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Abstract Flash flooding in the arid/semiarid southwestern United States is frequently associated with convective rainfall during the North American monsoon. In this study, we examine flood-producing storms in central Arizona based on analyses of dense rain gauge observations and stream gauging records as well as North American Regional Reanalysis fields. Our storm catalog consists of 102 storm events during the period of 1988–2014. Synoptic conditions for flood-producing storms are characterized based on principal component analyses. Four dominant synoptic modes are identified, with the first two modes explaining approximately 50% of the variance of the 500-hPa geopotential height. The transitional synoptic pattern from the North American monsoon regime to midlatitude systems is a critical large-scale feature for extreme rainfall and flooding in central Arizona. Contrasting spatial rainfall organizations and storm environment under the four synoptic modes highlights the role of interactions among synoptic conditions, mesoscale processes, and complex terrains in determining space–time variability of convective activities and flash flood hazards in central Arizona. We characterize structure and evolution properties of flood-producing storms based on storm tracking algorithms and 3D radar reflectivity. Fast-moving storm elements can be important ingredients for flash floods in the arid/semiarid southwestern United States. Contrasting storm properties for cloudburst storms highlight the wide spectrum of convective intensities for extreme rain rates in the arid/semiarid southwestern United States and exhibit comparable vertical structures to their counterparts in the eastern United States.
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This content will become publicly available on September 1, 2026
Temporal and Spatial Analysis of Freezing Rain Regimes over Eastern North America
Freezing rain events, which have caused billions of dollars in damage in recent decades, are still one of the least understood forms of precipitation. These events affect both urban and rural regions, including cities and forests. However, the often short-lived and sporadic occurrence of these events poses significant challenges to accurate reporting, complicating analysis attempting to fill this knowledge gap. Through the utilization of ERA5 reanalysis from 1979 to 2020 as a proxy for lacking ground truth data, freezing rain events were identified and analyzed throughout eastern North America. These events were then sorted into full area and subarea regimes through a multivariate self-organizing map (SOM) analysis. This classification of regimes and their subsequent analysis showed the varying importances of the initial synoptic states of each event and provide examples of distinct synoptic structures associated with freezing rain events impacting different regions of eastern North America. In addition, our regime classification identified the prevalence of extreme events associated with each regime. This SOM approach can also be configured to more regional scales to provide more granularity to specific regions of eastern North America.
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- Award ID(s):
- 2110243
- PAR ID:
- 10635610
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Applied Meteorology and Climatology
- Volume:
- 64
- Issue:
- 9
- ISSN:
- 1558-8424
- Page Range / eLocation ID:
- 1177 to 1190
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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