What causes the most “bust” chases?
This is no contest: the cap — a layer of relatively warm and stable air above the surface which stops air parcels from rising any further and becoming thunderstorms. On some days, the cap is too weak, and a squall line quickly erupts for hundreds of miles, greatly reducing the chances of seeing a tornado from an isolated supercell. Sometimes, the cap and lift are both strong, and a few storms do form (such as the 12 May 1996 “I-70” supercell in Kansas). Other days, the cap and lift are both weak, resulting in a seemingly random pattern of chaseable storms (3 May 1999 being an extreme example!). But when the cap is too strong, nothing else matters; it’s “bustola” time. Many chasers have driven home sporting a sunburn and festering with frustration when every ingredient was in place — except enough lift to break the cap. For more details on the cap and how to analyze it, see this tutorial by Tim Marshall.
