Due to a shift in how far inland warm air will get during the morning hours on Wednesday, the Storm Prediction Center has increased the risk for severe weather across South Mississippi.
There is a Slight Risk for closer to the Gulf Coast for Mississippi and Alabama.
From the SPC
Here is midnight discussion from the Storm Prediction Center:
Late-evening water-vapor imagery depicts a low-latitude short-wave trough over far west TX/northern Mexico digging east-southeast toward the TX coast. Thunderstorms have recently developed ahead of this feature in response to large-scale forcing for ascent that is spreading across south-central TX. Latest guidance suggest strong mid-level height falls will develop across the central Gulf States ahead of this feature which should encourage a weak surface low to evolve along associated cold front over the lower MS Valley early in the period. Boundary-layer moisture is not particularly high across the central Gulf coast but should increase during the morning hours with mid 60s possible prior to frontal passage. Latest thinking is a forced line of storms should evolve along the wind shift by mid-late morning then advance east ahead of the progressive trough.
Strengthening shear profiles will favor sustained organized squall line that should advance toward the FL Panhandle by late afternoon. While storm mode should be primarily linear, a few supercells could evolve immediately ahead of the line, or embedded within the frontal convection. Locally damaging winds are the primary threat but one or two tornadoes could develop near the coast. During the overnight hours, low-level trajectories will become more favorable for somewhat higher theta-e air mass to return to the FL Peninsula. This air mass recovery will prove favorable for continuation of frontal squall line and attendant severe threat with strongly sheared convection.
Karrie Meter
Timing
This will likely be a pretty quick event. Storms could start as early as 9am. Linger as late as 2pm.
Right now, it looks like the front will cross I-55 around 8am. As the atmosphere destabilizes by 10am, thunderstorms may develop along the I-59 corridor, moving east. By noon, storms will near a south-north line from Wiggins to Waynesboro, still moving east. By 2pm some of those storms will reach the Mississippi-Alabama border.
Science!
All aboard! And buckle up!
So, what changed?
Well there looks to be a decent push of warmer air at the lower levels of the atmosphere as this front progresses to the east. As stated by the SPC above, a surface area of low presure may develop and aid in pulling more warmer air up from the Gulf of Mexico. Simultaneously, the pooling of warmer air also means more moisture at the surface.
As the surface low develops, the orientation of the front will change to more of a SW-to-NE line. As it does so, the flow along the front at the surface up to about 4,000ft will align… Then flip back to the southwest pretty quickly above that point.
This is highlighted in the hodograph of the sounding information pulled from Pivotal Weather.
Notice the hodograph has a sickle-like shape, but that it isn’t complete. That is good news for keeping the tornado threat in -relative – check. Because winds get a bit wavy aloft, that should help to keep the threat for multiple supercells from getting too developed.
The stats pulled from the near-storm environment aren’t overly impressive. Though, they aren’t anything to sneeze at, either. CAPE may only be around 500, but shear, helicity, SigTor, LCL and 0-3km lapse rates are within the range to bring the area severe weather. And as we’ve learned over the years, it doesn’t take much to get severe weather in South Mississippi.
The Good News?
Two good things on the data above for keeping severe weather in check are the “ConvT” and “DCAPE” numbers.
The ConvT is the convective temperature. Generally, a good way to think of this is ‘how warm does it need to get in order to get storms going?’ and that is telling us 71 degrees.
Forecast high is only 65 tomorrow. That means we may never even get storms off the ground because it may never get quite warm enough.
The other number, the DCAPE, is the Downdraft CAPE. That is a measure of how much buoyancy a downdraft has. I know, I now… What does that even mean, Nick!? Don’t worry about what that means, just know that if we don’t get a number above 500, it gets difficult for tornadoes to form in our area. Not impossible, but more difficult.
So, despite all of the other numbers looking okay. The fact that those two numbers aren’t exactly lining up with what we would “need” that may limit our ability a bit to get a true severe weather threat up and going tomorrow.
The Bad News?
It might not matter. With the storms moving through at midday, the sun may be enough to overcome any lower numbers by adding extra heat to the equation.
Plus, if there is one thing that storms in the south can do – it is overcome low numbers. The tornado in alabama just a few days ago was in a place where all of the numbers were much lower than tornado-producing-history would suggest.
