METROMEX redux: Is its urban precipitation maximum downwind enhancement or lateral maxima from storm bifurcation?

The current effort provides an historical review of the literature on urban impacts on summer convective precipitation (PP). It then summarized the methods used in such analyses and recommended methodological techniques that provide insights into interactions between urban, synoptic, topographic, and coastal thermodynamic processes that produce the variety of observed and modeled PP impacts. It then discussed studies that have provided new insights into these processes. The review finally reevaluated the classic METROMEX urban downwind PP maximum, in light of the newer observations of urban-induced thunderstorm (TS) bifurcation. Two science questions addressed included: (i) what are the best practices to better understand the relevant urban impacts on resultant summer TS PP patterns and (ii) can the METROMEX observed downwind urban PP maximum be reconciled with the newer observed urban TS bifurcation effect? 

The most significant results from this reanalysis of the “classic” METROMEX plot of total summer TS rainfall has revealed that: (i) its downwind maximum can be revisualized to show two downwind bifurcated lateral PP maxima and (ii) the original results included storms from all directions, and thus the individual twin bifurcations PP maxima seemingly blended into a single contiguous downwind maximum. Less-cited original METROMEX analyses reproduced herein did in fact show that the original study showed: (i) a diurnal late afternoon PP peak associated with UHI initiation over the city and (ii) that the predominant NNE moving storms did produce a clearly bifurcated downwind maxima. These expanded results now are consistent with the newer results discussed in the paper.