Spirit Airlines flight 641 encountered convective turbulence while descending into Louis Armstrong New Orleans International Airport (MSY), New Orleans, Louisiana. As a result of the turbulence, all three flight attendants were injured with two receiving minor injuries and one receiving a serious injury. The aircraft continued to its destination without further incident. According to the captain, the flight crew completed the approach checklist and illuminated the seat belt sign when the airplane was at about flight level (FL)180. As the airplane passed through 12,000 feet, the first officer (FO) made an announcement to the flight attendants to prepare the cabin for landing. According to the lead flight attendant, she made the landing announcement to passengers while the other two flight attendants started final checks from the aft cabin. The lead flight attendant then started the final check from the front of the aircraft. When the lead flight attendant was between rows 6 and 9, the airplane descended through a cloud layer at about 7000 feet and experienced what was described as moderate turbulence by the flight crew. This turbulence led to all three flight attendants falling to the floor. All three flight attendants agreed they needed medical attention and notified the flight crew. The FO called operations and requested for paramedics to meet the airplane. The flight continued to its destination without further incident. Upon arrival at MSY, paramedics met the airplane at the gate, and all flight attendants received medical treatment. The lead flight attendant was transported to the hospital where she was diagnosed with a fractured ankle. Another flight attendant suffered minor injuries to their back and the third suffered minor injuries to their head. Both pilots stated that the cloud layer appeared stable with no vertical development, and there were no indications on the radar that suggested the risk of turbulence. A post-accident review of the weather conditions showed no pilot reports (PIREPs) for turbulence located within a 100 nm radius from the accident location within 2 hours of the accident time. There were no airman’s meteorological information (AIRMETs), significant meteorological information (SIGMETs), or Center Weather Advisories for turbulence or thunderstorm activity for the accident location. Based on weather satellite information and upper air sounding data, the flight encountered convective activity while traversing building cumulus clouds during the descent.