The East Asian Summer Monsoon (EASM) is characterized by distinct intraseasonal stages – pre-mei-yu, mei-yu, and midsummer – and with abrupt northward jumps in between. Observations have suggested close connections between the seasonal transitions of the EASM and the northward migration of the westerlies impinging on the Tibetan Plateau. The causal relationship and the underlying dynamical processes between the two, however, remain elusive. A recent hypothesis argues that past changes of the East Asian summer climate were caused by changes to the timing and duration of the intraseasonal stages of the EASM; these rain stages were in turn controlled by changes to the meridional position of the westerlies impinging on the Tibetan Plateau. In this talk, I will first briefly introduce tests of this hypothesis in the context of the simulated Holocene climate and observed modern day interannual variability. I will then present a closer examination on how changes in the meridional position of the westerly jet terminate the mei-yu stage via modulating the orographic downstream circulation during its northward migration.