Atmospheric Speed Bumps

Slow Down, Atmosphere! Slow Down!

The reason March has been relatively dry is because the upper flow (winds in the atmosphere at about 18,000 ft and higher) is almost too dynamic and fast. The spring storms we usually see this time of the year are being shoved east of I-35 and into Dixie. The jet stream is a kind of storm superhighway. If you look at the jet stream on a map of the United States on any given day you would see maybe one or two troughs sagging toward the equator and maybe one or two ridges bulging toward the north pole. The troughs bring cooler and sometimes stormy weather, the ridges bring warm quiet weather. The jet stream trough over the Pacific coast or American west is an indicator that a stormy day or two may be right around the corner. The jet stream helps generate well defined areas of low pressure in the high plains of Colorado and New Mexico. You can compare these surface lows to a drain in your bathtub. In fact it would make even more sense if the drain was in the center of your bathtub to make this comparison. Lets say that on there's cooler water on the north end of your bathtub and warmer water on the south side of your bathtub. You open the drain and all the water begins to flow toward it. Science has shown that the most efficient way for gases and fluids to travel vertically is to spin in a vortex, thus the swirl of water around the drain (which, by the way, has nothing to do with what side of the equator you're on).
This is what a surface low (the red "L" on a weather map )does. It draws in warm air from the south and cold air from the north and dry air from the southwest and humid air from the Gulf of Mexico. As the air masses converge toward the center of low pressure they're deflected to the right and, on a very large scale, begin to spin around the low pressure much like the water around the bathtub drain. The leading edge of the warm humid air is drawn on a surface map as a warm front. The leading edge of the cooler air from the north is drawn as a cold front. And the dividing line between the moist gulf air and the dry desert air is drawn as the dryline. The dryline and the warm front will be the most likely places for stormy weather to develop, especially in the late afternoon. Oh, and instead of the air falling to the earth when it reaches the "drain" or the surface low, its actually drawn upward into the higher levels of the atmosphere. Now these surface features trigger storms only if they draw up enough moisture from the gulf to work with. For the the last 3-4 weeks these springtime scenarios have been sweeping through so quickly, they haven't stuck around long enough to draw in the moisture. The result, we see a lot of cold fronts and drylines sweep through with nary a cloud in sight. Once the atmosphere settles down, those stormy events this land has become known for will make us feel right at home.

JC