Too much shear?

[Nick Dewhirst]

So back on March 14, 2019 southern Michigan had some very early tornadoes, one of which was a strong EF-2 west of Flint. There was a strong surface cyclone back near Nebraska/Iowa around 980 mbs or so with very strong southerly flow to its east. MLCAPE was marginal (around 300 J/Kg), but shear was off the charts.

On the afternoon sounding for DTX, 0-1 km bulk shear was clocked at 58 knots, and 0-6 km bulk shear was around 100 knots. Surface winds were from the south and winds around 6km were southwesterly. 0-3km SRH values approached 1000 m2/s2.

I’m really curious to whether there are ever cases where storms are just sheared apart by winds aloft, as I’m really surprised these weren’t. Although I have to say the winds aloft at different levels collectively were so strong they contributed to a very fast storm motion. A supercell ahead of the main line produced hail over an inch in diameter and raced north-northeast around 85 knots.

If anyone has ever seen a type of scenario where there’s “too much shear” I’d like to hear about it.

 

[Jeff Duda]

Look up the term "bulk Richardson number", especially as it applies to severe convective storms. You'll get more than you ever hoped for on the topic.

 

[Nick Dewhirst]

Thanks, Jeff! I've heard the term tossed here and there but never looked into it. Just checked it out through the AMS, and I didn't realize how important those values can be for forecasting.