The Epic Eastern North American Warm Episode of March 2012

A historic warm episode occurred over much of eastern North America in March 2012 resulting in the warmest March on record over the contiguous United States. During this warm episode, over 7700 daily record maximum temperatures were set in the United States, with over 7500 daily record high minimum temperatures. This period of warmth was caused by a strong and persistent mid-tropospheric ridge. Southerly flow on the western flank of this ridge resulted in precipitable water anomalies exceeding six standard deviations above normal over eastern North America, not only aiding in the persistence of warm overnight lows, but also a period of heavy rainfall and severe weather in the southern Plains.

The most anomalous warm period was observed from 13 to 23 March 2012. During this time 500-hPa height, 850-hPa temperature, and precipitable water anomalies in excess of two standard deviations above normal were common over a large portion of eastern North America. Daily high temperatures in the Midwest and Great Lakes regions were often 5 to 20 °C above normal. In fact, some locations experienced minimum temperatures that were higher than previous record maximum temperatures for the date.

This study examines the persistent pattern which brought the period of epic warmth to eastern North America in March 2012. It is shown that this warm episode shared all the characteristics associated with a summer-time heat wave. The historical significance of this event is examined by comparing it to another March warm episode in 1945 as well as a well-known cold episode that occurred in January 1994. Finally, the predictability of this event is examined using the National Centers for Environmental Prediction's Global Ensemble Forecast System.