CRJ-900 pilot reported temporary loss of aircraft control while encountering severe turbulence during descent. Flight diverted and landed uneventfully.

Narrative

While flying from ZZZ1 to ZZZ on the ZZZZZ arrival; entered moderate to severe turbulence conditions accompanied by significant wind shear which caused the aircraft to struggle to maintain its cleared flight path. Approaching ZZZZZ intersection the aircraft rapidly gained about forty knots which caused the aircraft to go above 250kts below 10000 feet. The highest airspeed during the shear I believe to be between 280 and 290 knots. The Captain was the pilot flying and I was communicating with ATC to delete the altitude restriction at ZZZZZ and get a left deviation for severe turbulence and wind shear. Due to this I may not have as clear of a view as the captain as to the altitude and airspeed situation. Approaching ZZZZZ out of about 11000 feet the aircraft encountered a significant downdraft which rapidly descended the aircraft down close to 9000 feet which is the lowest altitude restriction by ZZZZZ. After communication with ATC I believe the restriction was deleted and that we did not pass below 9000 feet regardless. The captain disconnected the autopilot to get the aircraft back up to a more appropriate altitude and back under 250 knots. From here we requested a present position hold to get out of the weather and make a decision. I sent an ACARS message to dispatch asking for more suitable alternates; they sent back ZZZ2. It was immediately clear that in terms of weather ZZZ2 was a great option. Dispatch urged to us to try to get into ZZZ as other aircraft from other directions were able to make it. With the severe turbulence and our radar showing extensive weather between us and the airport we decided to divert. I believe that we might have been able to get into ZZZ but to me it was only a chance. The weather on the other side of ZZZ towards our alternate ZZZ3 was very extensive and would have required major deviation which was not planned for in our alternate fuel calculation. The concern was if we couldn't make it into ZZZ; after deviating around the weather to get to ZZZ3 would we have enough fuel to safely land or make it somewhere else if the weather closed up over ZZZ3. We were getting constant moderate turbulence in the hold and know we would have to fly back through the same turbulence encountered earlier to get to ZZZ. We ended up using the ILS runway XX at ZZZ2 and had an uneventful landing. Even with extensive coordination with dispatch we were unable to get a gate set up for over an hour sitting on the ground in ZZZ2. It was very challenging to get a response from operations on the radio. Eventually they got back to us for a hard stand which allowed passengers who wanted to get off to exit the aircraft. We refueled; had to manually count passengers and bags due to difficulties with the operation. When departing back to ZZZ there was a large wall of thunderstorms that we had to deviate around to get to destination. The weather cleared up in the vicinity of ZZZ and we made a safe landing around XA45 local time.Cause: The deviation above 250kts below 10000 feet was due to wind shear while in severe turbulence. The aircraft rapidly descended from 11000 towards 9000 feet. The diversion to an airport which was not on the initial release was due to an alternate which was not the best option in the first place; but became near impossible to use in flight. Suggestions: ZZZ3 was not the best alternate choice in the first place. Take the time necessary to ensure the release has the best options listed for alternates. The Captain and I were hoping to delay the flight longer than it was but pressure from airport operations; dispatch; and short staffing of gate agents pushed us to depart as soon as the weather showed signs of clearing. We would have liked to delay for an extra 30 minutes to allow further dissipation and passing of the weather. Do not allow the operation to pressure the crew into a premature departure; the pilots make the final decision if the aircraft is to push back from the gate and depart.