We have mentioned in several previous blog posts that we were watching a storm rolling in from the Pacific that could make things interesting around these parts late this weekend. The models and their ensembles are in very good agreement on the evolution of the large-scale pattern. Thus, we have enough confidence to say that a significant regional severe weather episode, which includes the potential for damaging winds and tornadoes, is more likely than not either Sunday afternoon or night.
A strong middle and upper atmospheric storm system in the Southwestern United States Thursday afternoon is forecast to reach Texas by Saturday night. Meanwhile, another trough within the polar westerlies over the Gulf of Alaska will move eastward into the Northern High Plains at the same time. These two troughs are expected to merge (we call this "phasing") on Sunday, which will create a large and very powerful deep-layer trough that will begin marching toward the Central and Eastern United States. At the earth's surface, an area of low pressure will organize slowly at first over eastern Texas Saturday evening before intensifying more rapidly on its way to the southern Great Lakes states Sunday evening. An increasingly warm, moist and modestly unstable airmass will push into the deep south on the heels of strengthening southerly winds on Sunday. The large-scale lift associated with the powerful trough will overspread the unstable air creating an environment conducive for thunderstorm development. The strong tropospheric wind fields are expected to lead to extreme vertical wind shear. Supercells should be able to develop in that sort of environment.
Very early indications suggest a squall line will start organizing in eastern Texas Saturday evening, then translate eastward along the Gulf coast states on Sunday. The timing brings the line into our area late Sunday afternoon or evening. We are not yet certain whether either individual storm cells will be able to develop ahead of the line, or which parts of our area will have the highest severe weather threat. As those details become clearer, we will post additional information. We just wanted to give the "heads up" for now.