Contrasting spring and summer large-scale environments associated with mesoscale convective systems over the U.S. Great Plains

Journal Article · Tue Oct 01 00:00:00 EDT 2019 · Journal of Climate

DOI:https://doi.org/10.1175/JCLI-D-18-0839.1· OSTI ID:1575396

Song, Fengfei ^[1]; Feng, Zhe  ^[1]; Leung, Lai-Yung  ^[1]; Houze, Robert A. ^[2]; Wang, Jingyu ^[1]; Hardin, Joseph C.  ^[1]; Homeyer, Cameron R. ^[3]

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1. BATTELLE (PACIFIC NW LAB)
2. UNIVERSITY OF WASHINGTON (MAIN CAMPUS)
3. University of Oklahoma

Mesoscale convective systems (MCSs) are frequently observed over the U.S. Great Plains during boreal spring and summer. Here, four types of synoptically-favorable environments for spring MCSs and two types of synoptically- favorable and unfavorable environments for summer MCSs are identified using self-organizing maps (SOM) with the inputs of observational data. During spring, frontal systems providing a lifting mechanism and an enhanced Great Plains low-level jet (GPLLJ) providing anomalous moisture are important features identified by SOM analysis as they create favorable dynamical and thermodynamic environments for MCS development. During summer, the composite MCS environment shows small positive convective available potential energy (CAPE) and convective inhibition (CIN) anomalies, which are in stark contrast with the large positive CAPE and negative CIN anomalies in spring. This contrast suggests that convection may occur even within weak dynamical and thermodynamic perturbations in summer so that MCSs may be inherently less predictable in summer. The two synoptically-favorable environments identified in summer have frontal characteristics and an enhanced GPLLJ, but both shift north compared to spring. The two synoptically-unfavorable environments feature enhanced upper-level ridges, but differ in the strength of the GPLLJ. In both seasons, MCS precipitation amount, area and rate are much larger in the frontal-related MCSs than non-frontal MCSs. A large-scale index constructed using the pattern correlation between the large-scale environment and the synoptically-favorable SOM types is found to be skillful for predicting MCS number, precipitation rate and area in spring, but its explanatory power decreases significantly in summer. The low predictability of summer MCSs deserves further investigation in the future.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1575396
• Report Number(s): PNNL-SA-140340
• Journal Information: Journal of Climate, Vol. 32, Issue 20
• Country of Publication: United States
• Language: English