Linkage between NAO/ENSO phasing and snowfall in North Carolina

Five to seven days before a winter storm impacts the Southeast US, many irresolvable details tend to reduce confidence in forecasting such events. However, predictable trends and interactions between large-scale climate patterns such as the NAO and ENSO can offer some guidance during this time period. A spectral analysis of daily NAO indices reveals the NAO has a recurring period of approximately 20 days during the winter. In addition, a study over a pilot domain of North Carolina comparing NAO and ENSO indices with snowfall data indicates that a negative-phase, west-based NAO and positive-phase ENSO provide the most favorable setup leading into a potential winter weather event. As an event approaches, we observe that winter weather events are more likely if the NAO's phase shifts from negative to near-neutral, rather than if the NAO's phase remains strongly negative, based on the physical linkage between the NAO and synoptic-scale storm evolution. Recognizing this favorable large-scale pattern despite divergent small-scale model solutions, forecasters could increase warning time for significant winter weather events across the Southeast US.