Flight Crew Air Transport Pilot (ATP)
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert; Flight Crew Regained Aircraft Control; Flight Crew FLC Overrode Automation; Flight Crew Returned To Clearance
Weather
Penetrating a line of thunderstorms through a large gap at FL330; painting no radar returns; radar adjusted to -2.0 degrees down; at approximately 10 miles range a small purple dot return appeared on radar. It was representative of a line of cloud that topped no more than FL350. We could see ahead as we were VMC at this time and we turned approx 20 degrees left and avoided the purple return by 3-5 miles best I can guess. Upon entering the smooth looking cloud; we hit severe turbulence which lifted us from FL330 to 34;300 ft within seconds and placed the jet into a 40-degree left bank. As altitude was still increasing and airspeed as well; with the trend arrow going well into the red barber pole for an over speed situation; I took command of the jet; turned the autopilot off and pitched the nose down to arrest the ascent. As I did this airspeed now went to the negative nearly entering an alpha floor situation. I hand flew the jet until aircraft control was regained. I then turned on the autopilot and gave aircraft control back to the FO (First Officer). ATC then queried us on our altitude deviation. No limitations appear to have been exceeded and on checking with the flight attendants there were no issues or injuries in the cabin.This was a one of a kind event in my [many] years of flying. All normal precautions were taken. Radar was being monitored and nothing unusual was being indicated until the small purple return; the size of a pen dot; appeared at about 10 miles away. We took action and missed the indicated return by 2-3 miles.
During our deviation; we clipped a 'benign/smooth-looking' cloud which generated severe turbulence. We gained approximately 1300 ft in what we estimate to be 3 seconds and were put into approximately a 40-degree bank to the left.
A320 Flight Crew reported severe turbulence after clipping a benign looking cloud.