GREMLIN and The Orphan Anvil

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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LightningCast Comparison for Cabbage, Potato, and Bacon Festival near Hastings, FL (JAX CWA) on Wednesday May 7th

LC V2 did better with lightning cessation showing lightning probabilities dropping quicker as convection moved east of the DSS event which it title “HOME”. This allowed for more timely DSS updates to partners mentioning the lightning threat was diminishing, at least over the next hour or so. LC V2 also did better with storms to the south which we will talk about more below.

LC V2 showed higher probabilities for lightning quicker for developing storms near southern portions of the county warning area. V2 also lowered probabilities quicker once the storms temporarily pulsed down. I do believe one or both of these storms eventually pulsed up again after this though so it is possible V1 performed slightly better in this scenario by keeping slightly higher lightning probabilities.

LC V2 had tighter areal extent of lightning probabilities overall which was more helpful and accurate. May just need to be a little more weary of sensitivity to decreasing lightning probs too quickly for pulse thunderstorms in the summer.

– Ricky Bobby

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Tulsa Severe Weather Event

An upper low across central Oklahoma allowing for an unstable environment across the Tulsa CWA. At 19:38Z,  clearing noted across the western  half of the CWA allowing for cu development across this region. At this time, limited to only CONUS level satellite imagery as mesoscale sectors are elsewhere.

21:00, towers with anvils noted and are beginning to shear off of the updraft.

I felt that lightningcast overperformed in pinging on lightning that never transpired in real time.

-Jolly Rogers

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

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

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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Basic OCTANE Cloud Top Divergence Comparison

This is a basic comparison between three options for the OCTANE. The top animation is No Smooth, the middle is Medium Smooth, and the bottom is High Smooth.  For starters, I do like the looks with the smoothing, it is easier on the eyes and rids of any excess noise.  I feel this helps to recognize trends easier and remain focused on those trends through the animation.  In this loop, following the regenerating updrafts west of College Station and Snook, TX, was somewhat easier to follow on either the medium or high smooth.  Smoothing out the excess noise around the updraft helped remain focused on the primary portion of the storm.  The warning issued was based on radar data, but could imagine the Cloud Top Divergence being a helpful tool in warning decisions if radar data wasn’t available. It certainly is a “confidence booster” or a nudger if you’re on the fence for a warning or not. It would be interesting to correlate the CTP (to hail size, wind, and/or if a tornado was produced. Obviously this would take some extensive research.

-Podium

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Lake Charles May 6th event

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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Houston CWA May 6th event

 Started out issuing a warning for parts of northwest Houston’s area based on info from the Flash density product.

3:06 PM. Using Octane, noticing a cluster of convection that is developing and becoming more interesting for warning purposes.

3:38 PM Severe Tstorm with tornado warning out. Special feature noted on Octane Speed Product where the updraft was reisting ambient wind flow as the storm intensified noted by cyan colors on LA/TX state line near Shreveport.

-Jolly Rogers

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OCTANE Cloud Top Divergence Comparison

This is a comparison between three options for the OCTANE Cloud Top Divergence. The top animation is No Smooth, the middle is Medium Smooth, and the bottom is High Smooth.  For starters, I do like the looks of the smoothing option, it is easier on the eyes and rids of any excess noise.  I feel this helps to recognize trends easier and remain focused on those trends through the animation resulting in being particularly helpful in real-time operations since the warning meteorologist eyes are constantly moving from screen-to-screen.

In this loop, following the regenerating updrafts west of College Station and Snook, TX, was somewhat easier to follow on either the medium or high smooth.  Smoothing out the excess noise around the updraft helped remain focused on the primary portion of the storm.  The warning issued was based on radar data, but I could imagine the Cloud Top Divergence being a helpful tool in warning decisions if radar data wasn’t available. It certainly is a “confidence booster” or a nudger if you’re on the fence for a warning or not. It would be interesting to correlate the CTD (to hail size and possibly wind and/or if a tornado were produced) if given certain thresholds such as the multitude of hail research that has been conducted from radar in recent years.

Below are the three CTD options at 20:29z on May 6, 2025.   There were a pair of updrafts near College Station and were clearly evident on the cloud top divergence.  However, some subtle differences showed up between the smooth and the no smooth options.  In the yellow box, the High Smooth seemed to smooth too much compared to the No Smooth and Medium. Similarly in the black box and next to the black arrow, it seemed to be overly smooth and completely get rid of some features that might evolve into something notable later.

There are very subtle differences, especially between the two smoothed loops, and if given the choice, I’d lean slightly towards the Medium Smooth based on the High Smooth potentially smoothing out some important features and the No Smooth being too harsh on my old eyes.

– Podium

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