The NOAA Hazardous Weather Testbed Experimental Forecast Program (HWT EFP) has conducted annual spring forecasting experiments organized by the Storm Prediction Center (SPC) and National Severe Storms Laboratory (NSSL) since 2000 to test and evaluate emerging scientific concepts and technologies for improved analysis and prediction of hazardous mesoscale weather. A primary goal is to accelerate the transfer of promising new tools from research to operations, through the use of intensive real time experimental forecasting and evaluation activities conducted during the spring and early summer convective storm period, supplemented by post-experiment analyses. There are a wide range of participants each year, including operational forecasters, research scientists, numerical model developers, academic faculty, graduate students, and administrators from numerous national and international organizations. The highly collaborative framework focuses on the application of cutting edge numerical weather prediction systems to address high impact convective weather forecasting challenges. While the experiment has primarily addressed convective scale prediction in the 12-36 hr time frame, the scientific emphasis is aligned closely with the Warn-on-Forecast concept that uses high resolution ensemble prediction systems as a foundation for short term probabilistic forecasts of severe storms.

In recent years, the traditional HWT EFP focus on severe convective storms producing tornadoes, damaging wind gusts, and large hail has been expanded to explore a wider range of convective weather challenges. This has resulted in the establishment of new scientific focus areas to study convective initiation, warm season convective heavy rain, and aviation thunderstorm hazards. The latter two focus areas have been conducted through partnerships with the NCEP Hydrometeorological Prediction Center (HPC) and the NCEP Aviation Weather Center, respectively. Each year, the different forecast and evaluation components operate simultaneously with structured forecast and evaluation activities occurring each day. The weekly participants generally rotate through each component on a daily basis to broaden their understanding and gain unique perspectives on the different thunderstorm forecasting challenges. The experiments also provide opportunities to strengthen collaborations within the convective forecasting communities by identifying shared thunderstorm forecast challenges, and enhance awareness of operational issues related to convective forecast consistency.

The HWT EFP has developed core partnerships with many of the primary numerical modeling centers in the US. In recent years, cutting edge high resolution modeling systems have been contributed by NSSL, the University of Oklahoma's Center for Analysis and Prediction of Storms (CAPS) working with the University of Tennessee National Institute for Computational Sciences, the NOAA/National Centers for Environmental Prediction Environmental Modeling Center (NCEP/EMC), NOAA/Earth System Research Laboratory Global Systems Division (ESRL/GSD), the National Center for Atmospheric Research (NCAR), the Air Force Weather Agency, and the NASA/Short term Prediction Research and Transition Center (SPoRT).

A cornerstone of the experiments since 2007 has been a high resolution Storm Scale Ensemble Forecast (SSEF) system produced by CAPS. This is a multi-model, multi-initial condition, multi-physics system that increased to 50 members in 2011, and is designed to help quantify uncertainty associated with convective-scale predictability and to explore physics sensitivity in convection-allowing modeling. In addition, multiple deterministic convection-allowing WRF forecasting systems configured with 1-4 km grid spacing are run over CONUS geographic areas. All models are initialized at 00 UTC and integrated forward in time to at least 30 hrs; some models were also updated at 12 UTC. The GSD High Resolution Rapid Refresh (HRRR) model run hourly out to 15 hours is being tested for its capability to provide frequent short-term update information on convective storms. Innovative WRF model fields, such as hourly maximum fields of specialized convective storm attributes, simulated satellite imagery and explicit total lightning from microphysics parameters, have been developed as part of the HWT activities. To complement subjective evaluations, traditional and new object-based objective verification measures produced by the Developmental Testbed Center are being utilized to assess their value in convective scale model verification.

By serving as a key facilitator to enhance research-to-operations and operations-to-research dialog, the HWT EFP has provided mutual benefits to the operational and research communities. Highlights that will be discussed include: 1) improvements in convection-allowing model configuration and performance, 2) accelerated transfer of experimental models and unique convective storm fields into operational use, and 3) extensive documentation of the experimental activities and results in the scientific literature.