THE SYNOPTIC-SCALE ENVIRONMENT ASSOCIATED WITH THE LOW-LEVEL JET OF THE GREAT-PLAINS

The synoptic-scale conditions of the upper- and lower-tropospheric circulation and water vapor transport during the occurrence of the low-level jet (LLJ) over the Great Plains were analyzed in terms of composite stream- and potential functions for 64 cases over a period of 11 springs (1979-89). The LLJ formation takes place when a developing baroclinic wave with an upper-level jet appears east of the Rocky Mountains. The divergent circulation associated with this baroclinic wave exhibits the coupling of the upper-tropospheric divergence with the lower-level convergence ahead of this wave as predicted by the classic baroclinic wave theory. The precipitation generated by severe storms over the surface low northeast of the LLJ is maintained by the water vapor converged by the lower-tropospheric convergence.