Characteristics of major ice storms in the central United States

Abstract

A 30-yr (1979–2009) climatology of major ice storms with 19.05 mm (0.75 in) ice accumulation or greater across the central United States is presented. An examination of the United States Army Cold Regions Research and Engineering Laboratory Ice Storm Database, in conjunction with National Climatic Data Center Storm Data, revealed 20 (out of 51) ice storms during the period which satisfied the selection criteria herein. Using the General Meteorological Package with the North American Regional Reanalysis dataset, system-relative composites using both traditional (i.e., mean) and probabilistic (i.e., frequency analysis of median, quartiles, and threshold exceedance) composite-analysis measures for the major ice storms were created. The composite analysis was computed at start, maximum coverage, and end times to depict the evolution of features used to diagnose the synoptic and mesoscale environment potentially favorable for major ice storms within the central United States. At the maximum-coverage time, the composite analysis indicates the presence of sub-freezing surface temperatures to the north of a southwest-to-northeast oriented quasi-stationary front below a strong 850-hPa jet streak. The low-level jet streak bisects the quasi-stationary front and is enhanced by the direct thermal circulation associated with an upper-level jet streak. These features are responsible for supplying warm and moist air into the elevated warm layer, which provides an environment to completely melt frozen precipitation. An upper-level long-wave trough is anchored over the southwestern United States and there is some evidence that it leads to short-wave troughs ejecting into the plains. These troughs may be responsible for multiple rounds of enhanced vertical motion, precipitation, and freezing rain. Finally, an analysis of probabilistic measures of the 300- and 850-hPa jet streaks and elevated warm-layer characteristics indicates the importance of these fields in major ice storms in this region.