The Seasonality and Regionality of MJO Impacts on North American Temperature

It is widely accepted that the Madden-Julian Oscillation's (MJO) influence on North American temperature is strongest in winter. A growing body of literature demonstrates that the MJO also influences North American weather in other seasons. Here we use observations to investigate the seasonality and regionality of the MJO's impact on weather station daily maximum air temperature over North America (NA). Consistent with previous work, we find the strongest MJO signal in temperatures over eastern NA and Alaska during winter. However, the peak MJO signals over much of central NA, western NA, and south Texas occur outside of winter. We investigate how this translates to forecast skill and conduct leave-one-out cross-validated empirical forecasts of maximum surface air temperature using the phase of the MJO and lead time as predictors. Our results suggest the potential for more skillful long-range forecasts of weather over NA during spring, summer, and fall. Plain Language Summary Large, organized storms in the tropical Indian and West Pacific Oceans can excite waves in the atmosphere that influence weather over North America. Much of our understanding of this process focuses on the northern winter season, but we show evidence that for some parts of North America the storms also influence daily maximum temperature during spring, summer, or fall. Our results suggest the potential for more skillful long-range forecasts of North American weather during spring, summer, and fall.