On March 30th, 2021, there was a unique atmospheric setup across parts of south Mississippi. This type of severe weather event doesn’t come along often, but when it does, it makes a very tricky situation for National weather service meteorologists.
Thankfully, for folks across south Mississippi, the crew of people who staff the local NWS offices are total pros. And while they can miss the occasional brief tornado… The fact we can say “miss an occasional brief tornado” is “as bad as it gets” is actually an incredible feat.
The tornado
This tornado formed just north of the Forrest / Covington county line and zipped north-northeast across Highway 49.
At the time, while it did exhibit some weak rotation, the thought was it was a “low topped supercell” and not capable of producing a tornado.
A BRIEF NOTE ON ‘LOW TOPPED SUPERCELLS’ FROM THE NWS:
-Members of the supercell spectrum of severe thunderstorms include 1) classic, 2) high precipitation (HP), and 3) low precipitation (LP). Classic supercells that typically occur over the Plains states have been well researched and documented, and often are large horizontally, tall vertically, contain deep mesocyclones (rotating updrafts), and frequently produce large hail, damaging winds, and occasionally weak to violent tornadoes.
-However, a number of supercells occur that are more diminutive both horizontally and vertically than the classic storms typical of the Plains. Nevertheless, these smaller storms often possess the same radar attributes, albeit sometimes more subtle, as their larger counterparts, including hook echoes, weak echo regions (WERs), bounded weak echo regions (BWERs) aloft, and mesocyclones. In essence, these storms are miniature versions of large, classic supercells and contain lower echo tops; thus, they have been called “mini supercells” or “low-topped supercells.” On radar, mini supercells can be isolated (similar to classic storms) or embedded within squall lines (similar to HP storms).
-Due to their diminutive horizontal and vertical size, proper mini supercell detection and assessment may be more difficult than for larger, deeper (classic) supercells. In addition, mini storm attributes will become more difficult to discern at long ranges, making knowledge of the storm environment and viewing of data from adjacent, closer radars very important.
-Due to the relatively small diameters of mini supercell mesocyclones, their radar-displayed strength (Vr values) may be lower than in reality due to velocity averaging in neighboring radar beams. This is a reason why apparent “minimal” or “moderate” mesocyclones are capable of producing tornadoes.
-In general, detection of mini supercells at ranges greater than 60 nm (110 km) may suffer from a slight loss of resolution (although still be viewable), while detections at ranges over 90 nm (170 km) may be more difficult in certain situations (Burgess et al. 1995).
Take a look at the threat by Daniel Lamb, the meteorologist on radar at the National Weather Service in Jackson that day:
For the next time
During events like this one, when storms may be riding a little boundary capable of brief spin-up tornadoes, it is all about identifying the boundary as soon as possible. At times “as soon as possible” may come after the first tornado is on the ground. Other times we will be able to pick it out in the satellite imagery.
For you, on day where a warm front is passing through the area and you get two rounds of storms – one in the morning and another in the afternoon – pay close attention to the storms in the afternoon. Those storms will have access to a bit more instability and may interact with any outflow boundaries laid down by the earlier showers and storms.
But also recognize that not every storm that produces a tornado will be easy to identify to get the warning out. There are limitations to what meteorologists can do – particularly in south Mississippi, due to a lack of full radar coverage.
This is why it is most important to keep an eye to the sky on days when severe weather is possible – even by the slimmest of margins! Because in south Mississippi situations like this can occur and tornadoes can form at a moment’s notice.
