Tuesday, 31 July 2001: 2:00 PM
Experiments with the NCEP Eta model for the 30–31 December 2000 East Coast Snowstorm : sensitivity to initial conditions and sea surface temperature
The 30-31 December 2001 storm produced heavy snowfalls across the northeastern United States, with total storm accumulations in excess of 12" extending from central New Jersey northward into eastern New York and New England. Guidance from both NCEP operational short-range models (the 22-km Meso Eta and the Aviation (AVN) run of the NCEP Global Spectral Model) predicted a significant snowfall event 2-3 days in advance. However, both models exhibited a westward bias in their predicted snowfall patterns. In particular, Eta model forecasts initialized at 12Z 29 December 2000 predicted 5-10 inches of snow over the Baltimore / Washington metropolitan area, where no precipitation was observed. The AVN model for the same initial time predicted about ½ the amount forecast by the Eta model.
Reruns of the Eta model for the 12Z 29 December 2000 were performed with alternate initial conditions. A real-time 22-km Eta parallel which was testing an alternate, high-resolution sea surface temperature analysis predicted 50% less precipitation over eastern Maryland and the Delmarva peninsula then the operational Eta model. A similar signal was seen when the Eta forecast was initialized from the AVN analysis instead of that from the Eta Data Assimilation System (EDAS). An Eta forecast rerun using both AVN initial conditions and the high-resolution sea surface temperature produced the best forecast in the mid-Atlantic region, with no precipitation predicted over eastern Maryland.
Details of these experiments will be presented, with emphasis on the performance and deficiencies of the EDAS during this event which may have led to the poor Eta model forecasts.