Skew-Ts are an excellent source to gauge wind shear in the atmosphere.
Raw index numbers like bulk shear or helicity can be misleading when it comes to gauging how good the wind shear is.
Small problems with shear can make or break a day, from a weakness in the mid level jet stream winds to some slight backing of winds in the upper atmosphere.
But for today, let’s get an introduction on how to use Skew-Ts to gauge wind shear.
Wind Shear is Vitally Important
The environmental shear is incredibly important to storm mode and strength on a storm chase day.
Because of this, small problems with shear will create big problems for storms within an environment. There are multiple instances when a day almost became an outbreak but didn’t because of a slight problem with wind shear. One such day I can think of easily is May 30, 2013.
There are two things we tend to look for with shear to make or break chase days:
- Is there good turning? From the surface to about 850mb (or a couple thousand feet up) and also is there some turning from 850mb-500mb. Ideally you want quite a bit of turning in the low levels (45 degrees or so) with more gradual turning at 850-500mb (think SSW to SW). A lack of turning can create some messy storm modes typically. Also beware of winds that suddenly back then veer again with height. Good wind shear are winds that gradually turn westward with height.
- Are the speeds increasing with height? Wind speeds increasing with height is super important for updraft ventilation. If you have a major weakness above the surface, updrafts could tend to rain back into themselves or the rotation within the storm could be weakened.