Theoretical analysis and a full numerical simulation of the electromagnet ically induced transparency model are performed under detuning conditions for a closed three_level ultracold atomic system in which a signal field can be stored and retrieved. Numerical results confirm the theory that the system can be prep ared in dark states only under resonant conditions between the fields and the a tomic transitions. The signal field is partially stored in the ultracold atomic medium with the increase of detuning and an enhanced negative group velocity of t he physically vanishing signal pulse appears. In the case of a symmetrical detun ing (red or blue detuning), no remarkable changes of the storage process occur.