National Weather Service United States Department of Commerce

Overview

The STI Modeling Program Team is responsible for supporting a variety of NWS modeling and research initiatives to improve weather forecasts. This is accomplished by funding research and education projects to accelerate and advance the development of new models, and foster collaboration among NOAA research scientists, federal labs, operational forecasters and the academic community. Examples of programs managed by this program division include efforts to improve guidance for hurricane track, intensity, and storm surge forecasts; develop an end-to-end air quality forecast capability; advance research to extend forecast skill beyond 8-10 days; and implement a weather-scale, fully-coupled numerical weather prediction system.

 

STI Modeling Program Seminar, The stratiform region of squall lines and its representation in convection-allowing numerical models by George H. Bryan (NCAR) occurred on June 14, 2017 

Abstract: The stratiform region of a squall line is the mesoscale area of relatively low radar reflectivity (20-40 dBZ) that often develops near the more-intense convective region (40-60 dBZ). Real-time numerical models that explicitly represent convection (with grid spacing of ~3 km) often fail to produce stratiform regions. This talk focuses on some microphysical and dynamical processes that can improve the structure of the stratiform region in such models. A key microphysical process is the inclusion of a fast-falling frozen hydrometeor (i.e., hail), which is primarily associated with the high-reflectivity convective region, but allows for the production of slower-falling snow aloft which ultimately forms the stratiform region. Turbulent mixing processes also play a key role, as revealed by high-resolution simulations (with grid spacing ~100 m) that show how air in stratiform regions has a history of mixing between mid-level and boundary-layer air. Identical simulations with relatively coarser resolution (grid spacing ~1 km) show practically no mixing and, consequently, inaccurate humidity profiles. In summary, stratiform regions are produced by a combination of microphysical and dynamical processes, and thus efforts to improve convection-resolving models need to address both processes.

 

 

 

 

 

 

 

 

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