In yesterday’s forecast blog, we mentioned the lack of backed winds nearer the surface being a limiter to the overall tornado threat. In reality, a deadly tornado event impacted populated areas in Tennessee. In the image above you can compare the forecast hodograph with the one in reality. This is a bit more of an advanced post, but it’s worth talking about yesterday at this level.

If you want to learn more about hodographs to understand this recap, be sure to check out our Hodographs course on our website.

Higher-resolution models forecast a hodograph with a pronounced layer of backing in the 3-6km layer which led to a more linear mode with storms (top graphic). Additionally, this was combined with much lower than forecast instability to create a highly underdone environment. As we say models lie. And yesterday, they lied in a few small ways that made a huge difference.

The bottom graphic is the Nashville VWP just shortly before a tornadic supercell moved into town. On it, you can see the 3-6km layer is slightly backed but not as pronounced as models had said. This likely had a hand in helping maintain a dominant supercell storm mode longer in the presence of substantial 0-1km storm relative helicity. The slight backing in the 3-6km layer has been shown to be favorable for maintaining supercells for longer periods of time with more favorable storm motions.

The differences here are subtle but very important. There is much more to break down from this day — but even something as small as this can be the difference maker in reality vs. expectations. The weather can be very complicated after all.