GOES-E Mesoscale and GOES-E CONUS GREMLIN output displayed large differences for a storm in western NC.
GOES-East Meso (left) and GOES-East CONUS (right) GREMLIN output at 1951 UTC 08 May 2025.
A GREMLIN developer attributed this difference to most likely be related to the integration of lightning (1-minute for the mesosector, 5-minute for CONUS).
An odd or false reading from LightningCast occurred on the Dashboard readout on May 8, 2025. The IDSS event was the Southern Skies Music Festival in Knoxville, TN. The screenshot below shows the Max Lightning Potential (10-mile radius) increasing dramatically after 14:40 UTC while the other LightningCast options don’t suggest any potential for lightning (in next 60 minutes) until after 15:45 UTC and even then, the others didn't have any probability over 30%. On the plainview map comparing LightningCast 1 vs LightningCast 2 (Figures 1, 2, 3), the contours finally overlap the 10-mile event ring by 20:31 UTC and match up with the Dashboard probability at the same time (See Figure 2). Discussions within the HWT noted the issue could likely be a domain or pixel issue for the Max P.
Screenshot of the LightningCast Dashboard for Southern Skies Music Festival on May 8, 2025 from 19:40 UTC to 21:25 UTC. Interesting to note the blue arrows pointing to high probability of lightning depicted by the Max while the others remained less than 10% until 15:45 UTC.
Figure 1: At 19:46 UTC, the lightning potential approaches the 10-mile radius when the Max probability suggests nearly a 50% probability of lightning in the next 60 minutes.
Figure 2: At 20:31 UTC, the 10 and 25 probability of lightning enter the 10-mile radius.
Figure 3: At 21:26 UTC is when the probability of lightning really tapers off, even the Max P version.
Loop of the LightningCast version 1 and 2 surrounding the Southern Skies Music Festival.
- Podium
Though the radar-denial assignment was in GSP for the forecasters, I decided to take a look over at MRX while still avoiding radar. When looking at the OCTANE, there was a large (~50 kt) gradient in the OCTANE Speed Sandwich product, as well as a modest cooling signature and more significant divergence values up to 5*10^-3/s at 2024 UTC 08 May 2025. I’m aware that the smoothing technique can reduce the max divergence values observed, and believe the ‘high’ amount of smoothing may reduce the maximum value to the point that the forecaster will think the storm is not as intense.
OCTANE 4-panel at 2024 UTC 08 May 2025, with the Speed Sandwich (top left) and Cloud-Top Cooling and Divergence with varying smoothing techniques (none - top right, medium - bottom left, and high - bottom right). Please note while sampling the divergence value, it drops from ~5*10^-3/s for no smoothing to ~3*10^-3/s for high smoothing.
Based on OCTANE, I was leaning towards the storm being severe, so I also took a look at the GLM Flash Extent Density (FED) and GREMLIN products. There was a large lightning jump in the FED between 2006 and 2021 UTC 08 May 2025. In addition, the GOES-E Mesosector GREMLIN output showed intensifying reflectivities starting at 2007 UTC 08 May 2025.
LightningCast (V1-left, V2-right) overlaid on GLM FED and GOES-East Day Cloud Phase Distinction RGB imagery at 2006 UTC 08 May 2025.
LightningCast (V1-left, V2-right) overlaid on GLM FED and GOES-East Day Cloud Phase Distinction RGB imagery at 2021 UTC 08 May 2025.
GOES-East Mesosector GREMLIN output at 2007 UTC 08 May 2025 (left) and CONUS GREMLIN output at 2006 UTC 08 May 2025 (right).
I would go ahead and issue a Severe Tstorm Warning. Well enough, at 2024 UTC 08 May 2025, MRX issued the warning for “Ping pong ball size hail and 60 mph wind gusts”.
MesoAnywhere was very useful during this event. While there was a meso sector across the Tennessee valley, MesoAnywhere did a great job providing useful details pertaining to warning operations. Growing cu was evident early in the event along with mesoscale boundaries. The product continued to provide value during the event as other channels were used to measure storm intensity trends.
GREMLIN struggled early in the event with a storm just north of the CWA over Whitley County, Kentucky. This storm quickly became severe warned as there was a large Three Body Scatter Spike (TBSS) and impressive tall intense reflectivity core with ZDR/CC/KDP drop out. GREMLIN caught on I believe after 5min or so, but reflectivity values were still lower and not as concerning as MRMS. It was also interesting to note the storm entering western portions of the forecast area looked more intense on GREMLIN at times. If there was no radar data, GREMLIN may have made me focus more on issuing a warning for the storm to the west of the CWA. However, OCTANE data clearly showed a stronger STD signal on the storm to the north which is what made me initially go look at the 88D radar data for it.
GREMLIN was a useful tool during the event as it did catch on to stronger cells that developed, but it was slightly slower than MRMS or 88D radar data at times and would smooth out more impressive signals in reflectivity that helped issue timely severe warnings for hail. If there is no radar data, GREMLIN is certainly still a useful tool. The more tools, the better!
Here is where OCTANE data clearly showed a stronger STD signal on the severe storm to the north compared to the one entering our CWA from the west. This gave me a heads up to go look at the 88D radar data to see if a warning was warranted. The smoother STD procedures make it slightly easier to see the signal.
OCTANE STD has been one of my favorite tools in the experiment. I found it very useful to quickly identify the strongest storms in my CWA that warranted my attention. It was also helpful for understanding storm intensity trends as it has cloud top cooling overlaid in the product. The low-med smoothing and high smoothing were easier to read than the sn smoothing STD procedure. The no smoothing was splotchy which made it more difficult for my eyes to quickly discern which storms required the most attention for potential convective warnings. The tool was amazing for all of the convective events through the week, but I could see this procedure not being as useful in certain convective modes where STD signals may be weaker. I would love to learn more about what thresholds to look for in the product! I’m sure that will be a great future research project, and I appreciate all of the hard work from the researchers involved with this experiment.
- Ricky Bobby
From 1940Z to 1950Z, there was a cell developing right over Madison county. If you look at the cloud top temperatures in the Octane 4 panel below, you will see that there is cooling spike. Gremlin also picked up on high reflectivities in the same area with actual ENI total lightning increasing in density. Gremlin also showed an increased lightning intensity signal. We issued a warning on that storm and ¾ inch hail was reported.
2149Z
Interesting feature with Gremlin that would possibly suggest that there is a hook on the storm noted below to the right. Hence we issued a SVR with TOR possible tag. Looking forward to seeing if there are any reports with this storm.
-Jolly Rogers
May 8, 2025 was an interesting day for the experiment because “WFO GSP” was not allowed to utilize radar to issue severe thunderstorm warnings. I relied heavily on OCTANE Speed and CTD/cooling products and GREMLIN for making these decisions. At first, I struggled a bit with mentally shifting everything to the southeast due to parallax. After I began to utilize the ENTLN data as a proxy for storm core, it was better to estimate storm location and movement (although still not perfect). By the end of the day, I ended up issuing seven severe thunderstorm warnings. I found myself relying more on the CTD and cloud top cooling panel than the speed sandwich. Since it was my second day using the OCTANE products, I was quicker at picking up on signals in the CTD panel that suggest the presence of stronger thunderstorms. Having the CTD in one number compared to having to mentally calculate it while using the speed sandwich was helpful when working in simulated operations when a couple seconds does make a difference. I also found GREMLIN useful as a situational awareness tool to help distinguish which cells should potentially be interrogated more.
Here is a loop of OCTANE Speed Sandwich and the CTD and CTC products from two severe thunderstorm warnings I issued. The severe thunderstorm warnings were issued for the same storm, with the second one being issued as the first one was expiring. Looking at the OCTANE data combined with ENTLN (Image 1), it was clear that the storm was taking a turn to the right. I don’t know the specific values that CTD was showing, but I do believe this storm had values of 4+.
Image 1: Two severe thunderstorm warnings in OCTANE SS and CTD/CTC with Lightning Cast v1 and v2 overlaid. ~21:20Z to 21:56Z
GREMLIN (Image 2) also subtly shows this change in direction. What is interesting is that GREMLIN using ECONUS actually maxed out with a value of 60.4 dBZ.
Image 2: GREMLIN loop for the same two severe thunderstorm warnings in Image 1.
Image 3: Severe thunderstorm warning with OCTANE SS and CTD/CTC. ~21:56Z-22:22Z.
Image 4: Severe thunderstorm warning for the same time but with GREMLIN.
Another severe thunderstorm warning I issued, was showing CTD values of 4+ that prompted a warning. In GREMLIN, the strength of this cell was not as obvious in the ECONUS version, but slightly more prominent in EMESO-2. GREMLIN shows these cells basically merging, but I don’t know if that was reality. Looking at these loops compared to the movement of the lightning data, I don’t think my strom track was very good. In cases where radar is unavailable, I could see other novice warning forecasters also struggling with identifying storm track and motion when using strictly satellite data and also trying to mentally correct for parallax. This may not be an issue for more experienced warning operators though.
- Golden Retriever Lover
I experimented with GREMLIN for convective initiation on May 7, 2025. One feature that stood out and was briefly discussed amongst the developers and participants was an orphan anvil. The first animation below is the GREMLIN CONUS (bottom right), MRMS Composite Reflectivity (top right), and GOES-19 Channel 7 (bottom left) and the second animation is Day Cloud Convection overlaid with LightningCast. As you follow the anvil passing south of the Home (or the Hot Pepper Festival), GREMLIN continues to project it as a storm or at least a shower further east. LightningCast did well and held steady and kept the lightning potential with a set of updrafts to the west. Unfortunately, a meso-sector was not available at this time and thus could not compare the 1-minute data to the 5-minute data. On a side note, the MesoAnwhere did fairly well depicting the orphan anvil progressing eastward.
Images above show the orphan anvil being projected eastward and suggested by GREMLIN as a storm/shower but MRMS has no reflectivity. The lack of lightning probably hurt GREMLIN in this scenario and it was suggested by a developer that anvil temperatures can resemble cloud tops and most likely confused GREMLIN in this scenario.
MesoAnywhere showing the orphan anvil.
- Podium
