La Niña Impacts 

and Outlook

Great Lakes Region

November 2020

Typical La Niña Winter Pattern

Highlights for the Basin

A La Niña develops when sea surface 

temperatures in the eastern equatorial 

Pacific are consistently cooler than average 

for an extended period of time. These cool 

waters affect the location of jet streams, 

which impacts North America. The most 

notable impacts occur in the winter, when 

the wind patterns in the atmosphere are 

strongest. 

While no two La Niña events are alike, 

there are some general patterns that are 

predictable. For instance, the polar jet 

stream is typically farther south during La 

Niña winters than usual. 

This pattern typically brings below-normal 

temperatures to much of the Great Lakes 

region, particularly across the western Great 

Lakes area. The southern Great Lakes may 

also see a slight shift toward wetter-thannormal conditions.

The image above shows the typical pattern in the winter during La Niña 

events. The polar jet stream tends to stay to the south of the Great Lakes 

region, while the Pacific jet stream tends to track closely along the Pacific 

Northwest, bringing increased chances for moisture during the winter in 

the Great Lakes basin.

Image courtesy of the National Oceanic and Atmospheric Administration.

La Niña Outlook

Winter Temperature and Precipitation Outlooks

Valid for December 2020 - February 2021

Temperature Precipitation

Contact: Veronica Fall (vfall@illinois.edu)

Doug Kluck (doug.kluck@noaa.gov)

EC: Equal chances of above, near, or below normal 

A: Above normal, B: Below normal

As of October, the temperature outlook indicates that most of the western 

and central region of the Great Lakes basin has equal chances for above-, 

below- and near-normal temperatures while the Lake Erie and Ontario 

basins have a slightly enhanced chance for above-normal temperatures.

Meanwhile, there is an enhanced chance for above-normal precipitation 

for a majority of the Great Lakes region, except for the far eastern region 

around the Lake Ontario basin which has equal chances for above-, belowand near-normal precipitation. Increased precipitation may have positive 

implications, such as increased snowpack and winter recreation, along 

with negative impacts like increased runoff in the spring. 

La Niña Probability

Winter 2020-2021

La Niña conditions have continued this fall 

and forecasts indicate that this La Niña 

will strengthen, peaking as a moderate 

or even strong event in late fall or early 

winter. According to the Climate Prediction 

Center, there is a greater than 85% chance 

that these conditions will last through the 

winter and about an 60% chance that La 

Niña will continue into the early spring, 

as shown in the image above. A La Niña 

Advisory is currently in effect.

Great Lakes Region La Niña Impacts and Outlook | November 2020 

https://www.drought.gov/drought/resources/reports
Potential Winter and Spring Impacts

Agriculture

Courtesy of M. Longstroth.

Winters associated with La Niña 

tend to be cold with above-average 

precipitation and could negatively 

impact winter wheat and fruit 

orchards. However, because La Niña 

winters typically result in increased 

snowpack, this could insulate these 

crops to cold air outbreaks and harsh 

wind. Harsher winter temperatures 

could be negative for livestock 

producers due to increased operating 

costs and animal stress. La Niña 

could affect commodity prices due to 

negative impacts internationally.

Economy

Courtesy of Illinois-Indiana Sea Grant

Cold and wet winters with aboveaverage snowfall can impact some 

economic sectors. The largest negative 

impacts are increases in home heating 

costs, snow removal expenses and 

difficulties in overland transportation. 

Sectors that depend on winter 

weather conditions, like winter 

recreation, snow removal businesses, 

towing companies and road salt sales, 

will likely see a benefit from increased 

snowfall. More ice on the Great Lakes 

could potentially delay the navigation 

season for shipping in the spring.

Water Levels and Ice

Courtesy of Illinois-Indiana Sea Grant.

With the increase in chances for 

above-normal precipitation, the 

likelihood of more snow accumulation 

is greater. The potential for increased 

snowpack may lead to a higher chance 

for more runoff and flooding in the 

spring. The potential for more ice 

later in the winter due to cooler-thannormal conditions may result in less 

evaporation, thus keeping lake levels 

high. Increased runoff and decreased 

evaporation may take less water away 

from the system than normal. These 

factors could lead to higher lake levels.

Comparisons and Limitations

Winter Conditions During Past La Niña Years

Maps courtesy of the Midwestern Regional Climate Center

The maps above illustrate the winter conditions of the most recent La Niña 

event in 2017-2018. Much of the western basin was cooler than average (above 

left) and precipitation was near-to-above normal (above right). Please note that 

each La Niña is different and La Niña impacts can be limited by many factors, 

including being overcome by short-term and local weather and climate events.

While past La Niña events can help inform forecasters about certain conditions, 

there are some limitations. For instance, in the Great Lakes La Niña is not

known to impact: 1) first freeze in the fall, 2) last freeze in the spring, 3) 

potential for ice storms or blizzards, 4) track or intensity of any single weather 

system, or 5) potential for springtime drought or flooding.

Great Lakes Partners

Midwestern Regional Climate Center 

mrcc.illinois.edu

National Oceanic and Atmospheric Administration 

www.noaa.gov

 NOAA NCEI 

 www.ncei.noaa.gov

 Great Lakes Environmental Research Lab 

 www.glerl.noaa.gov

 NOAA NWS Climate Prediction Center

 www.cpc.ncep.noaa.gov

 NOAA Great Lakes Sea Grant Network 

 www.seagrant.noaa.gov 

 North Central River Forecast Center 

 www.weather.gov/ncrfc

 Ohio River Forecast Center 

 www.weather.gov/ohrfc

Great Lakes Integrated Sciences and 

Assessments 

glisa.umich.edu

American Association of State Climatologists

www.stateclimate.org

National Integrated Drought Information 

System 

www.drought.gov

USDA Midwest Climate Hub

www.climatehubs.usda.gov

Great Lakes Region La Niña Impacts and Outlook | November 2020 

https://www.drought.gov/drought/resources/reports

Contact: Veronica Fall (vfall@illinois.edu)

Doug Kluck (doug.kluck@noaa.gov)