Inter-annual variations in the tropical Pacific sea surface temperatures (SSTs) related to ENSO are known to influence surface climate anomalies over North America1-2. In this paper, using a suite of atmospheric general circulation model simulations, it is demonstrated that these climate anomalies are an end result of two distinct processes. While the first is a direct response to the tropical Pacific SSTs, the second is due to changes in snow amount. This secondary influence is found to have a strong positive feedback on the direct response, and greatly enhances the North American surface temperature climate anomalies associated with ENSO. Implications of this feedback mechanism on seasonal climate predictions and greenhouse gas induced climate changes are discussed.