Forecast Experiments for the 24–26 January 2000 East Coast storm using the NCEP Eta Model

The 24-26 January 2000 East Coast storm produced severe winter weather in the major metropolitan areas of the eastern United States from North Carolina northward into New England. Snowfall totals in excess of 12 inches were reported at many locations in the mid-Atlantic states. Although the NCEP state-of-the-art operational short range models (32 km Eta and the T170 resolution Aviation run of the global spectral model) predicted offshore cyclogenesis, these model forecasts initialized 12-h to 24-h prior to the event failed to predict the location and intensity of the precipitation in the major metropolitan areas.

Experimental runs of the NCEP Eta Data Assimilation System (EDAS) and the Eta forecast model have been performed in an attempt to isolate features and model/analysis characteristics which may have contributed to the poor performance of the operational models. These experiments can be roughly categorized as follows:

1) DATA ASSIMILATION

Data sensitivity tests, addition of new data types (e.g., satellite radiances); assimilation of observed precipitation ; advanced assimilation techniques (4-dimensional variational analysis)

2) MODIFIED PHYSICS / DYNAMICS

Different convective parameterization schemes (compare operational Betts-Miller-Janjic scheme to Kain-Fritsch, Arakawa-Schubert schemes) ; modified treatment of cloud / cloud water ; non-hydrostatic dynamics ; vertical coordinate (terrain following sigma versus step-mountain eta) ; increased resolution (22 km / 50 levels, 10 km /70 levels)

The presentation will emphasize those changes or combinations of changes which produced forecasts which would have given field forecasters better guidance with a longer lead time than the operational forecast.