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.