GRAND RAPIDS, Mich. (WOOD) — One of the most influential climate patterns for the United States is the El Niño Southern Oscillation, or ENSO. With a periodicity of about three to seven years, it involves changes in ocean temperatures across the Pacific Ocean.
Along the equator, the trade winds normally blow from the east to the west.
In some cases, those winds can weaken of even switch direction to blow from west to east. This allows warmer water to build in the central and eastern Pacific. When that happens, the central and eastern Pacific sees an increase in rainfall and the western Pacific sees a decrease in rainfall. The pattern of warm water building in the central and eastern Pacific is the warm phase of ENSO and it is called El Niño.
In an El Niño pattern, the warmer temperatures in the central and eastern Pacific manipulate the position of the jet stream. A center of low pressure often builds in the Gulf of Alaska. A ridge of high pressure will set up over Western Canada and low pressure tends to settle in over the southeast U.S. For the Great Lakes region, this pattern often leads to a slightly drier and slightly warmer winter.
La Niña is the cool phase of ENSO caused by a strengthening of the easterly trade winds. The warm water is pushed back toward Asia and the central and eastern Pacific see an upwelling of cool water. Rainfall increases in the western Pacific and decreases in the central and eastern Pacific.
During a La Niña cycle, the Great Lakes region often sees slightly more precipitation than normal and temperatures that are close to normal.
We are expecting an ENSO neutral year for the winter of 2019-2020, meaning there is a lack of an El Niño or La Niña. In an ENSO neutral year, our winter weather is more dependent upon different climate patterns.
The Arctic Oscillation, an atmospheric circulation pattern that drives the jet stream, is one such pattern that will likely determine our winter weather. Another example is the Madden-Julian Oscillation, a pattern of clouds and rainfall around the equator. In an ENSO neutral year, the Great Lakes region often leans toward a colder than normal winter.