Forecasting Hail

[Jennifer Palmer]

I did a search and I couldn't find a previous thread on this subject, so I apologize if this has been covered before.

This morning I was checking out SPC and read the following text:

FORECAST SOUNDINGS STRONGLY SUGGEST SIGNIFICANT HAIL IN EXCESS OF 2 INCHES MAY BE NOTED WITH THESE SUPERCELL STRUCTURES.

I think I know how to "see" hail in a sounding, but after doing a little reading, maybe I don't know how to after all.

I know high CAPE is a good indicator that large hail will occur, but I know there has to be more to it than that.

Any help in this area is appreciated!

Thank you!

 

[jaredleighton]

You're on the right track in the sense that CAPE is needed for large hail formation, but it goes a little deeper than that. Soundings are good at showing where the steep low and mid level lapse rates are located in the atmospheric column...but first, obviously, you need to have a storm. All the CAPE in the world isn't worth much if you can't tap into that energy. For example lots of CAPE can be located above a low or mid level temperature inversion and will largely go unrealized unless a parcel of air can be lifted into that area of instability. Likewise, even uninhibited surface based instability can go unrealized if there is no trigger mechanism to initiate storms. Soundings also give a good idea about the amount of wind shear (both speed and directional), and shear is necessary to give strong updrafts an opportunity to persist for a long amount of time. In order for large hail to form it has to reside in the updraft long enough to coalesce, and if the updraft doesn't last longer than just a few minutes, then the hail has no real chance to gain size. One more important ingredient for large hail, with respect to the sounding, is having a lot of CAPE in the Hail Growth Zone, which resides in the -10 to -30 C layer of the atmosphere.

The WDTB has a lot of helpful modules regarding severe storms forecasting. These are the modules that forecasters for the NWS offices go through before taking on any warning responsibilities. This module on large hail forecasting is very helpful.

Hope this helps,

Jared

 

[Jennifer Palmer]

Thanks, Jared! This does help!