Severe storms produced large hail (including significant) and tornados across Wyoming and Colorado on 29 July 2018. Strong northwest flow over a moist airmass led to very favorable shear and instability across the region, and a SPC Enhanced Risk for severe was in place. GOES-16 1-min imagery was available to support NWS forecasters during the event. Storms early on produced overshooting tops and above anvil cirrus plumes, a signature indicative of severe and significant severe potential. The plumes appear as smooth cirrus cloud features emanating from the overshooting top and downstream over the storm anvil. Cumulus clouds are also analyzed being drawn into the southern regions of the storms, indicative of strong inflow winds.
A little later over east-central Colorado, a severe storm developed that produced a measured wind gust of 83 mph, along with hail at least 2.75″ in diameter (baseball). GOES-16 1-min imagery of this storm showed a large and persistent overshooting top and an above anvil cirrus plume (VIS, Fig 2). The corresponding 1-min IRW imagery (Fig 3) shows a large overshooting top (round region of coldest pixels) along with a relatively cooler area immediately downstream of the overshooting top (completing the thermal couplet) and a relatively cool region extending downstream above the anvil (above anvil cirrus plume). Overlaying a semi-transparent IRW on the VIS, we get the sandwich image combination (Fig 4). Radar imagery of the storm showed reflectivity over 80 dBz along with significant beam attenuation, indicating a lot of hail (Fig 5).
Bill Line, NWS