Regional Jet 900 (CRJ900)
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Weather / Turbulence; Inflight Event / Encounter Loss Of Aircraft Control
Flight Crew Returned To Clearance; Flight Crew Regained Aircraft Control
Human Factors; Weather
During cruise at 37000 feet in IMC (high stratus clouds) at .78 Mach 10 miles south of NLD we penetrated an embedded thunderstorm. Prior to reaching the storm flight conditions were smooth. Upon recognition of precipitation and onset of turbulence I immediately turned on the fasten seatbelt sign and told the first officer to reduce speed to .75 Mach. I immediately turned on the continuous ignition switch. The turbulence was initially moderate but escalated to severe. We had an altitude change of approximately 37300 then to 36700 in a matter of seconds. Airspeed came within a few knots of maximum. Airspeed; airplane attitude and altitude were uncontrollable for approximately 15 seconds. The autopilot never disengaged and we eventually regained our original altitude after adding some power. We passed through the storm in less than 30 seconds. After passing through it I called to check on the flight attendants and passengers. The flight attendants told me through the intercom they were okay and that the passengers had no injuries and were okay as well. We landed without incident.  If Monterrey Center has weather radar access it would have helped to have been alerted to the embedded thunderstorm prior to reaching it. I will be more proactive about turning on onboard radar when flying in IMC conditions even in smooth air.
CRJ-900 Captain reported loss of control of attitude and altitude for approximately 15 seconds as a result of severe turbulence associated with thunderstorm cell penetration.