Warmer winter is expected for 2023-2024, thanks to El Niño and the Woolly Bear caterpillar

Winter in Michigan always has the elements of snow and ice. However, this year El Niño is in place heading into winter for the first time in four years.

Understanding the jet stream

Jet streams are relatively narrow bands of strong wind in the upper levels of the atmosphere, typically occurring around 30,000 feet (9,100 meters) in elevation.

Within jet streams, the winds blow from west to east, but the band often shifts north and south because jet streams follow the boundaries between hot and cold air. Since these hot and cold air boundaries are most pronounced in winter, jet streams are the strongest during both the northern and southern hemisphere winters.

As its name implies, the jet stream is essentially a river of fast-moving air in the atmosphere at about the altitude where airplanes fly. It is typically a few hundred miles across, and jets can indeed save a lot of fuel if they can fly within this air current, generally from west to east.

Jet streams also have significant implications for our weather on the ground, as they more or less steer storm systems that affect the mid-latitudes. That is, they in large part determine whether parts of the United States, which lies almost entirely in the mid-latitudes between the tropics and poles in the Northern Hemisphere, will see stormy or serene weather.

Three weather patterns

As always with the weather, the situation is complex. But one of the more useful signals in a forecaster’s arsenal is the El Niño Southern Oscillation (ENSO) in the tropical Pacific Ocean, which vacillates between warmer sea surface temperatures called El Niño, cooler ones named La Niña, and neutral conditions. This broad pattern has widespread weather implications, including the location of the jet stream.

El Niño, or “Little Boy,” is one of three weather patterns that make up the ENSO. With this pattern present, a warming of the surface of the eastern Pacific Ocean occurs, and that coincides with weaker trade winds. Oppositely, in years when we have La Niña, or “Little Girl,” weather pattern a cooling of the ocean surface and an increase in the trade winds is known to happen. When neither occurred, it is considered neutral conditions to make up the three.

Understanding the winter forecast

The National Oceanic and Atmospheric Administration (NOAA) has released its winter outlook for the United States. From December 2023 through February 2024, NOAA predicts wetter-than-average conditions for northern Alaska, portions of the West, the southern Plains, Southeast, Gulf Coast, and lower mid-Atlantic and drier-than-average conditions across the northern tier of the U.S., especially in the northern Rockies and High Plains and near the Great Lakes.

According to the NOAA Winter Outlook, there’s a 40-50% chance Michigan will see above-average seasonal temperatures through February, which is the case for most of the Great Lakes region.

NOAA’s seasonal outlooks provide the likelihood that temperatures and total precipitation amounts will be above-, near- or below-average, and how drought conditions are anticipated to change in the months ahead. The outlook does not project seasonal snowfall accumulations as snow forecasts are generally not predictable more than a week in advance.

Woolly Bear folklore

According to folklore, the amount of black on the woolly bear caterpillar in autumn varies proportionately with the severity of the coming winter in the locality where it is found. The longer the woolly bear’s black bands, the longer, colder, snowier, and more severe the winter will be. Similarly, the width of the middle brown band is associated with the upcoming winter.

The story goes that a wider brown band indicates a milder winter is ahead. Caterpillars found this year have bands encompassing more than half of their bodies, which folklore would indicate portend a warmer and more pleasant winter season ahead.

The position of the longest black band supposedly indicates which part of winter will be coldest or hardest. If the head end of the caterpillar has more dark coat, the beginning of winter will be severe. If the tail end has more, the end of winter will be cold. In addition, the woolly bear caterpillar has 13 segments to its body, which traditional forecasters say corresponds to the 13 weeks of winter.

As with most folklore, there are two other versions of this story. The first one says that the woolly bear caterpillar’s coat will indicate the upcoming winter’s severity. So, if its coat is very woolly, it will be a cold winter.

The final version deals with the woolly bear caterpillar’s direction of travel of the worms. It is said that woolly bears crawling in a southerly direction are trying to escape the cold winter conditions of the north. On the other hand, a woolly bear crawling on a northward path would indicate a mild winter.

The woolly bear is more than just a caterpillar, it is an indication of weather found across the United States, Canada and Mexico.

So whether you’re team science, or team folklore, it looks like we will be having a mild winter in Southwest Michigan.