Initial Conditions and SREF Forecasts for the 6-7 January 2002 Northeast US Snowstorm

Graphic courtesy of NWS WFO State College, PA

Abstract

This case discusses the failure of the Short-Range Ensemble Forecast (SREF) system in catching the occurrence of a major snowfall on 6-7 January 2002 over the interior northern Mid Atlantic States and New England. The totals for this storm can be seen in the graphic shown above, with up to 14" in central PA and 17" in the Albany NY area.

The storm was poorly predicted by both the operational numerical weather prediction (NWP) models and the SREFs. This poor performance can be traced back to difficulties in capturing the initial atmospheric state in a series of NWP and SREF forecasts.

In this case, we will describe the genesis and evolution of the data assimilation problem, its impact on the SREF forecasts, and how it could have been detected and adjusted for by the forecaster, including satellite observations and comparisons to radiosonde observations.

Learning objectives

In this case study, the main lessons are:

1. SREF accuracy depends on whether the actual initial condition is captured by the range of perturbed initial atmospheric states.
2. The same methods as used to assess the operational model forecast can be used to assess the SREF members' initial states.
3. It is possible to make adjustments to the ensemble forecast based on corrections to the deficiencies in the ensemble initial states and forecasts.

Credits

by Dr. Bill Bua

Thanks to:

Stephen Jascourt (discussions and review)
Steve Tracton (discussion and review)
Rich Grumm (discussion and review)