An Air Carrier pilot reported encountering severe turbulence causing a temporary loss of control when the aircraft entered a thunderstorm not depicted on their weather radar.

Narrative

I was the First Officer (FO) and pilot monitoring (PM) of the flight ZZZ1 to ZZZ. Metar for ZZZ was 10 kt. 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 [affecting a large region of the country] moving to the east. The Captain briefed the FAs and passengers prior to departure; and at cruise altitude in smooth air stating 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 the Captain turned the seat belt sign back on; the Captain slowed to turbulence penetration speed; and made a 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 even farther south. 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 we could see over the top of the storms with city lights in the distance and stars above at 35000 ft. on an easterly heading. Suddenly we encountered a rising dark wall of weather. I warned the Captain immediately but it was too late and we were in the developing storm. The aircraft rolled and yawed violently kicking off the Autopilot. The Captain quickly regained control started hand flying and he yelled; I need lower now. I quickly responded and relayed severe turbulence and the need to descend immediately to ATC. We were cleared to 24000 ft. and I selected it with VS down initially 2000 ft. per min. However due to the updraft intensity the aircraft climbed approximately 600 ft. before we began a slow descent.I couldn't believe the aircraft took as long as it did to descend. The Captain was doing his best to keep the aircraft speed around the turbulence penetration speed. The Captain made smooth corrective inputs not to force the nose down to prevent overstressing the aircraft. Collectively we came to the conclusion that this event may have lasted for 3 to 5 minutes. It felt like 15 to 20 seconds at most. We were able to re-engage the autopilot reaching 24000 ft. I immediately notified company via ACARS; called the FAs. FA 1 reported FA 2 had hit his head on the door however did not need medical attention. FA 1 informed the Captain that the passengers were indeed seated and no injuries were reported at that time. The Captain called FA 2 again and he said he had a headache but medical assistance was not required. The remainder of the flight was uneventful and we landed safely at ZZZ.I've been in unforeseen moderate turbulence before for; however this wasn't even close. This was a rapidly rapidly developing storm cell and I had never experienced being caught in an updraft like that before. What's even more puzzling; is the radar depicted NOTHING. I was constantly shifting the radar tilt up and down to get a better picture. It indicated no precipitation or weather at all. I would like the company consider adding more features to our Jepp EFB; particularly the use of internet to provide a more accurate depiction of weather; turbulence and ATIS.