What Will 2020-2021 Winter Bring?

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 – https://sites.google.com/site/elninoandlanina/la-nina
 
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.

MCD monitoring winter weather systems whether mild or wild

Like it or not, winter 2018 – 2019 is upon us. What kind of winter can we expect in the Miami Valley this year? Will it be cold and snowy, or mild and dry?

It’s hard to say, according to the National Oceanic and Atmosphere Administration (NOAA). The go-to signs that often signal winter weather patterns are slow to give away their secrets this year.

The bottom line: It’s likely we’ll see cycles of mild weather as well as periods when arctic air descends our way as shorter term influences play out.

Whatever winter brings, MCD will monitor upcoming weather systems, preparing for any flood protection response needed in the communities we serve.

Read on to learn more about El Nino, Arctic Oscillation and more influences on our winter weather patterns 

Teleconnections in meteorology refer to large-scale patterns of pressure and temperature in the earth’s atmosphere that impact weather globally. Three teleconnections that influence winter weather in the Miami Valley include the El Niño –Southern Oscillation (ENSO), the Arctic Oscillation (AO), and the North Atlantic Oscillation (NAO).

ENSO exerts a strong influence on the path of winter storm systems as they track across the United States. ENSO cycles tend to operate on timescales of at least several months and have long-lasting influences on global weather patterns. There are three phases to the ENSO cycle: El Niño, Neutral, and La Niña. Each of these phases impacts winter weather across the United States in different ways.

Locally:

  • Strong El Niños tend to result in milder and drier winters in the Miami Valley.
  • Strong La Niña winters tend to be wetter than normal.
  • Neutral conditions tend to result in colder than normal winters.

ENSO impacts winter weather in the Miami Valley by influencing the position of the Jet Stream and the track of storm systems across our region. AO and NAO also influence winters in the Miami Valley and add complexity to seasonal forecasts.

AO refers to changing atmospheric pressure over the arctic region of the globe.

  • Positive AOs tend to keep cold arctic air confined to northern latitudes. Negative AOs often plunge arctic air masses south into the eastern United States – think polar vortex.
  • AO cycles can be forecast only about two weeks ahead, so their use in making seasonal forecasts is somewhat limited.

NAO measures the difference in atmospheric sea level pressure between Iceland in the North Atlantic Ocean and the Azores in the Atlantic Ocean off the coast of Northern Africa. Like the AO, the NAO has a positive and negative phase.

  • Positive NAOs are generally associated with warmer-than -normal temperatures in the eastern United States.
  • Negative NAOs tend to bring colder temperatures to the eastern United States.

Current atmospheric signals
NOAA forecasters think there is a 90-percent chance of El Niño conditions developing in the equatorial Pacific Ocean this year. Even if it does, it’s not expected to be a strong one. Weak El Niños do not exert as much of an influence on local winter weather as strong El Niños. So this year’s ENSO signal isn’t giving a strong signal as to how winter 2018 – 2019 will unfold.

The AO was in a negative phase throughout November allowing arctic air masses to travel south. This favored colder-than-normal temperatures in the Miami Valley, which is exactly what we got. The AO is now in a positive phase, which tends to keep cold air masses bottled up in the arctic. This favors more seasonable temperatures in the Miami Valley for the time being. NOAA is forecasting a continuation of positive AO conditions for the next week or so.

50:50 chances of a mild/cold or wet/dry winter
So what does this all mean?  NOAA published its 2018 – 2019 Winter Outlook for the United States, and the outlook is summarized in the two maps below.

The first map shows the temperature outlook. Much of the western United States is expected to have above-normal temperatures this winter. Southwest Ohio is colored white meaning there is an equal chance of above or below normal temperatures.

The second map shows the precipitation outlook. Above-normal precipitation is expected across much of the southern United States. Pockets of below-normal precipitation are expected across the Dakotas and Montana as well as the Great Lakes region. Once again, southwest Ohio is colored white meaning we have an equal chance of above-normal or below-normal precipitation.

Winter 2018 – 2019 – Anybody’s guess
Based on ENSO, AO and NAO information, it’s likely we’ll see cycles of mild weather as well as periods when arctic air descends our way as shorter term fluctuations in AO and NAO cycles play out. On top of all that is the simple randomness of local weather, making seasonal forecasting difficult at best!

Hoping for a mild, dry winter? You might be disappointed

El Niño gone/ La Niña here

Winter 2016-2017 is upon the Dayton region, and from the looks of things it’s likely to be very different winter than winter 2015-2016. A major reason for the change is the strong El Niño conditions which persisted throughout winter 2015-2016 are gone. La Niña conditions have taken their place. However, the current La Niña is weak, and its impact on local weather will probably not be as great as the 2015–2016 El Niño event.

La Niña winters tend to bring moisture to the Ohio Valley

La Niña conditions occur when equatorial sea surface temperatures are below average in the central and east-central Pacific Ocean. This is the exact opposite of what occurs during an El Niño. Like El Niño, La Niña impacts global weather patterns by influencing the position of the polar and Pacific jet streams. During La Niña winters, the polar jetstream tends to dive south over North America. The polar jet stream brings cold air and storm systems to northern portions of the United States.

la-nina-graphic

According to National Ocean and Atmospheric Administration, we can expect La Niña conditions to persist through February 2017. After February, its likely La Niña will transition to neutral conditions sometime during spring 2017. Neutral conditions mean that neither El Niño nor La Niña conditions are present in the equatorial Pacific Ocean.

So what does this mean for our region in terms of winter weather?

Winter 2016 – 2017 is likely to be wetter and cooler

The odds favor a wetter and cooler winter 2016 – 2017 compared to winter 2015 – 2016. Is this a guarantee? No it’s not. There are a multitude of other climatic factors at play in determining winter weather outcomes in our region. El Niño and La Niña events are just one of those factors.