While land surface feedbacks are certainly playing a role, we recently reinvestigated this issue and found that ocean-atmosphere interactions can also force this area of cooling:
Eischeid, J.K., M.P. Hoerling, X.-W. Quan, A. Kumar, J. Barsugli, Z.M. Labe, K.E. Kunkel, C.J. Schreck III, D.R. Easterling, T. Zhang, J. Uehling, and X. Zhang (2023). Why has the summertime central U.S. warming hole not disappeared? Journal of Climate, DOI:10.1175/JCLI-D-22-0716.1 https://journals.ametsoc.org/view/journals/clim/aop/JCLI-D-22-0716.1/JCLI-D-22-0716.1.xml