A study on local-scale thermal and dynamical mechanisms in the initiation of a squall line under weak forcing

Prediction of the convective initiation (CI) of the system was challenging due to the lack of precursors detectable by conventional observation networks. In this study, we investigated the CI mechanism using high-resolution analyses obtained from the Variational Doppler Radar Analysis System via the assimilation of radar and dense surface observations.

It was found that the CI was resulted from the interactions of a local cold air mass and the outflows from a weakened storm propagating from the nearby mountains. The cold air mass built up an unstable condition and veered air flow to form a local convergence zone in which moisture was accumulated. New convection was triggered as a result of strengthened convergence when the outflows from the dissipating storm approached the existing convergence zone.