Source: Corey Davis, NC CLIMATE OFFICE, 11/19/19

When assessing our likely wintertime weather conditions, we often start with ENSO, or the El Niño/Southern Oscillation. This pattern, which describes the cyclical warming and cooling of sea surface temperatures across the equatorial Pacific Ocean and the atmospheric circulation changes that it causes, is usually the best long-range predictor of our winter conditions.

However, ENSO doesn't offer us many clues when it's in a neutral state -- defined by Pacific sea surface temperature anomalies within a half-degree of normal.

That's the case entering this winter, so to better understand what an ENSO-neutral winter looks like in North Carolina, we've dug through the data and attempted to address some common questions and misconceptions.

1. What are ENSO's impacts again anyway?

The beating heart of ENSO is the cyclical change in sea surface temperatures across the central Pacific that tend to go from warm (El Niño) to cool (La Niña) phases every one to three years.

These changes are long-lived and widespread enough -- sometimes spanning more than halfway across the world's largest ocean -- that they can induce shifts in atmospheric circulations across the globe.

Among those is the subtropical jet stream, which separates warm, tropical air from cooler, continental air. The buildup of warm water in the Pacific during an El Niño event also warms the air above the ocean surface, and an increased temperature difference between the equator and the north pole enhances the subtropical jet stream.

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