Not a lot has changed since my blog on Friday, but at least now we are not totally reliant on computer models and can start looking at some real data, as the main upper low that is causing all this trouble has opened up and moved into AZ and NM, and will move into TX this morning.
Weather balloon data and surface observations already indicate pressures falling out ahead of this trough due to divergence aloft, and as the pressures fall from west to east, this produces south to southeast low-level flow, that is starting to come off the Gulf of Mexico. Dewpoints are above 60 now roughly north of a line from Mobile to Shreveport to Wichita Falls, TX.
As this warm, moist air pushes north as a warm front this morning, this will create lift in the atmosphere, and clouds and showers will spread across Alabama by 8 am. These are already occurring to our NW. A few thunderstorms have blown up over Oklahoma.
As the low-level flow off the Gulf intensifies by afternoon, the warm front will move northward through Alabama. As noted by the local NWS and by SPC, this is a complicated pattern. In addition, we are missing hundreds of atmospheric observations that normally flow into our weather analyses from commercial airliners that are not flying right now, so the forecast has more uncertainty than normal. The warm front will likely reach I-20 by around 1 pm, and the Tennessee border by 4 pm. This warm front could be a focus for some of the earliest severe storms, as wind shear is greatly enhanced along warm fronts. And, behind the front, the air mass will become steadily more unstable with time. Any sunshine will increase the instability, but it is doubtful that we get too many breaks in the clouds tomorrow.
In the image above, the HRRR model, a high-resolution model that is initializing well with what is actually happening in TX/LA right now, the CAPE at 7 pm tomorrow in the BHM area would be a healthy (but not extreme) 864 J/kg, and the helicity, or wind shear for storm rotation, a significant 482 m2/s2. This will provide the energy for some supercell thunderstorms, capable of producing significant tornadoes, across north and central Alabama between 2 pm and 9 pm. In the model-predicted map of helicity below, note the maximum along the warm front in northern AL.
Storms will likely grow into a squall line by 10 pm CDT, decreasing the tornado threat and increasing the tornado threat.
A lot of people all over Facebook and other social media have become meteorologists lately. Check their credentials…if they have no formal meteorology training and experience, consider the source. I can’t drive a fork lift, design a bridge, or put the pipes in a house; generally, fork lift drivers, civil engineers, and plumbers don’t make the best weather forecasters. Secondly, with the high-resolution of our computer models today, some very high severe weather parameters will naturally pop out in some localized areas. If you are as afraid as some of the people posting and commenting on social media seem to be, go ahead this morning and drive to south Georgia, as if you were evacuating a hurricane.
For the rest of us, yes, this is the most significant potential for severe weather I have seen in 3 years or so. There will likely be tornadoes. Large hail, damaging winds, and lightning will also occur. But this is not going to be like April 27, 2011. Still, if it hits your house, it will be awful. It’s Easter Sunday, and we’re in the middle of a quarantine for a virus. Please have at least two sources of weather information with you at all times. A good phone app that will alert you of tornado warnings where you are, and a properly programmed NOAA weather radio. Make sure your phone is charged and you have batteries for your radio. Also, flashlights, helmets, etc. Just stay calm, and will we get through this.
For additional safety information, see the end of my previous blog, at https://ckweather.com/2020/04/10/tornado-analysis-for-sunday/.
UAH will be conducting “limited” (because of COVID-19) severe weather operations tomorrow across the northern half of Alabama, with Doppler wind lidars, multiple Doppler radars, wind profilers, and weather balloons all over the place. My job will be to watch radar and their GPS locations and direct them to the right locations and, most importantly, keep everyone safe.
Dr. Tim Coleman