Top left: GREMLIN simulated reflectivity
Top right: ELTLN lightning 1 min flash, 5 min CG flash, NLDN 15 min CG Flash 1km
Bottom left: GOES East Meso-1 Channel 13
Bottom right: GREMLIN radar with GLM flash extent density image overlaid
While the environment for this area was questionable (shear was <30kts) and we were unsure whether we wanted to even use this sector, it ended up being a fruitful area to observe signals and experience challenges associated with warning without radar in real-time.
Generally, the rhythm we fell into for warnings was using the GREMLIN product to track the storm cores and draw the polygon and cross-referencing with ground-based lightning networks to make sure parallax was accounted for.
Prior to making warning decisions, or when deciding to cancel an active warning, we would monitor the lightning (ground-based and GLM) to make sure it was increasing/intensifying or at least sustaining. LightningCast was consistent in probabilities for the warned area, so it did not provide much of a signal in terms of convective intensity and maintenance of severe storms.
Left: Day Cloud Phase Distinction satellite RGB with GLM and LightningCast version 1
Right: Day Cloud Phase Distinction satellite RGB with GLM and LightningCast version 2
Top left: GREMLIN simulated reflectivity
Top right: ELTLN lightning 1 min flash, 5 min CG flash, NLDN 15 min CG Flash 1km
Bottom left: GOES East Meso-1 Channel 13
Bottom right: GREMLIN radar with GLM flash extent density image overlaid
Around 19:45 UTC, lightning intensity trends (as observed on GLM) combined with cooling intensity and divergence of the cloud tops on OCTANE products led to the decision to issue a Severe Thunderstorm Warning with hazards of 60 mph winds, penny-sized hail, torrential rainfall, and lightning. Around 1951 UTC, a report came in indicating that a tornado was on the ground just north of the St. Louis metropolitan area, within the Severe Thunderstorm Warning polygon we had issued based on GREMLIN data. This prompted the issuance of a tornado warning, in combination with new SPC mesoanalysis data showing low-level hodograph curvature that would support low-level rotation using the “two out of three” framework (radar, reports, environment).
SPC Mesoanalysis 20 UTC June 4 2025: Hodographs
Top image: GREMLIN data with simulated Severe Thunderstorm Warning and Tornado Warning polygons
Bottom image: Graphic for posting to social media and Slack warning the public and partners about this high-profile hazard in a major metro area.
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