As this next system swings through the area, the front will fire up a round of thunderstorms. Those storms will slide through South Mississippi with a chance for heavy rain, frequent lightning, wind gusts exceeding 65mph, hail up to the size of quarters and the possibility for a tornado or two. Storms will move from west to east across the area between about 7am and about 2pm. So make sure you have your NOAA Weather Radio turned on and programmed correctly.
Guidance! Guidance! My Kingdom for some Guidance!
Model guidance continues to show a pretty stout system emerging from the Rockies as Friday turns to Saturday. The area of surface low pressure will ride from about Colorado Springs south to Oklahoma City and then back northeast past Memphis. Pulling with it a pretty sharp cold front.
The GFS, GFS-FV3, NAM, and NAM-3km computer weather models all show this is some form or fashion. The higher resolution model guidance, like the NAM and NAM-3km, bring the front through an hour or so later than the lower resolution GFS and GFS-FV3.
As the front passes, it will slide through an area where the atmosphere aloft will be conducive for the development of severe weather. Model data, across the board, shows plenty of wind shear aloft with cooler than normal temperatures, too.
The “cooler than normal temperatures” part is, in this case, almost as important as the wind shear. Because, in this specific case, the cooler air is going to increase the area’s instability in such a way that the surface temperature won’t need to be as warm in order to get storms and/or severe weather developed.
South Mississippi almost always has enough wind shear in the winter. But, generally, the area lacks instability with these winter events. Since model data is showing cooler than normal air moving in aloft, that increases the threat for stronger storms – even if all other things remain as they usually would.
The good news?
Historically, the CIPS Analogs isn’t impressed with a severe weather outbreak. It shows just a 20- to 40-percent chance that the area sees one severe storm.
Checking the tornado data, and it shows the percent chance that the area sees a tornado is down around 10-percent.
That means that of the Top 15 times the atmosphere looked like this in the past, only one or two times did we see a tornado develop.
But again, while the tornado threat might be lower, I think the straight-line wind will be our biggest concern with storms that move through tomorrow.
Just how severe are we talkin’ here?
Thankfully, nothing too crazy. We are still talking about a Slight Risk. Saturday isn’t expected to be a severe weather outbreak. In fact, for South Mississippi, only a handful of severe storms is the most likely scenario. While a tornado can’t be ruled out, that isn’t the main concern.
For South Mississippi, the biggest concern will be heavy rain and wind gusts up over 65mph. I still think hail up to the size of quarters is possible, but the more I look at the latest data, the less I’m convinced of such a threat.
The wind may really be cranking in some of these storms, though. I wouldn’t be surprised if it ‘feels’ like there is a tornado outside during a few of these thunderstorms given how gusty the wind may be. Aloft, we may have wind at 50 to 70mph up at 1500 feet. If that gets mixed down during a storm, that will hit the ground running and likely cause some damage to things like trees, roofs, and fences.
The 00z HREF Ensemble data show a swath of decent – but not crazy high – Updraft Helicity sweeps to the west of the area. Looking at the different HRW models, most slices of UH that move across South Mississippi are below 75m2/s2. Most are around 30 yp 40. And, in general, it is difficult to get a violent tornado (EF-4 / EF-5) with UH values at or below 75.
That said, a non-violent tornado can cause damage, too. So please take the threat seriously. In the past even EF-0 and EF-1 tornadoes have injured folks who were caught off-guard. The good news is that with the weaker tornadoes, so long as you are in your safe place and are protecting yourself, the chances that you make it through okay are very high.
From the Storm Prediction Center
Here is the Day 2 discussion from the SPC…
Ongoing storms across the Lower MS Valley Saturday morning are forecast to consolidate along the cold front into central MS by 18Z, and continue eastward into AL through afternoon. Large looping hodographs combined with sufficient instability will favor line segments, possibly QLCS in nature, or perhaps a supercell or two capable of a brief tornado. Damaging winds appear to be the primary threat across the Slight Risk area with 850 mb winds of 50-60 kt. By evening, as the front progresses into GA, the risk is expected to wane as instability becomes less, and large-scale lift shifts northeast of the area. Still, a few damaging wind gusts may occur into GA.
What should I do?
Treat this like any other severe weather day. There is a chance for strong to severe storms across the area, so act like it!
If you have outdoor plans in the morning or around lunch, you may want to change those plans. Or – at the very least – have a plan for what to do if a Severe Thunderstorm Warning or Tornado Warning is issued for your area. Have a NOAA Weather Radio or, again at the very least, an app on your phone that will alert you if a warning is issued for your area.
The main thing: We want to make sure you can get warning information from the National Weather Service.
The threat should end by about 2pm. Then much colder air starts to funnel into the area. But I’ll save that information for another post! Stay safe out there, friends!
