We saw heavy rain and storms on Saturday, then a big line of storms Monday night that knocked down some trees, and caused some hail. Most of us have seen around 3" of rain since Friday night. We are in a very active weather pattern, and another round of storms will move in tomorrow. Some of those storms may be intense, especially over west Alabama, with the possibility of lightning, damaging winds, and maybe even a few tornadoes.
Right now, an area of storms extends from southwest Louisiana up into Arkansas. Given the wind shear, SPC has placed parts of Louisiana, Arkansas, and western Mississippi under a tornado watch.
A closed upper low, much like we had on Saturday, will be to our northwest tomorrow. These closed upper lows are notoriously difficult to predict, especially in terms of the details of energy rotating around them, so this forecast has lower confidence than we had on Monday about the storms Monday night.
Notice, though, that the 850 mb winds (around 5,000 feet) are strongest to our northwest tomorrow, and this is usually where the strongest storms are located. We do not know how late into the night the area of thunderstorms to our southwest will last, and if it is still going on tomorrow morning, that could cut off our moisture supply somewhat for storms during the day. Part of the uncertainty. It does appear that, with even a little sunshine, temperatures will rise into the mid 70s, and dewpoint will go into the 60s. So, the air will be unstable enough for thunderstorm development, with CAPE around 1000 J/kg. However, with the low-level jet to our northwest, it looks like the wind shear will lessen as the system approaches central Alabama, and helicity values (shear that can produce storm rotation) will only be 100-200 m2/s2 here tomorrow. The energy-helicity index, that is a good measure of tornado potential, will only be 1 to 2 tomorrow over central Alabama. That is sufficient for a couple of tornadoes, but not a widespread tornado outbreak. 1 is usually the minimum for any tornadoes, and outbreaks of big tornadoes occur with values of 3 or more. In big outbreaks it is usually above 5.
We will have a chance of thunderstorms just about anytime tomorrow, with warm, moist air in place. As wind shear increases after 10 am, a few storms could be severe, and even a couple of tornadoes are possible. A cool front will move through tomorrow evening, probably bringing another line of thunderstorms, with the potential for damaging winds. But, this does not look like a major tornado event for Alabama. Maybe for Memphis or Tupelo, but probably not us. There is more uncertainty with this system due to the closed upper low like on Saturday (we thought there may be severe weather and there was just rain), and this time it could be worse than it looks. So, stay weather aware tomorrow and we will keep an eye on it for you!
Dr. Tim Coleman