Storms will form in the early afternoon near an upper and surface low and swing north/east around the low center into the evening. As a cold front crashes, more storms may form in Kansas and as far south as Northern Oklahoma. The tornado risk is low today, but it is centered in a small time/space area in Nebraska; let’s dive in.
Today’s low tornado risk is centered from Northern Kansas into Central Nebraska.
The culprit for today’s severe weather is an upper jet streak swinging around a robust upper low that will nose into the Central Plains this afternoon and tonight. This will help fuel plenty of wind shear for severe weather.
The stacked and deep nature of the low will mean strong 850mb flow will help increase low-level helicity values to the point where you can expect some tornadoes with deep surface convection.
Similarly, for at least a few hours this afternoon, dewpoints approaching 60Fough for robust will be good surface-based convection.
CAMs are initiating multiple storms near the low in Nebraska and more on the crashing cold front in Kansas. The storms in Kansas will be capable of hail and damaging winds, but the tornado risk is very low.
Looking at soundings near the low in Nebraska, the tornado risk will come down to the degree of surface heating. The 0-1km SRH values for a right-moving, cyclonic storm are impressive (400+ m2/s2). However, the surface temperature isn’t conducive to tornado formation on this, sounding ahead of a supercell on the HRRR. You can see this clearly in the -134 CINH values for the surface parcel.
The overall CAPE values are also pretty weak, which is probably why the HRRR doesn’t maintain robust updrafts into sunset. From the looks of things, the warm sector is very narrow.
This is a surface profile a bit earlier in the day. The shear numbers are less impressive overall, but the instability values support robust low-topped storms near the low. In this scenario, the tilting/stretching of what will likely be ample vorticity (spin) in the atmosphere may be enough for a storm or two to go off with a few tornadoes. Hail will also be a threat with these storms, but the sizes shouldn’t be too big.
The Bottom Line
It seems evident that there’s a small window for tornadoes across Central/Southern Nebraska this afternoon. From 1-4 p.m., I think there’s enough surface heating and shear to make a tornado threat real with any robust updrafts. However, these setups can be very finicky, so a few degrees less of surface heating or a slightly mistimed initiation could lead to storms maturing and running out of the instability axis before they can get down to business.
A low tornado threat is obvious, and that threat could seem pretty high on a local level if a storm can get going in Southern Nebraska.