Obstacle flow signature
From Glossary of Meteorology
obstacle flow signature
The Doppler velocity signature of middle-altitude flow around the strong updraft region of a severe thunderstorm. The signature indicates stronger flow around the edges of the updraft region and weaker (or reversed) flow in the wake region immediately downwind.
Though present for all radar viewing directions, it is most pronounced when a significant component of storm motion is toward or away from the radar.