A regional climate model forced by a GCM control climate and a transient GHG scenario climate is used to study the importance of mesoscale processes to the climate change in the continental U.S. The projected warming in the scenario climate over the central U.S. is significantly suppressed in summer compared with surrounding regions, resulting in a warming "hole". The diagnoses of simulated climates suggest that the hole is likely caused by a series of mesoscale atmospheric and hydrological processes unique to the region. A dipole-structured low-level jet frequency change (decrease to the north and increase to the south) first initiates the increased convergence and mesoscale convective systems in late spring/early summer. Then the increased cloudiness and precipitation recharge soil moisture storage in mid-summer when intensively cultivated crops extract water from the root zone. The suppressed sensible heat flux accompanied with excessive evapotranspiration from wet surface results in the warming hole in middle/late summer. This trend of less warming (or even slight cooling) has been occurring in the central U.S. during the last quarter of the 20th century even when the global warming was evident.