SPC Evaluation: Steve Weiss Part 3

• Since late 2006, SPC has had access to a real-time 4 km version of the ARW that is run once daily at NSSL.  SPC forecasters have been using both models in their severe forecasting mission, and have identified various strengths and weaknesses with both models but have learned how to use these performance characteristics to their advantage.  For example, the NMM appears to display a high convective storm/precipitation bias whereas the most recent ARW versions have a slight low bias.  Of course, the convection-allowing WRF models are relatively early in their development and considerable work remains, such as improving physics and development of cutting-edge data assimilation systems that are specifically designed for high resolution models with grid lengths < 4 km.  But we have also seen considerable evidence during the last three years that operational severe weather forecasters at SPC have benefited from the daily availability of the WRF-NMM4 output, and more recently WRF-ARW4 output, and these benefits are reflected in improved SPC forecast products on important severe weather days.  [See the attached powerpoint file entitled “WRF-NMM and WRF-ARW Use at SPC”, which was part of a presentation given at the 2007 AMS WAF/NWP Conference in June]. Furthermore, the increasing number of WFOs running local experimental limited-area WRF models and viewing the WRF-NMM4 online web page strongly suggests that local forecasters believe there are advantages to having routine access to operational high resolution model output.