Lagrangian Analyses of Rainfall Structure and Evolution for Organized Thunderstorm Systems in the Urban Corridor of the Northeastern United States

Abstract

In this study, a climatology of the structure and evolution of rainfall for organized thunderstorm systems in the urban corridor of the northeastern United States is developed. These storm systems are major agents of flash flooding for urban regions of the northeastern United States and, more generally, for the United States east of the Rocky Mountains. The analyses are motivated by problems that center on characterizing flash flood hazards. The authors focus on spatial heterogeneities of rainfall associated with urbanization in a region of complex landscape including mountainous terrain and land-water boundaries along the geometrically complex coastline of the New York City-New Jersey metropolitan region. The sample of storms selected for investigation consists of the 50 days from April to September 2001-09 with the largest cloud-to-ground lightning flash density derived from National Lightning Detection Network (NLDN) observations over the study region. Storm-tracking analyses of 3D radar reflectivity fields are performed for the 50 storm days and used to develop a Lagrangian climatology of storm structure and evolution for the study region. Rainfall analyses for the 50 storm days are based on high-resolution (1 km, 15 min) bias-corrected radar rainfall fields developed from the Hydro-NEXRAD system. The analyses suggest that complex terrain and land-water boundaries have large impacts on Lagrangian storm properties. Areas of increased heavy rainfall and lightning flash density over New York City were identified. The authors found evidence for changing storm structure as thunderstorms pass over New York City, but little evidence that thunderstorms split as they approach New York City.

Flash flooding in small urban watersheds: Storm event hydrologic response

“…There were 57 flood peaks in Harry's Brook exceeding 1 m 3 s −1 during the 2 year observation period and 48 events with a unit discharge (i.e., flood peak discharge divided by drainage area) exceeding 1 m 3 s −1 km −2 , placing Harry's Brook among the “flashiest” watersheds in the U.S. [ Smith and Smith , ]. Flood events are concentrated during the warm season; warm‐season thunderstorms are the main agents for flash flooding in Harry's Brook, as in urban watersheds for much of the U.S. east of the Rocky Mountains [ Smith et al ., ; Ntelekos et al ., ; Smith and Smith , ; Yang et al ., ; Yeung et al ., ]. Ten events in Harry's Brook had values of peak discharge exceeding 8.6 m 3 s −1 (unit discharge of 7.8 m 3 s −1 km −2 , see Table ).…”

Spatial Analysis of High-Resolution Radar Rainfall and Citizen-Reported Flash Flood Data in Ultra-Urban New York City

“…Yeung used high-resolution radar rainfall fields from the Fort Dix (New Jersey) radar, where weather surveillance radar (WRF)-modeled storm events were used to investigate the role of urban areas on convective storm tracks in the greater NYC region. The results showed an increased number of days exceeding 25 mm of rainfall over New York City (averaging nine per summer season [27]). Recently, Stage-IV rainfall data were used to classify rainfall in New York City down to 1-h events [28].…”

An idealized LES study of urban modification of moist convection

“…() investigated the 22–23 July 2010 heavy convective precipitation event in the Milwaukee, Wisconsin metropolitan region and concluded that urbanization had little effect on the vertical dynamics of the precipitating cloud system. Many other similar studies have been conducted around the world as reviewed elsewhere (Shepherd, ; Pielke et al ., ; Mahmood et al ., ; Zhang et al ., ; Yeung et al ., ; Nie et al ., ). All of these studies suggested strong connections between urban areas, convection enhancement, and increased precipitation.…”