Widespread severe weather brought large hail, damaging winds, and tornados to two areas of the central US on 27 April 2021: Eastern Colorado and central Texas. Given the expected weather, two GOES-East mesoscale sectors were positioned over the region, with a slight N-S overlap in the middle. A simple AWIPS procedure allows one to view the two mesoscale sectors as a single product instead of two separate (overlaying) products, allowing one to view 30-sec imagery where the sectors overlap (Fig 1). If interested, feel free to reach out!
Within the southern mesoscale sector (on the edge of the overlap), a strong and long-lived thunderstorm traveling ENE across north central Texas produced hail larger than baseball size (3″ reported), along with a tornado. GOES-East 1-min VIS-IR Sandwich imagery centered over the storm revealed a large and relatively cold overshooting top and a long-lived above-anvil cirrus plume representing an exceptionally strong/consistent updraft and severe potential (Fig 2). Further, the exposed updraft and inflow region on the south side of the storm allows one to diagnose a cyclonic rotation in the updraft (mesocyclone), along with inflow feeder clouds (another severe indicator). This storm-relative example allows the user to more easily diagnose and follow storm features.
The storms in eastern Colorado were located within the mesoscale sector overlapping area, allowing for 30-second imagery. A thunderstorm developing just east of Colorado Springs produced accumulating hail. Thirty-second vis-ir sandwich imagery revealed features rising and rotating around the exposed southern portion of the updraft (Fig 3). By including the semi-transparent IR overlay for cold BTs, we can more easily focus on the warmer (non-colored) features outside of the anvil top.
Further east and a little later, a thunderstorm produced a tornado near the intersection of 3 county warning areas (BOU, PUB, GLD). This storm was warned on by all three WFO’s simultaneously! Additionally, the warnings issued by PUB were the 2nd and 4th smallest tornado warnings issued by PUB since 2007 (SBW era). This storm was also captured by the GOES-East 30-second imagery (Fig 4). Once again, the exposed updraft and high temporal spatial resolution imagery allows one to diagnose a rotating updraft.
There were several storms that produced accumulating hail across Colorado during the afternoon. These hail swaths were captured in GOES-East imagery as well (Fig 5). The Day Cloud Phase Distinction RGB highlights the hail swaths quite well (as green, similar to snow cover) compared to visible imagery alone (hail swaths and cloud both highly reflective). Dashed green lines highlight the southeast border of hail swaths. Kudos to Jorel Torres (CIRA) for pointing these out.
GOES-East 30-sec adjusted Day Cloud Phase Distinction RGB imagery focused on the El Paso County storms highlights the cloud detail in the thunderstorms as well as the hail swaths at moments between cloud cover (Fig 6). Hail swaths can be found just east of Peyton and east of Yoder.
The hail swaths could also be diagnosed in the high resolution VIIRS imagery, in both the Day Cloud Phase Distinction RGB (green), and snowmelt RGB (dark blue; Fig 7).
A video montage shows the impressive El Paso County hail swath:
Bill Line, NESDIS and CIRA
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