Air carrier First Officer reported temporary loss of control due to unexpected severe turbulence.

Narrative

I was operating as the First Officer on a flight from MSY to ZZZ when we experienced severe turbulence around XA:00 at flight level 350. The Captain and I were developing a plan to maneuver around storm cells that were on our route. After careful consideration of ATC; dispatch; the aircraft weather radar; FD (Flight Deck) pro radar and WSI (Weather App); we created a course of action that kept us away from the storm cells. About 20 minutes into our new course of action conditions quickly deteriorated and the Captain told the flight attendants to immediately take their jump seats. Not too long after we experienced severe turbulence where we lost around 500 feet in altitude. The severe turbulence lasted about 3 to 5 seconds and then we were out of it in clear skies. The Captain recovered the plane; asked if I was all right and then talked to the flight attendant to get a report on the condition of themselves and the passengers. We got an okay from the flight attendants that there were no injuries and everyone was all right; and I reported to ATC of encountering severe turbulence. For the remainder of the flight; everything was smooth and clear of turbulence. The Captain and I debrief the situation and talked about even with all the tools we have it can be hard to predict where turbulence can occur; and it is best to create a large buffer from you and the storm cells.