Spatiotemporal Characteristics and Large-Scale Environments of Mesoscale Convective Systems East of the Rocky Mountains

Abstract

The spatiotemporal variability and three-dimensional structures of mesoscale convective systems (MCSs) east of the U.S. Rocky Mountains and their large-scale environments are characterized across all seasons using 13 years of high-resolution radar and satellite observations. Long-lived and intense MCSs account for over 50% of warm season precipitation in the Great Plains and over 40% of cold season precipitation in the southeast. The Great Plains has the strongest MCS seasonal cycle peaking in May–June, whereas in the U.S. southeast MCSs occur year-round. Distinctly different large-scale environments across the seasons have significant impacts on the structure of MCSs. Spring and fall MCSs commonly initiate under strong baroclinic forcing and favorable thermodynamic environments. MCS genesis frequently occurs in the Great Plains near sunset, although convection is not always surface based. Spring MCSs feature both large and deep convection, with a large stratiform rain area and high volume of rainfall. In contrast, summer MCSs often initiate under weak baroclinic forcing, featuring a high pressure ridge with weak low-level convergence acting on the warm, humid air associated with the low-level jet. MCS genesis concentrates east of the Rocky Mountain Front Range and near the southeast coast in the afternoon. The strongest MCS diurnal cycle amplitude extends from the foothills of the Rocky Mountains to the Great Plains. Summer MCSs have the largest and deepest convective features, the smallest stratiform rain area, and the lowest rainfall volume. Last, winter MCSs are characterized by the strongest baroclinic forcing and the largest MCS precipitation features over the southeast. Implications of the findings for climate modeling are discussed.

Observed Warm‐Season Characteristics of MCS and Non‐MCS Rainfall and Their Recent Changes in the Central United States

“…Similar results obtained using the NLDAS and Stage IV precipitation datasets and agreement of the MCS rainfall characteristics with those discussed in previous studies (e.g., Feng et al, 2019;Nesbitt & Zipser, 2003;Song et al, 2019) lend confidence to our conclusions. Although the trends examined here are based on data from only 22 years, our findings align well with projected changes in precipitation in a warming climate-precipitation becomes more extreme and more variable.…”

Updraft and Downdraft Core Size and Intensity as Revealed by Radar Wind Profilers: MCS Observations and Idealized Model Comparisons

“…Although we limit our examples to the mature stages in the MCS lifecycle, any lifecycle assessment based on the presence of key radar squall‐line precipitation properties is nonetheless nontrivial to generalize. Moreover, we anticipate that mature MCS transition from updraft‐dominant to downdraft‐dominant phases, for example, as reflected by changes in mature‐stage convective and stratiform precipitation coverage (e.g., Feng et al, 2019). Thus, the authors recommend caution when interpreting the mature‐stage results that follow.…”

Can the Multiscale Modeling Framework (MMF) Simulate the MCS‐Associated Precipitation Over the Central United States?

“…Previous studies show that the MMF with the coarse host‐GCM grid is able to capture MCSs in the Tropics (Tao & Chern, ; Randall et al, ). However, our study shows the MMF model has difficulty in simulating MCS‐associated precipitation in midlatitude continental conditions during spring where most MCSs were supported by strong baroclinic forcing (Feng et al, ; Song et al, ). The different model behaviors reflect the different mechanisms driving the MCSs between tropical and midlatitude regions.…”

“…Investigating how resolving topography variations within the CRM domains would help the MMF model simulate MCSs can be an interesting future work. Further, summer MCSs in this region often occur under weak baroclinic forcing with favorable thermodynamic environments (Feng et al, ; Song et al, ). Future work similar to this study is needed to examine how well the MMF can simulate observed summer MCSs.…”

“…Rainfall from mesoscale convective systems (MCSs) contributes up to 70% of warm season precipitation in the central United States (Fritsch et al, ; Laing & Fritsch, ; Haberlie & Ashley, ; Feng et al, ), and they often lead to dangerous flash flooding (Schumacher & Johnson, ; Stevenson & Schumacher, ). In addition, more frequent and stronger long‐lived MCSs have been found to be responsible for the increasing trend in springtime total and extreme rainfall in the central United States over recent decades (Feng et al, ).…”