Supercells were expected to initiate along a dryline in west-central Oklahoma during Saturday evening on April 23rd. The Storm Prediction Center had issued a slight risk of severe storms in their 1630 Z (1:30 PM CDT) outlook, with the risk tornadoes (5%), damaging hail (15%), and damaging wind (15%). Thunderstorms initiated around 2200 Z (5:00 PM CDT) as shown from the Day Cloud Phase Distinction RGB animation below. As the sun began to set near the end of the animation, decreasing contributions from the green (Channel 2, visible) and blue (Channel 5, near-IR) bands created a shift to more red colors in the imagery (Channel 13, clean-IR).
An SPC Mesoscale Discussion and Tornado Watch, along with NWS Norman Public Information Graphics show the transition from the initial SPC Convective Outlook to the warnings that would later be issued that evening. (Images below in chronological order)
As convection matured into supercells after sundown, satellite imagery became confined to the infrared bands (Channels 7-16), with Clean-IR imagery most often used. Additionally, rapidly updating (1 minute) lightning data from the GLM Flash Extent Density product can provide information about thunderstorm trends between NEXRAD full-volume scans (4-5 minute updates). At night, the GOES-16 GLM detection efficiency often exceeds 90% across the south-central United States.
Intensification of two supercells and tightening of their low level mesocyclones, southwest of Oklahoma City and southwest of Stillwater, as indicated by radar prompted the NWS Norman office to issue tornado warnings for both storms. The Tornado Warning for the Stillwater supercell was issued at 2359 Z (6:59 PM CDT), and the Tornado Warning for the Oklahoma City supercell was issued at 0003 Z (7:03 PM CDT).
The animation above is from 2330 Z to 0030 Z (5 minute intervals), and shows how both storms intensified from the perspective of the GLM FED and ABI Clean-IR products. Deep overshooting tops were observed from the ABI along with notable increases in GLM flash rates. In this scenario satellite information may have provided a ‘heads-up’ on which storms to monitor, along with additional confirmation of trends observed from NEXRAD.
One-minute data was observed from the GOES-East Mesoscale Domain for both products (below). In this scenario NWS Norman also had access to the Terminal Doppler Weather Radar at the Oklahoma City Airport (TOKC), providing 1-minute radar reflectivity and doppler velocity data within the vicinity of the airport. For the supercell near Oklahoma City, this may make a forecaster less reliant on one-minute satellite data when making warning decisions. However, for the storm southwest of Stillwater no TDWR data was available. The rapid increase in lightning flash rates identified by the GLM FED product for this storm can provide additional verification for an NWS forecaster that the updraft was intensifying, and tightening of the low level mesocyclone prior to tornadogenesis may be imminent.