Category: GREMLIN

4-Panel GREMLIN Satellite

Posted in GREMLIN, SPG2025 on by Kevin Thiel.

We discussed how we would handle warning this cluster of storms around 20:30Z Mon 19-May-2025, whether we would do one big SVR warning encompassing the whole cluster or concentrate into individual storms with different hail sizes and/or wind speeds. If I was warning this and saw a similar presentation in the radar for both clusters, I would begin with a larger SVR encompassing both storms.

The satellite product I use most often for cloud top cooling/warming for diagnosing convection growth is the Ch 13 IR. By using Ch 13 IR satellite and GLM Flash Extent Density, that helped me determine which updraft was the strongest and/or tallest. The overshooting top visible in the bottom left corner with the northern storm cluster suggests a quickly growing updraft that may start to produce large hail (and/or damaging winds) soon given the lapse rates and the explosive environment. Corroborating this with GLM FED and discussing with the group, we also came to the conclusion that the southern cluster of storms is probably broader but not as strong given its broader but less concentrated lightning presence, and might even be weakening below severe limits. With this information, I would have probably SVSed my warning to only include the rapidly growing northern cluster and maybe upping the hail size.

GREMLIN also tends to agree that they start off with relatively similar intensities, but eventually the northern storms take precedence. Using all four of these products together from the start to finish of the storms’ lifecycle would inform my warning decisions for initial issuance, SVSing, and eventual EXPing or reissuing downstream.

4 Panel loop below.

Loop of GREMLIN (top right), Composite Reflectivity (top right), Ch 13 IR (bottom left), GLM FED (bottom right)

– millibar

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GREMLIN Comparison

Posted in GREMLIN, SPG2025 on by Kevin Thiel.

While it was noted in training materials that the GREMLIN based on 1-minute mesosector imagery would be a bit ‘noisier’, I wasn’t quite prepared for just how much that could show up. This is likely due to the use of the 1-minute lightning data, which will naturally be noisier than the 5-minute data for the CONUS-based GREMLIN. As you can see in the GIF below, this shows up especially strongly in the anvil regions of mature storms, where lightning in the anvil may be less frequent, and thus more noisy in the 1-min data, but the noisy data does show up somewhat elsewhere, too.

Comparison of GREMLIN based on GOES East Meso-1 (left) and GOES CONUS (right)

This would be a case where one would want to have the image looping to make it obvious what was going on, so you could know to ignore those simulated ‘returns’.

The mesosector GREMLIN also tends to have a bit ‘sharper’ resolution in most of its features, and also tends to have higher peak simulated reflectivity, again possibly/probably owing to the 1-min lightning data, which should be a bit less broadbrushed compared to the 5-min data used for the CONUS GREMLIN.

– Marko Ramius

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OCTANE-GREMLIN Comparison for May 8th convection across eastern Tennessee

Posted in GREMLIN, OCTANE Speed Sandwich, SPG2025 on by Kevin Thiel.

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

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Severe thunderstorm warnings ONLY using satellite data

Posted in GREMLIN, LightningCast, OCTANE Speed Sandwich, SPG2025 on by Kevin Thiel.

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

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Greer Severe Weather Blog

Posted in GREMLIN, OCTANE Speed Sandwich, SPG2025 on by Kevin Thiel.

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

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GREMLIN and The Orphan Anvil

Posted in GREMLIN, LightningCast, OCTANE Speed Sandwich, SPG2025 on by Kevin Thiel.

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

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Analyzing OCTANE and GREMLIN procedures for May 7th event over JAX forecast area

Posted in GREMLIN, OCTANE Speed Sandwich, SPG2025 on by Kevin Thiel.

GREMLIN was doing relatively well early in the event capturing more intense cells firing up along the Sea Breeze boundary.

Some issues were then noted with new development along the boundary after initial cells began to collapse with convective cloud debris and leftover anvil overhang. GREMLIN hardly shows any reflectivity where MRMS shows new cells developing to the west of the more intense cell offshore.

GREMLIN struggled some with this cluster of storms further south as well, but it did do a great job of capturing the more organized cells.

The more intense cell shown in the GREMLIN figure above did intensify further with OCTANE products showing strong Storm Top divergence and shear. The speed sandwich showed nearly 40 knots of shear at this point and no smoothing STD had peak values near 5.5 10^-3 -s. The medium smoothing had values around 4-5 10^-3 -s. This was the strongest signature of the day and questions were raised on if a severe t-storm warning would be issued if there was no radar data. It is hard to answer this question given how new these Satellite products are to me. Knowing the environment was marginally supportive for downbursts or severe hail and this was the strongest signal of the day I may have issued a severe thunderstorm warning. It would have been a lower confidence warning, but it is better to be safe and issue the warning given there is no radar data theoretically.

A few scans later OCTANE products clearly showed the storm had already reached peak intensity and was beginning to weaken. Weakening storm top divergence/shear in speed sandwich along with weaker gradient in wind speeds were the signals noted. This would have given me the confidence to know another severe thunderstorm warning downstream was likely not needed. GREMLIN also showed reflectivities beginning to decrease around or shortly after this point providing greater confidence. Forgot to grab an image of GREMLIN for this.

– Ricky Bobby

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Day 3 observations

Posted in DSS, GREMLIN, LightningCast, OCTANE Speed Sandwich, SPG2025 on by Kevin Thiel.

LightningCast/MesoAnywhere for DSS Event

We were operating as NWS JAX on 5/7/25. There was not a huge severe threat, but there were cells that produced a lot of lightning. Our DSS event was the Cabbage, Potato, and Bacon Festival in Hastings, FL (labeled as “home” in AWIPS). As soon as the   day started, there were cells within the range of the festival, with our primary focus on lightning cessation. One of the first things I noticed was that for the cells to the north of the cells, LightningCast v1 had a wider spatial extent of the probabilities than v2 for areas of decaying convection. I assumed this was because of the MRMS data as there were lower MRMS -10C reflectivities in the northern edges of the convection where the lower v2 probabilities were.  I was curious how that would impact the probabilities for the event as the convection began to decay there and how it related to notifying the event of an “all clear”.

Image 1: LightningCast data v1 vs v2 from 19:50Z to 20:11Z.

With respect to the event itself, using the lightning dashboard (image 2) was helpful. Probabilities both in v1 and v2 were high for the beginning of the day in the middle of all the convection. Probabilities started to decline around 20:15Z. Initially, v1 was declining faster, but by 20:30Z, v2 was declining at a faster rate than v1. There was still lightning within the 10 mile radius during these declines, but v2 it seems that v2 caught on to the decay a bit faster. This is also shown in the LightningCast loop from AWIPS (image 3) where v1 had a larger spatial extent to the higher probabilities for longer. I used LightningCast probabilities in my DSS messaging. When the probabilities were going down, I used a number in between each version for the probability I used in the message. I also utilized MesoAnywhere 1 minute Channel 13 data once it became available for us to monitor the potential for new convection behind the main cluster of cells. There was not much being shown, which made me more comfortable noting the event of an all clear.  Probabilities eventually did start to go back up after 21:15Z because there was a lot of convection to the north and south of the event.

Image 2: LightningCast Dashboard for the Cabbage, Potato, and Bacon Festival in Hastings, FL.

Image 3: Lightning Cast comparison loop from 20:43Z to 21:32Z.

Octane and Gremlin

Today was the first day that I used Octane. After getting some training on it from Jason, my first impression of it is that it would be a valuable resource for situational awareness for developing convection and alerting you to where stronger thunderstorms are. This could alert a forecaster to a cell that they may need to interrogate a little more. During warning operations, if radar data is available, I do not think that a warning operator would have enough time to use this in their data analysis, but the warning coordinator or mesoanalysis person would probably find this tool helpful. We went through a thought exercise about how we would use this tool when radar data is unavailable. During times like that, the radar operator would probably find this tool helpful because the storm top divergence and the speed sandwich offers information that radar operators look in radar when assessing thunderstorm strength. With respect to the individual options, I found myself using the speed sandwich more initially because I was able to infer the storm top divergence in a unit that I am used to. However, the more I get comfortable with the actual CTD units and colors, having it paired with the storm top cooling would provide me more information overall than the speed sandwich during warning operations. If I only had satellite data, I would probably be pretty liberal with my warning issuance. There was a cell near Juniper Springs around 22Z, where the speed sandwich and CTD tools were showing relatively “stronger” signals (stronger is relative since there were not many strong signals today). Looking at radar data (MRMS MESH, VII, dual-pol data) and knowing the environment, I did not think the cell was producing severe weather. I am not very comfortable just yet with the thresholds in these Octane products, but given the environment was supportive of marginal severe weather, I may have issued a warning in this instance. Both the SpeedSandwich and the CTD displays were indicating the storm was weakening though, so I also might not have either. As others have noted the last couple of days, the MedSmooth CTD was the one I preferred.
Image 4: Octane Speed Sandwich and Cloud Top Divergence and Cooling from 21:54-22:21Z=
Looking at GREMLIN for the same storm, it seemed to have picked up on the stronger signals of the specific cell and would be useful for pinpointing the storm with the highest “potential” in this instance since it was the one with the higher reflectivity values. I don’t know if I would make a warning decision specifically off of this product, but if I had it available in addition to other satellite data, I may be more inclined to issue a warning or an SPS if the environment is supportive of it.
Image 4: GREMLIN 20:31Z to 22:21Z
Unrelated to the previous storm, this was another snapshot I took of GREMLIN. There was an outflow boundary (not visible in this image) that was traveling southward and sparking new convection as it interacted with the sea breeze. A small cell that was relatively strong quickly developed to the southeast of the Jacksonville Airport. While reflectivities were picking up on MRMS, satellite didn’t pick up on it as quickly. GREMLIN did not catch this initiation.
Image 5: GREMLIN at 20:01Z.
There was a cell that developed along a outflow boundary very close to the radar. Satellite data was not really picking up on it with little cooling cloud tops so GERMLIN completely missed it.
-goldenretreiverlover
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Lake Charles May 6th event

Posted in GREMLIN, LightningCast, OCTANE Speed Sandwich, SPG2025 on by Kevin Thiel.

GREMLIN was helpful early in the event to quickly identify most intense thunderstorms developing across SE Texas, but as more convection developed it became less useful. A severe thunderstorm warning was issued for the cell highlighted in blue on the top right panel of Figure 2 which shows MRMS. GREMLIN data hardly shows much lower reflectivities for the severe cell as more frequent lightning producers to the northwest are likely causing it to struggle.

88D radar data showed a tall and strong Z core. Strong STD and lower ZDR/CC values were also noted aloft though were not shown here.

This was right at the end of the day so didn’t have time to issue more warnings, but storm to the NW is likely severe by this point just given supercell characteristics.

OCTANE STD showed the severe cell with cooling cloud tops and then showing a STD signal as the storm quickly grew taller than an anvil from an upstream thunderstorm. The STD signal was rather weak though and was even weaker than some sub-severe storms which developed across East Texas. This could have been due to disrupted flow from upstream convection. The product did still help me quickly realize there was new convection developing over SW LA and led to me eventually issuing a warning after doing further analysis on 88D radar data.

Didn’t see too many significant differences between LC V1 and V2 overall. I did find this image interesting as convection developed across SW Louisiana LC V1 had higher probs over a larger area before V2. Further north across central Louisiana, there was additional convection developing under thicker cirrus where V2 did a better job showing higher probabilities of lightning. LC V1 only had low or moderate probs at most while there were a few lightning strikes already occurring. I forgot to save an image from that example.

– Ricky Bobby

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