National Weather Center Colloquium

Using ensemble data assimilation to diagnose flow-specific forecast reliability - illustrated for situations where mesoscale convection is likely to occur over North America

Dr. Mark Rodwell

Scientist
European Centre for Medium-Range Weather Forecasts

10 December 2015, 4:00 PM

National Weather Center, Room 1313
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Weather forecasting is fundamentally a probabilistic task due to the growth of unavoidable initial-state uncertainty. Moreover, the growth rates of these uncertainties can depend on the atmospheric flow, so that predictability may vary from day to day. The established approach to representing uncertainty in probabilistic forecasting is to make an ensemble of forecasts, each starting from a slightly different initial state and including a different realization of model uncertainty. A key question is how to assess the ensemble’s ability to represent the flow-dependent growth of uncertainty. Results suggest that such assessments are not easy to make at the medium range due to complications associated with error propagation and non-linear interactions. Using a specially developed ensemble reliability budget, appropriate for shorter-range assessments within the data assimilation window, these issues can be minimized and flow-dependent deficiencies in representing uncertainty can be identified. An analysis of the reliability budget can also help identify the causes of deficiencies in representing uncertainty. Results are illustrated for a flow situation where mesoscale convection is likely to occur over North America, and which often results in reduced predictive skill for Europe several days later.

Dr. Rodwell obtained his undergraduate degree in Pure Mathematics from Cambridge University and Ph.D. in Meteorology from Reading University where he worked with Brian Hoskins on monsoon dynamics. After that he worked in the UK Met. Office on climate variability (e.g. "Oceanic forcing of the wintertime North Atlantic Oscillation and European climate", with Chris Folland). Currently, he is at the European Centre for Medium-Range Weather Forecasts working on top-down diagnosis of deficiencies within the data-assimilation / forecast systems.

National Weather Center Colloquium Seminar Series website