The use and misuse of conditional symmetric instability

A commonly employed explanation for single- and multiple-banded clouds and precipitation in the extratropics is slantwise convection due to the releas e of moist symmetric instability (MSI), of which one type is conditional sy mmetric instability (CSI). This article presents a review of CSI with the i ntent of synthesizing the results from previous observational, theoretical, and modeling studies. This review contends that CSI as a diagnostic tool t o assess slantwise convection has been, and continues to be, misused and ov erused. Drawing parallels to an ingredients-based methodology for forecasti ng deep, moist convection that requires the simultaneous presence of instab ility, moisture, and lift, some of the misapplications of CSI can be clarif ied. Many of these pitfalls have been noted by earlier' authors, but are, n evertheless, often understated, misinterpreted, or neglected by later resea rchers and forecasters. Topics include the evaluation of the potential for slantwise convection, the relationship between frontogenesis and MSI, the c oexistence of moist gravitational instability and MSI, the nature of bandin g associated with slantwise convection, and the diagnosis of slantwise conv ection using mesoscale numerical models. The review concludes with suggeste d directions for future observational, theoretical, and diagnostic investig ation.