Regional Super El Niño Impacts: North Central 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. Overall, the six seasonal forecast models used as part of the North American Multi-Model Ensemble show considerably more agreement on temperature than on precipitation. Most of the models indicate above-average winter temperatures across the northern tier of the North Central region, particularly Montana and the Dakotas, making warmth the most consistent signal in the current forecast. This is also broadly consistent with the historical response during strong El Niño winters. The models show substantially greater disagreement in Colorado, Wyoming, Nebraska, and Kansas, although warmer conditions remain a plausible outcome across much of the region particularly given the additional warming from climate change. 

The precipitation forecasts show a weaker but still recognizable pattern: more models favor wetter-than-normal conditions across the southern and central portions of the region, particularly Colorado, Nebraska, and Kansas, while precipitation forecasts are more mixed across Montana, northern Wyoming, and the Dakotas. This general pattern is consistent with the historical tendency for El Niño to shift the winter storm track southward, increasing precipitation across the southern tier while reducing storminess across portions of the Northern Rockies. However, the differences among the models are substantial enough that precipitation should be considered a lower-confidence component of the forecast. The model comparison therefore supports a higher-confidence message about warmth in the northern tier and a lower-confidence, north–south gradient in precipitation. Differences among the models are themselves useful information: where the models diverge, confidence in the seasonal forecast is lower, and the winter may be strongly influenced by other atmospheric patterns and individual storm tracks. 

The strongest management signal for the North Central region is the possibility of warmer winter conditions across the northern tier, combined with north–south differences in precipitation and snow. Managers in Montana, northern Wyoming, and the Dakotas should consider the potential for reduced snow accumulation and earlier snowmelt, particularly at lower and middle elevations where warmer temperatures can shift precipitation from snow to rain and accelerate loss of existing snowpack. This could affect spring runoff timing, soil moisture, water availability, and cold-season habitat conditions. At the same time, managers in Colorado, Kansas, and Nebraska should be prepared for the possibility of wetter-than-normal winter conditions and, at higher elevations in Colorado, increased snow accumulation. Increased precipitation can improve water availability and soil moisture but can also increase the potential for flooding, erosion, rain-on-snow events, and other impacts from individual high-precipitation storms. 

These conditions also have implications for vegetation and wildfire management. A wet winter and increased spring moisture can benefit plant growth and water availability, but in water-limited ecosystems, greater winter and spring moisture can also produce more grass and herbaceous biomass that becomes available as fine fuel later in the summer. Conversely, reduced mountain snowpack and earlier snowmelt in the northern part of the region could contribute to earlier drying of soils and vegetation. Because the precipitation signal is considerably less consistent than the temperature signal, managers should avoid treating the El Niño outlook as a deterministic forecast. Instead, it can be used to identify plausible shifts in risk and opportunities for early preparation, while updating decisions as the information on winter precipitation, snowpack, and soil moisture become more certain. 
 

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