FloodZoneMap.org

This day, May 17th, will be remembered as one of the more unusual tornado days in southwest Pennsylvania. Although overall levels of instability were fairly low, enough of that parameter, plus shear, was concentrated in the 0 to 3 km layer to allow for the formation of low-topped supercells during the early to mid-afternoon hours. Interaction with a surface boundary allowed for tornadogenesis in a few of the storms as low-level streamwise vorticity was ingested into updrafts. Three of the tornad