Tornado formation from downdraft interaction in the FACE mesonetwork.

Abstract

A tornado observed on 15 June 1973 in the FACE surface mesonetwork was studied on the mesoscale and cloud scale. Downdrafts from two preexisting cumulonimbi, initially 8Okm apart, met along a north-south line in the center of the mesonet 30min before tornado formation. Fed by the convergence of flow from the outflows of the predecessor cumulonimbi, a line of deep cumuli formed and developed rapidly. A tornado was observed as it dropped from this cumulus line. When the tornado dissipated 10 min later, heavy precipitation was reaching the surface and new outflow began to spread from the now vigorous cumulonimbus that had spawned the tornado. The life cycle of the tornado and a period of 90 min surrounding its occurrence are studied in detail from observed surface winds, radar reflectivity and surface rain gage data. -from Authors