Synoptic type events typically occur in the spring and fall months upstream of a progressive upper level trough. Training of convection and heavy rainfall occurs to the north of a warm front and associated southerly low-level jet, within a region of maximized low-level convergence and isentropic up-glide. Training behavior results from a balance of low-level rain-cooled convective outflow and opposing inflow from the low level jet, which continuously supplies elevated conditionally unstable air to the MCS.
Warm season type events occur predominantly during the summer months in association with the right entrance region of an anticyclonically curved jet stream/streak. Training of convection again occurs north of a quasi-stationary west-east oriented boundary and associated southerly low-level jet. Gravity waves generated by latent heating from initial convective development become near-stationary upstream of the MCS, vertically agitating an elevated conditionally unstable layer supplied by the low-level jet and generating moist-absolutely-unstable (MAUL) layers. Convection erupts from MAUL layers on the upstream side of the MCS where a convectively induced horizontal perturbation pressure gradient field modifies the environmental wind field favorably for low-level convergence and continuous convective regeneration.
These results illustrate that while the two types of convective systems identified here are commonly grouped into the same MCS archetype, their associated synoptic scale environments and governing dynamics exhibit noteworthy differences, highlighting the utility of principle component analysis in refining pre-existing subjective MCS archetypes.