Observations of freezing drizzle in extratropical cyclonic storms during IMPROVE-2

Observations of supercooled drizzle aloft within two storms impacting the Oregon Cascades during the second Improvement Microphysical Parameterization through Observational Verification Experiment IMPROVE-2) field project are presented. The storms were characterized by a structure and evolution similar to the split-front model of synoptic storms. Both storms were also characterized by strong cross-barrier flow. An analysis of aircraft and radar data indicated the presence of supercooled drizzle during two distinct storm periods: 1) the intrafrontal period immediately following the passage of an upper cold front and 2) the postfrontal period. The conditions associated with these regions of supercooled drizzle included 1) temperatures between -3° and -19°C, 2) ice crystal concentrations between 1 and 2 L⁻¹, and 3) bimodal cloud droplet distributions of low concentration [cloud condensation nuclei (CCN) concentration between 20 and 30 cm⁻³ and cloud drop concentration <35 cm⁻³].Unique to this study was the relatively cold cloud top (15 dBZ) in this region, the relatively high condensate supply rate led to hazardous icing conditions. The current study reveals that vertical motions generated by local topographic features are critical in precipitation processes such as drizzle formation and thus it is essential that microphysical models predict these motions.

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Author Ikeda, Kyoko
Rasmussen, Roy M.
Hall, William D.
Thompson, Gregory
Publisher UCAR/NCAR - Library
Publication Date 2007-09-01T00:00:00
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Topic Category geoscientificInformation
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Metadata Date 2025-07-17T17:00:40.973840
Metadata Record Identifier edu.ucar.opensky::articles:6955
Metadata Language eng; USA
Suggested Citation Ikeda, Kyoko, Rasmussen, Roy M., Hall, William D., Thompson, Gregory. (2007). Observations of freezing drizzle in extratropical cyclonic storms during IMPROVE-2. UCAR/NCAR - Library. https://n2t.org/ark:/85065/d7rf5v88. Accessed 30 July 2025.

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