Regional Super El Niño Impacts: Midwest U.S.

There are differences among seasonal forecast models, and in areas where those differences are larger, confidence in the forecast is lower. We don’t yet know which model will be the most accurate. The six seasonal forecast models used as part of the North American Multi-Model Ensemble display a range of winter precipitation forecasts. Two of the models predict generally drier than normal conditions this winter. Three models predict a wet winter over most of the region, and one model forecasts near-normal precipitation across much of the Midwest. The disagreement indicates uncertainty in winter outcomes, and the differences can be substantial. For example, one model indicates that eastern Ohio could receive more than one and a half times its usual winter precipitation, while another predicts a slightly drier than normal winter. A majority of the models call for a warmer than normal winter across the Upper Midwest, and a majority indicate near to below normal temperatures for Missouri. Winter temperature forecasts are less certain elsewhere in the region. For example, winter temperature predictions for parts of Iowa and Missouri range from a few degrees below normal to a little above normal. 

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Differences between winter forecasts for the Midwest can be challenging for managers, but forecasts combined with current conditions can highlight areas for attention and observation as the fall and winter progress. 

For example, parts of the Upper Midwest that are already experiencing drought could see drought remain or worsen if warmer, drier forecasts are correct. Drought can have a range of impacts from enhancing fire risk to reducing water quality, stressing plants and animals, and even potentially hindering river transportation. Many of these impacts of persistent drought may not be fully experienced until the spring. 

In the Upper Midwest, there is a reasonably strong signal for warmer than normal temperatures that could lead to a reduction in winter snow and ice. In places where winter snow and ice are common, loss of winter can have a wide range of impacts. 

• Reduced snowpack and warming winter may lead to earlier, lower peak flow in northern streams, creating warmer water temperatures that could negatively affect coldwater species such as brook trout. 
• Reduced lake ice cover can expose shorelines to erosion and increase winter wave action. This may degrade nearshore fish habitat, which is critical to fish spawning and reproduction. Warmer water and longer ice-free period will likely negatively affect coldwater lake species such as cisco. Warmer temperatures and loss of ice cover can reduce oxygen availability leading to fish kills.
• Warmer winter temperatures and a lack of cold spells will reduce lake ice cover and stability. For ice fishing, this will increase safety risks and shorten the season.  
• A warmer winter, especially if there is more precipitation on unfrozen ground, could increase erosion and soil damage from timber-harvest vehicles. This can create downstream impacts if combined with increased precipitation causing runoff to streams and rivers. Managers may face reduced winter access to forest resources in the Upper Midwest. 
• Mild winter temperatures and decreased snowpack could increase deer browsing, heightening pressure on plant regeneration. 
• In the northern Midwest, where there is greater model agreement for decreased precipitation and increased winter temperatures, insulation, refuge, and camouflage will decline for boreal wildlife like snowshoe hare, ruffed grouse, and spruce grouse. 
• A warmer winter will likely create more suitable conditions for pests and pathogens, leading to expansion and increased pressure. 
• Tick survival, presence, and pathogen transmission are likely to increase in warmer winter conditions in the Midwest. Winter tick infestations on moose, and associated mortality risks, will be of greater concern in a warmer winter.  
• Decreased extreme cold and overall mild winter will increase the survival, prevalence, and potentially facilitate the expansion of emerald ash borer and other forest and agriculture pests.