| By Mike Ekberg, manager of water resources monitoring and analysis It’s the beginning of November and winter is just around the corner. What kind of a winter can we expect in the Miami Valley this year? Winter 2020–2021 might be wetter than normal with frequent storm events tracking across our region. Wetter than normal means above-average winter precipitation, including rain, sleet, and snow. One factor that favors this outcome is the forecasted presence of a strong La Niña pattern in the tropical Pacific Ocean this winter. |
Credit – | La Niña present in the tropical Pacific Ocean La Niña is an atmospheric pattern characterized by stronger-than-normal trade winds and cooler-than-normal ocean temperatures in the equatorial Pacific Ocean. These conditions are currently present, and the National Oceanic and Atmospheric Administration (NOAA) is forecasting this pattern to persist and strengthen as we move through the winter months. How does an atmospheric phenomenon such as La Niña thousands of miles away in the tropical Pacific Ocean influence winter weather in the Miami Valley? |
 Credit – https://www.climate.gov/news-features/blogs/enso/september-2020-enso-update-la-ni%C3%B1a-here |
| Wetter-than-normal winter conditions favored in the Miami Valley The answer lies in La Niña’s influence on the position of the polar jet stream across North America. According to the National Weather Service, jet streams are narrow bands of strong wind in the upper atmosphere that blow from west to east. The polar jet stream often marks the boundary between cold and warm air masses across North America, and it often acts as a transport mechanism for storm systems across the United States. La Niñas tend to cause the polar jet stream to dip south over the Midwest and the Ohio Valley. This creates favorable conditions for winter storm systems to track across this region. The result is lots of moisture delivery, leading to above-average precipitation. So there you have it, we can bank on a wetter–than-normal winter this year, correct? Not so fast, La Niña is just one of many factors impacting winters in the Miami Valley. |
 La Niña can lead to above-average precipitation in winter. |
| Other factors influence local weather, too La Niña events tend to be persistent, lasting six to 18 months. There are other global atmospheric circulation patterns or teleconnections such as the Pacific/North American (PNA), Arctic Oscillation (AO), and the North Atlantic Oscillation (NAO) which fluctuate on shorter time scales. These teleconnections also influence the path of the jet stream across the United States and may interact with La Niña amplifying or canceling out its impact. Predicting these teleconnections patterns can be difficult. Local factors such as soil moisture conditions and snow cover can also influence winter precipitation in the Miami Valley. Long-term climate trends may also play a role. Obviously, there is a lot of uncertainty when it comes to making predictions about how winter 2020–2021 will turn out. Still, it’s fun to look at all the factors and give it a shot! MCD ready to respond no matter what winter 2020-2021 brings No matter what this winter brings, there is one thing the Miami Valley region can count on. MCD is ready to respond to whatever weather comes our way. The MCD flood protection system has been in place for nearly 100 years, significantly reducing flooding risk in cities along the Great Miami River. If this winter turns out to be wetter than normal as predicted, MCD will be ready to respond. |
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