The impact of the Madden–Julian oscillation on extreme winter weather over the contiguous United States

Despite its substantial impacts on human society, winter weather is difficult to predict on subseasonal‐to‐seasonal (S2S) timescales. To improve its predictability at longer timescales, this study examines whether the Madden–Julian Oscillation (MJO) has a significant impact on the frequency of extreme winter weather (i.e., heavy accumulations of snow, ice pellets, and freezing rain) over the contiguous United States. We find an increased frequency of extreme winter weather in the Ohio Valley and Mid‐Atlantic regions when MJO enhanced convection is over Africa and the western Indian Ocean, due to imposed lower 850‐hPa temperatures associated with MJO teleconnections. More frequent subfreezing temperatures lead to an increased likelihood of frozen precipitation compared with liquid, increasing the frequency of extreme winter weather. The MJO also increases the frequency of winter weather in the Central Great Plains region of the United States when MJO enhanced convection is over the eastern Indian Ocean and the Maritime Continent. Rather than through effects on temperature, the likely mechanism of increased winter weather over this region is enhanced synoptic forcing that increases overall precipitation. These effects can be seen up to 15 days in advance, suggesting the utility of using the MJO in S2S forecasting of extreme winter weather.