Ice storms are among the most hazardous, disruptive, and costly meteorological phenomena in the northeastern United States. The accretion of freezing rain during ice storms endangers human safety, compromises public infrastructure, and causes economic losses on local and regional scales. Furthermore, ice storms present a major operational forecast challenge due to the combined influence of synoptic, mesoscale, and microphysical processes on precipitation type. In consideration of these socioeconomic impacts and forecast issues, we have identified three primary objectives for this thesis: 1) create long-term climatologies of freezing rain and ice storms in the northeastern U.S., 2) identify antecedent environments conducive to ice storms and dynamical mechanisms responsible for freezing rain, and 3) increase situational awareness of the synoptic and mesoscale processes that govern the evolution of ice storms.
The climatology portion of this thesis examines the temporal and spatial variability of freezing rain and ice storms during the 1975–2010 and 1993–2010 periods, respectively. Individual ice storms are also partitioned by five characteristic synoptic-scale weather patterns. Synoptic composite maps for the two most common event types (Type G and Type BC) illustrate how large-scale circulation patterns and associated quasi-geostrophic (QG) forcing, thermal boundaries, and moisture transport establish environments favorable for freezing rain. Composite cross sections also offer critical insights into synoptic–mesoscale linkages that influence the duration and intensity of freezing rain. The composite analysis for both event types suggests that ice storms occur in association with QG ascent and low-level frontogenetical forcing beneath the equatorward entrance region of an upper-level jet. Moreover, low- to midlevel warm advection and moisture transport, in conjunction with near-surface ageostrophic cold advection on the poleward side of a surface warm front, helps prolong freezing rain events by maintaining a thermodynamic profile conducive to freezing rain.
Case studies of the 3–4 Jan 1999 (Type G) and 11–12 Dec 2008 (Type BC) ice storms investigate the synoptic evolution of each event and describe the physical mechanisms that prolonged the duration of freezing rain and resulted in significant ice accretions. These case studies not only reinforce the results of the composite analyses, but also demonstrate how mesoscale processes such as terrain–flow interactions and frontogenesis modify synoptic-scale circulations and thermodynamic environments on regional and local scales. Based on our findings from the composite and case study analyses, we propose conceptual models illustrating the key synoptic ingredients and dynamical processes associated with Type G and Type BC ice storms.
|Advisor:||Bosart, Lance F., Keyser, Daniel|
|School:||State University of New York at Albany|
|Department:||Earth and Atmospheric Sciences-Athmospheric Science|
|School Location:||United States -- New York|
|Source:||MAI 51/04M(E), Masters Abstracts International|
|Keywords:||Freezing rain, Ice storms, Mesoscale meteorology, Synoptic meteorology, United States|
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