Weakly Forced Thunderstorms in the Southeast US Are Stronger Near Urban Areas

While cities are well documented to enhance precipitation through the urban rainfall effect (URE), the distinguishing characteristics of urban‐influenced storms that help establish the URE are poorly understood. The purpose of this study is to examine the morphological traits (i.e., size, duration, intensity, etc.) and near‐storm environmental conditions of weakly forced thunderstorms (WFTs) occurring near urban areas in the Southeast US relative to storms forming in surrounding rural areas. Urban WFTs are found to have higher reflectivities, are more likely to contain hail, and produce more lightning than nearby non‐urban storms, but their sizes and shapes are statistically indistinguishable. When disaggregated across individual urban areas, the increase in maximum composite reflectivity among urban storms is the most pervasive morphological difference, with 24 of the 31 cities displaying elevated reflectivities. Urban WFTs also benefit from near‐storm environments with greater instability and higher precipitation efficiency, which may further contribute to the URE. Plain Language Summary Research has shown that cities can generate extra precipitation in areas downwind, but the exact causes for the extra rainfall have not been definitively established. While cities can cause additional thunderstorms, they may also cause thunderstorms to look, move, or grow differently, ultimately leading to the precipitation boost. In this study, we find that weakly forced thunderstorms forming closest to cities are stronger, more hail‐prone, and bigger lightning‐producers than otherwise similar storms forming outside the city. Key Points Weakly forced thunderstorms near cities are associated with higher composite reflectivities than storms in adjacent outlying areas Total lightning flash density and radar‐based hail indicators are also larger among storms forming closer to the urban centers Urban storms formed in environments with greater instability and higher precipitable water than nearby non‐urban storms