Very deep convection developed over the western Mexico near the Gulf of California during the late afternoon hours of 20 August 2019, lasting into the early evening. This area of convection produced overshooting tops with IR brightness temperatures less than -90C (Fig 1)!
Analyzing a nearby sounding, these storms developed in an extremely moist environment (TPW=2.49″), very strong instability (MLCAPE = 4660 j/kg) and a very high equilibrium level (around 16.5 km). Based on the sounding, the -90C observed IR brightness temperatures likely put the OTs over 17.5 km above the surface!
Corresponding visible imagery of one of the storms is equally impressive. The final frame shows an OT penetrating deep across the equilibrium level casting an obvious shadow on the anvil (Fig 3).
Finally, a VIS/IR comparison of a -90C OT (FIg 4).
Bill Line, NWS
Satellite Liaison Blog 