Dynamical connection between Great Plains low‐level winds and variability of central Gulf States precipitation

Abstract

AbstractThe Great Plains low‐level jet has been related to summer precipitation over the northern Great Plains and Midwest through its moisture transport and convergence at the jet exit area. Much less studied has been its negative relationship with precipitation over the southern Great Plains and the Gulf coastal area. This work shows that the southerly low‐level winds at 30°–40°N over the southern Great Plains are significantly correlated with anticyclonic vorticity to its east over the central Gulf States (30°–35°N, 85°–95°W) from May to July. When the low‐level jet is strong in June and July, anomalous anticyclonic vorticity over the central Gulf States leads to divergence and consequent subsidence suppressing precipitation over that region. In contrast, an enhanced southerly flow at the entrance region of the jet over the Gulf of Mexico, largely uncorrelated with the meridional wind over the southern Great Plains, is correlated with increased precipitation over the central Gulf States. Precipitation is large over the central Gulf States when the meridional wind over the southern Great Plains is weakest and over the Gulf of Mexico is strongest. This increase is consistent with the increased moisture transport and dynamic balance between loss of vorticity by advection and friction and gain by convergence.