Document Type

Article

Publication Date

11-1-2014

Abstract

Data from airborne W-band radar, thermodynamic fields from the Weather Research and Forecasting (WRF) Model, and air parcel back trajectories from the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model are used to investigate the finescale reflectivity, vertical motion, and airmass structure of the comma head of a winter cyclone that produced 15–25 cm of snow across the U.S. Midwest on 29–30 January 2010. The comma head consisted of three vertically stacked air masses: from bottom to top, an arctic air mass of Canadian origin, a moist cloud-bearing air mass of Gulf of Mexico origin, and a drier air mass originating mostly at low altitudes over Baja California and the Mexican Plateau. The drier air mass capped the entire comma head and significantly influenced precipitation distribution and type across the storm, limiting cloud depth on the warm side, and creating instability with respect to ice-saturated ascent, cloud-top generating cells, and a seeder–feeder process on the cold side. Convective generating cells with depths of 1.5–3.0 km and vertical air velocities of 1–3 m s−1 were ubiquitous atop the cold side of the comma head. The airmass boundaries within the comma head lacked the thermal contrast commonly observed along fronts in other sectors of extratropical cyclones. The boundary between the Gulf and Canadian air masses, although quite distinct in terms of precipitation distribution, wind, and moisture, was marked by almost no horizontal thermal contrast at the time of observation. The higher-altitude airmass boundary between the Gulf of Mexico and Baja air masses also lacked thermal contrast, with the less-stable Baja air mass overriding the stable Gulf of Mexico air.

DOI

10.1175/MWR-D-14-00057.1

Comments

© Copyright 2014 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act September 2010 Page 2 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyrights@ametsoc.org.

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