ProbSevere Ingredient Distributions

Many of the NWS forecasters appreciated seeing ProbSevere 1-d and 2-d distributions of the data fields used to calculate probabilities.   Forecasters wanted to see these because they wanted to understand why ProbTor values may be higher one day versus lower the next.  Or why one day may have more 90%+ ProbHail values versus another.

One topic discussed was a 2-d NWP-based predictor in ProbHail (figure below).  The red box indicates a very favorable environment for severe hail (ratios near 10, which act to increase ProbHail values, representative of OUN/SJT CWAs on May 1, 2019) and the yellow box indicates a more marginal environment for severe hail (ratios near 1, which are neutral (do not significantly increase or decrease ProbHail values), representative of OUN/TSA CWAs on April 30, 2019).  This was one reason forecasters were seeing more 90%+ ProbHail values on May 1 compared to April 30, when similar values of MESH were observed.

Forecasters really appreciated seeing this level of detail as a mechanism to better understand ProbSevere and how to interpret and use probabilities from day to day.

ProbSevere-ProbHail 2-d predictor of hail cape (CAPE -10C to -30C) vs precipitable water (PWAT).  The red box represented conditions in the OUN/SJT CWAs on May 1 2019 and the yellow box represents the conditions over OUN/TSA CWAs on April 30 2019.

-J. Sieglaff