poor conductor of electricity, and thus heats up explosively when forced to conduct it. Anything like a ground-wire leading down the side of a telephone pole, a flagpole, a tree, or anything wet or metal, is an easier conductor to ground. The rule of thumb is to stay away from these objects, or anything connected to them. As an example, when a lightning bolt strikes a telephone pole, even though the vast majority of the charge will be conducted to ground through lightning protection devices (such as lightning arresters and ground wires running down the pole), everything electric in your home is connected to that pole, and at such high voltages, tremendous field charges are oftentimes built up that cannot be dissipated by those safety devices, and people are sometimes electrocuted by using telephones or other electrical appliances during storms, caused by incidental power surges stemming from the main bolt.

Many people are killed by lightning through being connected to something else that actually sustains the main bolt, or they are at the very least injured, sometimes for life by the experience. I will have much more to say about lightning safety this summer. In the interim remember, stay away from high exposed objects or conductibles connected to them, and do not let yourself be a high exposed object.

Well, that just about wraps it up for this time. Thanks again for your continued support, and I invite you to look for future updates coming to this commentary page, which I will as usual, announce during my regular weathercasts.