Corridors of Warm Season Precipitation in the Central United States

Abstract

During the warm season in the central United States there often exists a corridor of precipitation where a succession of mesoscale convective systems (MCSs) follow similar paths lasting several days. The total cumulative rainfall within a corridor can be substantial while precipitation at nearby regions may be below normal. Understanding the nature of the corridors and the environmental factors important for their formation thus has important implications for quantitative precipitation forecasting and hydrological studies. In this study a U.S. national composite radar dataset and model-analyzed fields are used for the 1998–2002 warm seasons (July–August) to understand the properties of corridors and what environmental factors are important for determining when and where they develop. The analysis is restricted to a relatively narrow longitudinal band in the central United States (95°–100°W), a region where convection often intensifies and becomes highly organized. It is found that ∼68% of MCSs were members of a series and that corridors typically persist for 2–7 days with an extreme case lasting 13 days. Cumulative radar-derived maximum rainfall ranges from 8 to 50 cm, underscoring the fact that corridors can experience excessive rainfall. Combining radar with Rapid Update Cycle model kinematic and thermodynamic fields, 5-yr composites are presented and stratified according to the environmental conditions. While the corridors show the expected association with areas of enhanced CAPE and relatively strong northwesterly/westerly shear, the strongest association is with the northern terminus region of the nocturnal low-level jet (LLJ). Furthermore, the relative intensity of the rainfall is positively correlated with the strength of the LLJ. The LLJ is thought to play a role through enhanced convergence and lifting, moisture transport, and frontogenesis. In the five years analyzed, the large-scale environment varied considerably, but the role of the LLJ in the formation of corridors remained persistent.

A Comparison of Precipitation Forecast Skill between Small Convection-Allowing and Large Convection-Parameterizing Ensembles

“…Thus, the primary rainfall axes are more representative of all 23 cases than the secondary axes. The primary rainfall axis is similar to that observed in studies examining longer time periods (e.g., Carbone et al 2002;Tuttle et al 2006), while the secondary axis has not been observed in the studies examining the longer time periods. However, Clark et al (2007) did observe a secondary rainfall axis during Feb -Apr 2007 over the northern portion of the central US.…”

Comparison of the Diurnal Precipitation Cycle in Convection-Resolving and Non-Convection-Resolving Mesoscale Models

“…The latitude 38°N was chosen to separate the domain into two halves because the corridor in which propagating rainfall systems occurred most frequently was roughly the northern half of the full domain. The tendency for propagating systems to concentrate in latitudinal corridors has been documented by Tuttle and Davis (2006). This partitioning led to diurnally averaged Hovmöller diagrams of observed rainfall with the propagating (nonpropagating) rainfall axis having the higher amplitude in the northern (southern) portion of the analysis domain.…”

Analysis of a Destructive Wind Storm on 16 November 2008 in Brisbane, Australia

“…At least observationally this includes the pursuit of a better understanding of storm environmental attributes that are characteristic of high-end wind storms. Coniglio et al (2011) found that the primary difference between the 8 May 2009 derecho environment and a more general mesoscale convective system (MCS; Houze 2004) environment was a strong and deep lowlevel jet (Tuttle and Davis 2006) that was transporting anomalously high mixing ratio air toward the storm underneath anomalously large midtropospheric lapse rates. Interestingly, these ingredients are primarily promoting stronger updrafts, rather than stronger downdrafts.…”