The climate of the Great Plains is dominated by mesoscale convective systems (MCS), which supply a significant portion of warm season rainfall and are responsible for severe weather and flooding across the region. However, little is known about past behavior and long-term drivers of these systems, limiting our ability to predict future changes in hydroclimate and extreme weather for much of the central US. Here, we generate a new record of past MCS activity and hydroclimate variability from central Texas and compare it against the results of transient climate model simulations to understand the underlying causes of past changes in extreme weather and climate in the central US. We find that changes in storm activity and hydroclimate in the southern Great Plains over the last the 20,000 years were dominated by changes in the strength of the Great Plains Low Level Jet, driven by springtime land surface temperature changes. These results suggest that a similar dynamical response to future warming will lead to enhanced MCS activity and an increase in extreme weather and flooding across the southern and central Great Plains in the future.