Forecasting extreme cold snaps in the Northeast: Weather and Climate

Extreme cold spikes in wintertime temperature spike demand for heating and natural gas. Short-term temperature extremes, both hot and cold, are highly sensitive to climate time scales as climate variability and change effect both the mean and variance structure of daily temperatures as they evolve over a season. We consider wintertime cold snaps over a large region of the Northeastern and Midwestern United States according to how local cold temperature thresholds (5th percentiles of local wintertime temperature recorded at each of almost 500 stations) are exceeded on daily timescales. A regional magnitude index reflecting the temperature intensity, duration and spatial extent of extreme cold spells is computed for 61 winters from 1948/9 to 2008/9 and for each day of each event. Observed variability of regional cold spells is then examined on timescales ranging from daily to interdecadal and scrutinized with respect to the climatic controls on their synoptic causes. Relationships with known climate modes (ENSO, NAO, PDO, PSV, etc.) as well as other relevant objectively derived circulation and land-surface patterns are then used to develop sophisticated models and simple rule-of-thumb techniques for seasonal and improved medium-range probabilistic prediction of cold snap magnitude. Anthropogenic forcing is assessed and integrated into the predictive methodology. The main components of cold spells, i.e. intensity, duration and spatial extent, are explicitly considered. These forecasting tools are designed for straightforward operational application by practicing meteorologists working in energy load forecasting.