2026/06/24 by Stephen R. Guimond
Earth and Planetary Sciences · Environmental Science · #Tropical and Extratropical Cyclones Research #Meteorological Phenomena and Simulations #Climate variability and models
paper · doi:10.1175/jas-d-25-0180.1
Abstract This paper investigates the dynamics governing multibanded cloud and precipitation structures in extratropical cyclones through a case study from the NASA Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign. On 1 February 2020, a low pressure system emerged off the North Carolina coast at 1200 UTC, deepening by 7 hPa in 6 h as it accelerated northeast over the Atlantic. High-resolution Geostationary Operational Environmental Satellite (GOES) visible imagery revealed multiple bands of high-reflectance cloud to the north/northeast of the center, along with clusters of convective cells closer to the core. Wavelet analysis identified a dominant multiband wavelength of 30 km and a secondary peak at 15–20 km. Airborne radar measurements from IMPACTS flights showed deep convection near the center and narrow, elevated reflectivity bands linked to the multiband features farther out. Numerical simulations reproduced the multibands, enabling exploration of their dynamical origin. Intrinsic phase speed and polarization relation calculations revealed that, contrary to several previous studies, the dominant multibands were not gravity waves. Instead, the bands were identified as manifestations of inflection-point instability due to the presence of counterrotating secondary circulations and the vertical wind shear profile with low Richardson numbers near the upper-level outflow. Gravity waves were present in the low- to midlevels generated by convection, but they did not account for the strong perturbations in the mid–upper levels. These new scientific insights into the governing dynamics of multibanded structures in extratropical cyclones highlight the role of shear-driven hydrodynamic instabilities. Significance Statement Extratropical cyclones along the U.S. East Coast can produce intense bands of snow and other types of precipitation that cause travel chaos and potential loss of life. In this work, a storm of this type was studied using NASA aircraft and satellite data as well as computer simulations. The results show that the storm bands were not caused by atmospheric waves, as scientists often thought, but by sharp changes in the wind speed with height called shear. This shear created unstable layers that rolled and mixed the air, forming organized cloud and precipitation patterns. Understanding these fundamental physical processes can help forecasters better predict when and where heavy snowbands will form, improving warnings and securing public safety.