Outdoor digital displays have become increasingly popular and common for smart city applications, and more recently provides a concealment solution and integration point for outdoor communications devices meant to be attached to buildings, streetlamps, or traffic poles. Given the larger energy requirements for powering next generation 5G cellular networks, these devices create unique difficulties in developing and evaluating thermal management solutions. The present study develops and validates the extreme condition transient (ECT) climate model using a CFD/HT numerical model, to evaluate diurnal thermal responses from a representative 5G small cell devices. The model is validated for local conditions present in Atlanta, GA for two unique days. The thermal response from the ECT climate model is presented alongside three real case study locations, Miami, FL, New York City, NY, and Phoenix, AZ.