The Difference in Summer Vs. Winter Seasonal Forecasts.

During the winter, temperature and precipitation anomalies are strongly correlated over large spatial scales and are related to climate modes or teleconnection indices that explain a large fraction of the variance in the atmospheric circulation.  These climate modes represent dynamical processes such as air-sea coupling or troposphere-stratosphere coupling.    In contrast summer temperature and precipitation anomalies are on smaller scales and are only weakly correlated with large-scale climate modes.  Instead thermodynamics are much more important in summer such as the proportion of sensible and latent heating and convective processes.  Therefore a successful prediction of winter weather relies on correctly capturing large-scale dynamic forcing that are active during the winter season.  In contrast a successful prediction of summer weather relies on capturing the small-scale radiative and thermodynamic processes that characterize the summer season.  For AER winter forecasts we use predictions of the large-scale modes of the El Niño Southern Oscillation (ENSO) and the Arctic Oscillation (AO) to generate accurate winter forecasts.  In summer, AER forecasts rely more heavily on soil moisture, persistence and long-term trends to generate accurate winter forecasts.  Maybe somewhat ironically the complex dynamical models have performed better in predicting the thermodynamically sensitive summer season relative to the dynamically sensitive winter season.  The differences in winter compared to summer seasonal forecasts have important implications for the ability of seasonal forecasts to service the energy and agriculture sectors.