A Case Study of Cold-season Emergent Orographic Convection and its Impact on Precipitation. Part 2: High-resolution LES Analysis of Convective Cell Evolution and Precipitation Processes.

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Title:	A Case Study of Cold-season Emergent Orographic Convection and its Impact on Precipitation. Part 2: High-resolution LES Analysis of Convective Cell Evolution and Precipitation Processes.
Authors:	Afrifa, Francis O.T.¹ (AUTHOR), Geerts, Bart¹ (AUTHOR) geerts@uwyo.edu, Xue, Lulin² (AUTHOR), Chen, Sisi² (AUTHOR), Hohman, Christopher¹ (AUTHOR), Grasmick, Coltin¹ (AUTHOR), Friedrich, Katja³ (AUTHOR), French, Jeffrey¹ (AUTHOR), Tessendorf, Sarah² (AUTHOR), Zaremba, Troy J.⁴ (AUTHOR), Rauber, Robert M.⁵ (AUTHOR)
Source:	Monthly Weather Review. Jun2026, Vol. 154 Issue 6, p1-22. 22p.
Subjects:	Large eddy simulation models, Meteorological precipitation, Gravity waves, Topography, Heat convection, Winter storms, Snow accumulation
Abstract:	Part 1 of this study demonstrated how terrain-induced gravity waves triggered elevated convection, with tops up to 6 – 7 km above sea level, in a potentially unstable layer during a winter storm event over the Idaho Central Mountains on 7 February 2017. Herein, this case is explored further with a Large Eddy Simulation (LES) at 100 m grid spacing, to examine the detailed structure and evolution of convective cells emergent from shallow stratiform clouds, their interaction with complex terrain, and the resulting precipitation processes. The 100 m LES produced fine-scale precipitation structures similar in depth and width to radar observations, with vertical velocity distributions and cloud microphysical properties matching airborne observations. The 100 m LES confirmed the role of vertically propagating gravity waves over the highest terrain ridges in providing the initial lift necessary to release potential instability. Unlike coarser-resolution simulations, the 100 m LES produced clusters of convective towers, ~2 km wide, roughly matching observations, although they were more regularly spaced than observed. Co-spectral analysis of these towers confirms their convective nature. The small-scale convective updrafts, locally exceeding 2 m s −1 , and mostly within the -10 to -20°C temperature zone, enabled snow particles to grow rapidly through depositional growth and riming, and a significant fraction of the simulated precipitation fell as graupel, according to the LES model. Precipitation from this emergent convection occurred primarily in the lee of the main terrain ridge, on account of the strong flow above mountain top level. Cumulatively, the LES produced 18% more precipitation than non-LES models in this case. [ABSTRACT FROM AUTHOR]
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Database:	Engineering Source

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Abstract:	Part 1 of this study demonstrated how terrain-induced gravity waves triggered elevated convection, with tops up to 6 – 7 km above sea level, in a potentially unstable layer during a winter storm event over the Idaho Central Mountains on 7 February 2017. Herein, this case is explored further with a Large Eddy Simulation (LES) at 100 m grid spacing, to examine the detailed structure and evolution of convective cells emergent from shallow stratiform clouds, their interaction with complex terrain, and the resulting precipitation processes. The 100 m LES produced fine-scale precipitation structures similar in depth and width to radar observations, with vertical velocity distributions and cloud microphysical properties matching airborne observations. The 100 m LES confirmed the role of vertically propagating gravity waves over the highest terrain ridges in providing the initial lift necessary to release potential instability. Unlike coarser-resolution simulations, the 100 m LES produced clusters of convective towers, ~2 km wide, roughly matching observations, although they were more regularly spaced than observed. Co-spectral analysis of these towers confirms their convective nature. The small-scale convective updrafts, locally exceeding 2 m s −1 , and mostly within the -10 to -20°C temperature zone, enabled snow particles to grow rapidly through depositional growth and riming, and a significant fraction of the simulated precipitation fell as graupel, according to the LES model. Precipitation from this emergent convection occurred primarily in the lee of the main terrain ridge, on account of the strong flow above mountain top level. Cumulatively, the LES produced 18% more precipitation than non-LES models in this case. [ABSTRACT FROM AUTHOR]
ISSN:	00270644
DOI:	10.1175/MWR-D-25-0157.1