Regional Identification Methods and Extratropical Dynamical Linkages to Surge Events in the North American Monsoon System

Transient behavior of the North American monsoon allows for episodic northward pulses of atmospheric moisture into the southwestern US. These surge events pose a difficult forecasting issue due to a lack of an accepted means to qualify their occurrence and the ill-defined influence of tropical and extratropical features that enable and drive them. Surge events have often been misidentified because of biases in ground observation site data related to localized influences not associated with surges. In this study, a novel method for the classification of surges is proposed based on their regional, rather than local, signature. This method is shown to be more accurate in detecting surge events related to widespread summertime precipitation events across the Desert Southwest of the US than previously established methods. To further the understanding of mechanisms responsible for surge initiation, this study explored the influence that midlatitude troughs have on surges. Midlatitude troughs were shown to initiate surges that result in widespread precipitation across the southwestern US. Interactions where midlatitude troughs and tropical easterly waves jointly produce surge events were observed to dramatically increase the northward momentum and moisture flux and drive precipitation further north than typically occurs with the North American monsoon system