Central Plains: 9/7

A radar image from 2:25 p.m. CDT showing a developing supercell and its surging outflow.

September 7th was an interesting severe weather setup across the central Plains.  It was fairly complex from the start, several days out, but even leading up to the night before, there were uncertainties with how it would play out. That morning, things were coming together and it appeared that there was the potential for a few intense supercells in southern Nebraska or far northern Kansas during the mid to late afternoon. I headed west to get into position and things started to get even more complicated. Few storm chases are black and white easy and this one was far from straight-forward. A broken line of poorly organized convection moved through the Grand Island area early in the afternoon. While initially unimpressive, it should be noted that the environment downstream of these storms contained 50 to 60 knots of 0-6km shear, while there was considerable 0-3km storm relative helicity in their wake.

Mesoanalysis showing considerable 0-3km SRH in the wake of a lone supercell around 2 p.m. CDT.

Although the computer models did not show any robust cells developing until after 4 or 5 p.m., the southern portion of the apparently disorganized storms began to better develop. A supercell was forming at the southern flank and while initially elevated, was able to better organize. This storm was dropping very large hail and began to leave a cold pool behind in south-central Nebraska. The first image in this post illustrates what was happening. This “premature” supercell was effectively pushing the severe threat further south into northern Kansas, despite an otherwise favorable environment further northwest. The outflow boundary is quite evident on radar, essentially along the Nebraska/Kansas border.

The lone supercell went on to produce a few brief gustnadoes, but as it moved into northeastern Kansas, quickly weakened within a relatively stable environment. The rest of the day was relatively quiet. Since I had to be back in Atlanta for work the next day, I did not hang back to wait on an increasingly conditional severe threat. With that said, a few marginal supercell thunderstorms did develop, but most were not until after dark as the environment had gradually recovered. This day was a unique chase of one storm developing prematurely and effectively ruining the environment. Models suggested that thunderstorms would rapidly develop in an undisturbed environment late in the afternoon and take advantage of that. Instead, one elevated supercell took over early on and by the time other storms were able to form, it was literally too little, too late.

Nonetheless, the chase finished with views of developing thunderstorms in the western distance, as viewed from the far northeastern corner of Kansas. This produced a picturesque scene with an approaching sunset.