Applying Forecast Track Diagnostics in High-Impact Northeast Winter Storms: Climatology and Case Analysis

A conventional forecasting notion is that as lead time decreases, numerical weather prediction models exhibit a westward trend in the forecast position of low-pressure systems along the East Coast of the U.S. This westward trend, which may turn seemingly weak ocean cyclones into high-impact weather events for the Northeast U.S., is sometimes attributed to the representation of latent heat release in the NWP models downstream of the trough associated with the incipient cyclone. Specifically, it is commonly believed that the underrepresentation of latent heating at longer lead times prevents a NWP forecast from properly depicting the negative tilt of the trough, and the reduction of the half wavelength between the cyclone and downstream ridge, that is commonly observed.

A climatology of ensemble forecasts of high-impact Northeast winter storms initialized at short to medium-range lead times was constructed using the Global Ensemble Forecast System (GEFS) Reforecast version 2. The climatology utilizes cyclone forecast position ellipses following the methodology of Hamill et al. (2011) to quantify the nature of the cyclone position uncertainty at various forecast lead times by examining the position ellipse axes, representing the directions of greatest and smallest cyclone position uncertainty. To demonstrate this method, the winter storm of 13–15 March 2017 is used as a representative case study. The case analysis will highlight the cyclone track uncertainty by examining the role of the physical processes linked to latent heat release in ensemble members grouped by location in the position ellipse. The application of these results from the GEFS reforecast analysis will then be applied to the operational ECMWF ensemble forecasts available during the event.