The Front Range Blizzard of 1990. Part II: Melting Effects in a Convective Band

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  • 1 University of Wyoming, Laramie, Wyoming
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Abstract

A north–south-oriented line of convection, associated with a melting-induced mesoscale front, formed south of the Mile High Radar (MHR) during the early hours of the Front Range blizzard of 6–7 March 1990. The kinematic structure of the mesoscale front, that is, precipitation band, was examined by analyzing single-Doppler radar data from MHR with two analysis techniques. The results from the analyses were augmented and compared with observations from three surface stations within the Winter Icing and Storms Project (WISP) area.

Because of the extraction of the latent heat of fusion from the atmosphere as ice particles melted, the temperature dropped rapidly as the rainband passed. This resulted in a large pool of stable, 0°C air behind the mesoscale front. As the melting continued, this pool expanded toward the east where it was not blocked by terrain. It expanded into a convectively unstable air mass with strong southeasterly winds. A band-parallel low-level jet developed east of the band and remained essentially stationary, while the band propagated beneath and to the east of the jet, at which point the band dissipated. The shallow pool of stable air continued to move slowly to the east.

Abstract

A north–south-oriented line of convection, associated with a melting-induced mesoscale front, formed south of the Mile High Radar (MHR) during the early hours of the Front Range blizzard of 6–7 March 1990. The kinematic structure of the mesoscale front, that is, precipitation band, was examined by analyzing single-Doppler radar data from MHR with two analysis techniques. The results from the analyses were augmented and compared with observations from three surface stations within the Winter Icing and Storms Project (WISP) area.

Because of the extraction of the latent heat of fusion from the atmosphere as ice particles melted, the temperature dropped rapidly as the rainband passed. This resulted in a large pool of stable, 0°C air behind the mesoscale front. As the melting continued, this pool expanded toward the east where it was not blocked by terrain. It expanded into a convectively unstable air mass with strong southeasterly winds. A band-parallel low-level jet developed east of the band and remained essentially stationary, while the band propagated beneath and to the east of the jet, at which point the band dissipated. The shallow pool of stable air continued to move slowly to the east.

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