A Bell helicopter pilot reported a loss of aircraft control due to a wind shear associated with a developing storm. The pilot was able to safely regain control; and return to base.

Narrative

Mission was training flight to a public relations event; the flight to the event was uneventful but we saw some weather to the south. As we were conducting briefings to the public we kept track of the now building thunder storm to the south; both visual and on internet radar. We determined the storm was growing more rabidly so we cut the event short. The departure plan was to hover behind two staged vehicles for a photo the hover away and make our takeoff run to the rear of the vehicles climbing out. All went as planned with the hover and reposition for departure; just about the time we was passing through ZZZ the aircraft encountered a wind sear of great strength causing the helicopter to both roll and yaw and dip down pushing us over the parked vehicles; applying corrective input and maximum power we flew out of the shear and had an uneventful return flight. The strength of the shear with a storm that was over 12 miles away was unexpected. With the rapid build up and the delay in internet weather display we should have returned earlier to avoid unpredictable storm effects.