A new routing metric for multi-hop wireless ad hoc networks is presented. The proposed metric is based on the computation of Signal-to-Noise Ratio (SNR) and minimization of wireless network outage probability in a fading environment. This metric improves the Quality-of-Service by reducing dropped packets. Further, by modeling the network with a Trellis diagram and then using Viterbi Algorithm to select the best routing path, we reduce the routing complexity of our approach. Simulation results demonstrate the improvement achieved by implementation of this new metric. Performance of the proposed metric is compared to other commonly used routing metrics such as Minimum Hop Count (MinHop), Expected Transmission Count (ETX) and two other SNR-based metrics in both mobile and stationary networks.