A stability analysis of AVE-IV severe weather soundings

An investigation was made to determine whether the stability and vertical structure of an average severe storm sounding, consisting of both thermodynamic and wind vertical profiles, could be distinguished from an average lag sounding taken three to six hours prior to severe weather occurrence. The term "average" is defined here to indicate the arithmetic mean of a parameter, as a function of altitude, determined from a large number of available observations taken either close to severe weather occurrence, or else more than three hours before it occurs. The investigative computations were also done to help determine if a severe storm forecast scheme or index could possibly be used or developed.

The study presents these mean vertical profiles of thermodynamic and wind parameters as a function of severity of the weather, determined from manually digitized radar (MDR) categories observed during the National Aeronautics and Space Administration (NASA) Atmospheric Variability Experiment IV (AVE-IV) which took place on April 24-25, 1975. Profile differences and stability index differences are presented along with the development of the Johnson Lag Index (JLI) which is determined entirely upon environmental vertical parameter differences between conditions three hours prior to severe weather, and severe weather itself.

All of the stability indices tested were then used on a separate and independent data sample (AVE-SESAME-I) consisting of individual soundings taken during April 10-11, 1979. The AVE-SESAME-I data profiles are presented along with stability index computations for each. All of the stability indices tested appeared to do a reasonable job in indicating both the severe weather, as well as the non-severe weather environment. As a pre-severe weather lag (three to six hours) index, only the JLI appears to show promise as a potential forecast index. More testing of this index, however, is needed.