EMB-175 Captain reported encountering severe turbulence; resulting in a momentary loss of aircraft control and an altitude deviation of 600 ft. After exiting the turbulent conditions; the flight continued to the destination airport; with only a minor injury sustained by a Flight Attendant.

Narrative

I was the Pilot in Command (PIC) and Pilot Flying (PF) of the flight ZZZ1 to ZZZ2. Metar for ZZZ2 was 10kt winds -RA Few036 BKN 050 and TAF called for 09005kt 6sm -shra sct025 ovc040. Multiple squall lines present associated with a cold front at departure time to the north; south and southeast of filed route effecting most of the southeast US and the gulf moving east. I briefed the Flight Attendants (FAs) and passengers prior to departure; and at cruise altitude in smooth air that we would be flying around weather in the near future in case someone wanted to use the facilities. Approximately 40-50 minutes left in flight time I turned the seat belt sign back on; slowed to turbulence penetration speed; and made the PA announcement for everyone to return to their seats as we were getting close to areas of known weather. The majority of the storms were in a mass about 50 miles north of our filed route with widely scattered storms to the south extending to the southern tip of the US. We requested deviations to the right of course (south) due to lightning along our filed route and up to 20 degrees was approved. Onboard weather radar showed a wide gap in the line of storms which we headed for and I could see over the top of the storms with city lights in the distance and stars above at level 350 on an easterly heading. Suddenly we encountered a rising dark wall of weather. The First Officer (FO) warned me immediately but it was too late and we were in the developing storm. The aircraft rolled and yawed violently kicking off the Autopilot (AP). I quickly regained control started hand flying and yelled I need lower now. The FO relayed severe turbulence and the need to descend immediately to ATC. We were cleared to FL 240 and the FO selected it with VS down. However due to the updraft intensity the aircraft climbed approximately 600 ft. before we began a slow descent. I was doing my best to keep the aircraft speed around the turbulence penetration speed so I did not force a pitch down to prevent overstressing the aircraft. Although I have been told the event may have lasted minutes it felt like 15-20 seconds at most. My FO immediately notified company via acars called the FAs. FA 1 reported FA 2 had hit their head on the door however did not need medical attention. FA 1 informed me the passengers were indeed seated and no injuries were reported at that time. I called FA 2 again and said they had a headache but medical assistance was not required. The remainder of the flight was uneventful and we landed safely at ZZZ2. Having access to real time weather radar via internet in this instance would have greatly supplemented onboard wx radar and enhanced situational awareness.