Editor’s note: Stephen is a life-long Houstonian and avid weather-geek. He grew up fascinated with the wild Houston weather and loves writing about the processes that create it and its impacts on the area. You can find him on twitter @stephenuzick
By STEPHEN UZICK
Everyone knows that old saying “the only things certain in life are death and taxes.” But now I think we can add rain on tax day to those certainties. For the second year in a row heavy rain is falling on Tax Day. While this event is nowhere near the intensity or magnitude of last year’s flood it is definitely an interesting coincidence. Here is a very brief explanation of what is going on out there today.
Today’s rain is the result of both an area of low pressure in the middle levels of the atmosphere and the thunderstorms that low brought yesterday afternoon and evening. If you were caught in those storms you might have noticed a discernible drop in temperature and and humidity after they moved through. However that cooler air did not spread or linger across the whole area which resulted in pockets of differing temperature and humidity levels. The boundaries between those spots and the unaffected zones served as a focusing and triggering mechanisms for the storms today.
So what exactly are those boundaries doing? In effect they are acting like a ramp for moisture to rise into the atmosphere. As I have written about previously, cooler less humid air is more dense than warm moist air. When the warm moist air blowing in off the Gulf encounters those boundaries of cooler denser air, it is forced up and over those areas as it has a lower density and is more buoyant. That provides the rising motion necessary to create thunderstorms. Add to that the parent area of low pressure, also producing rising motion and pulling moisture in off the Gulf and you have the ingredients for storms today.