Observed and Projected Changes of Large‐Scale Environments Conducive to Spring MCS Initiation Over the US Great Plains.

Mesoscale convective systems (MCSs) are frequent over the US Great Plains during spring. The link between large‐scale environments and spring MCS initiation were well established. Here, historical and future changes of spring large‐scale environments favorable for MCS initiation are investigated using an MCS tracking data set, ERA5 reanalysis, and 20 Coupled Model Intercomparison Project Phase 6 (CMIP6) models. The frequency of Great Plains low‐level jet (GPLLJ)‐related MCS environments is found to have increased by ∼41% from 1979 to 2019, consistent with the enhanced GPLLJ and more frequent MCSs. Comparing CMIP6 AMIP and historical experiments, we find that the observed GPLLJ strengthening and more frequent MCS environments are mainly due to the decadal sea‐surface temperature variations rather than external forcings. Under a high emission scenario, the frequency of GPLLJ‐related environments favorable for MCS initiation will increase by ～65% during 2015–2100, along with a stronger GPLLJ, suggesting more frequent MCSs over the US Great Plains in a warming world. Plain Language Summary: Convective storm systems that extend over several hundred kilometers are frequently observed and contribute to a majority of the warm season rainfall over the US Great Plains. It is a major challenge for climate models to simulate these storms because the processes governing their initiation and evolution are not well resolved. However, large‐scale atmospheric circulations such as the Great Plains low‐level jet (GPLLJ) that provide favorable environments for these storms in spring are well observed and simulated by climate models. Therefore, the GPLLJ may be used to understand past and future changes of these storms. Here, we found GPLLJ‐related environments become more frequent from 1979 to 2019, related to the observed strengthening of the GPLLJ. To determine whether these changes are due to global warming, we compare simulations driven by the observed sea‐surface temperature variation with simulations driven only by anthropogenic forcing. The results suggest that the observed GPLLJ strengthening is mainly due to the natural decadal variation of sea‐surface temperature. However, with continued warming under a high greenhouse gas emission scenario, the GPLLJ is greatly enhanced during 2015–2100. Accompanied by more frequent occurrence of the GPLLJ‐related environments, the frequency of large convective systems may also increase in the future. Key Points: Low‐level jet‐related mesoscale convective system environments in spring over the US Great Plains became more frequent from 1979 to 2019The more frequent convection environments are a response to decadal sea‐surface temperature variation rather than to external forcingAlong with the enhanced low‐level jet under a high emission scenario, the low‐level jet‐related storm environment will become more frequent [ABSTRACT FROM AUTHOR]