The Influence of Tropical Forecast Errors on Higher Latitude Predictions

The atmospheric response to variations in tropical latent heating extends well beyond its source region, and therefore it is thought that a reduction of tropical forecast errors should also benefit subsequent forecasts over the extratropics. This relationship is evaluated using a conditional skill analysis applied to subseasonal reforecasts from the National Centers for Environmental Prediction Coupled Forecast System and the European Centre for Medium-Range Weather Forecasts Integrated Forecast System. It is shown that there is enhanced or attenuated skill in Northern Hemisphere Weeks 2-4 forecasts when tropical short range precipitation forecasts are "good" or "poor," respectively. This conditional skill is modulated by both El Nino Southern Oscillation and the Madden and Julian Oscillation, particularly in the Integrated Forecast System. The results presented here indicate that midlatitude Weeks 2-4 predictive skill would benefit from improvements in Week 1 tropical performance, particularly for the National Centers for Environmental Prediction system.