So far, this multi-tiered storm outbreak had killed at least 15 people through Mississippi and Georgia - and my fear is that in the next 24 hours, there will be more names added to this list, especially after taking a look at the latest Storm Prediction Center (SPC) forecast, which rarely ever highlights regions of "Moderate" potential for severe weather, not to mention "High".
The significance of the terms "Moderate" and "High" in an SPC Outlook is that it shows extremely high confidence in extraordinarily dangerous weather occurring in a particular location. Really, only in historically significant, near-record tornadic outbreaks do you see a forecast of "High" probability for severe weather.
For instance, if you look above at the Tornado Forecast - You can see a black-hatched area through the "15%" and "30%" chance of tornadoes - indicating that not only is there a 15-30% chance of a tornado within 25 miles of any given point within the southern half of Georgia, the Northern half of Florida, and the Eastern half of South Carolina, there is at least a 10% chance that tornadoes will at least contain the strength of an EF-2 tornado - enough to be extremely destructive.
Looking at the Damaging Wind Forecast, we also notice a black-hatched area, indicating at least a 10% chance of winds in excess of 75 mph - which, in reality, can be be more widespread-destructive than tornadoes. When I see this, I immediately think of a Derecho - which is a line of very powerful thunderstorms - often containing tornadoes and large hail - that also moves at very fast speeds and have been known to cause winds in excess of 100 mph in isolated gusts.
Let's just say...it would be difficult for the Storm Prediction Center to draw anything more dangerous today.
So what makes the Storm Prediction Center so confident in a widespread severe weather outbreak?
Perhaps part of it has to do with the past couple of days of severe weather across the Gulf States. In the Science of Meteorology, understanding the past is key to forecasting the future (it's kind of like having the answer key in front of you, but with some of the pages missing).
What has me concerned? Well, I can't speak for the Storm Prediction Center, but just a quick glance at the atmospheric conditions both at the surface and aloft certainly sheds some light in their forecast.
For example, Dew Point Temperatures over 70 degrees through the Eastern Gulf (yellow), and over 60 degrees through Southern Alabama and Georgia (light yellow) means that there is an excessive amount of moisture available for significant thunderstorm development (and heavy rainfall leading to flooding concerns). A large amount of atmospheric instability is also needed, and we see that just ahead of the very distinct cold front seen below through Alabama and well into the Gulf of Mexico.
The Lifted Index above shows significant signs of atmospheric lapse rates far exceeding the atmospheric "normal", meaning that the low and mid-levels of the troposphere are cooling with altitude much faster than under normal circumstances. This opens a void of unstable air, which, in this case, is filled explosively with rich moisture and warm temperatures capable of severe thunderstorms.
Lastly, a quick look at mid-tropospheric vorticity, winds, and geopotential height above shows a prime environment for atmospheric lift and exhaust. In layman's terms, if the atmosphere wants to sustain severe weather, it must have a means of expelling spent energy while receiving a constant supply of new fuel. The vorticity image above not only shows a strong, negatively-tilted trough of Low Pressure (which brings significant atmospheric instability), but also strong, curving, divergent wind flow over Alabama, Georgia, and Florida, which allows for strong wind shear capable of tilting and rotating severe thunderstorms.