Category: SPG2025

Comparison of GREMLIN, OCTANE, and Radar Products For Two Storms near KMAF

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

Something interesting was noted when looking at two nearby storms on 05/06 between 2146Z through about 2205Z. When looking at two thunderstorms which quickly fired up near the MAF radar, OCTANE STD data suggested the storm to the left had stronger divergence aloft. The OCTANE Speed Sandwich also showed these storms were relatively similar in strength with the right storm having slightly stronger shear, but decided to look at GREMLIN and dual-pol radar data for further analysis. It is worth noting that OCTANE data stopped coming in around 2146Z due to a power outage at CIRA. GREMLIN data clearly showed the left storm was weaker depicting much lower reflectivity. This overall aligned with MRMS data, but the GREMLIN data did smooth out higher Z values as expected. 88D radar data was then used to help investigate the two storms after seeing both OCTANE STD and GREMLIN data differ on which storm was more intense. When looking at radar data it became clear that the storm on the right was more intense with a BWER, higher cloud tops, more intense reflectivity core aloft, and stronger STD (wasn’t able to sample true STD because the storm was too close to the radar).

It was very odd to see the left storm had stronger divergence aloft in the OCTANE STD procedure yet all other data suggested the storm on the right was much more organized. There are no loops in this blog, but the weaker left storm was a left mover while the stronger thunderstorm was more of a right mover. Could this have played a role in the OCTANE STD data suggesting the left storm was more organized?

A severe thunderstorm warning was issued on the right storm before these comparisons were made as it was evident a supercell was developing. OCTANE/GREMLIN aided in quickly seeing where CI was occurring and which storms were intensifying quickly. However, using the satellite products alone to issue warnings would have been difficult. This could be due to not being familiar with what thresholds forecasters need to be looking for in OCTANE or GREMLIN in order to issue a warning. If I were in a forecast office with radar holes or beam blockage, these new satellite products would still be very helpful to interrogate storms. OCTANE/GREMLIN provided better confidence on what storms to focus on and paired well with 88D radar data for warning operations. It would be fascinating to see how this works in a location where there is beam blockage or radar holes.  

When looking at this 4 panel OCTANE STD suggests the cell on the left has stronger divergence aloft. The speed sandwich (top left) suggests the storms are relatively similar in intensity though slightly stronger shear was evident for the right storm.

The two storms on the right are the ones of interest. Ignore the far left storm. GREMLIN data clearly shows that of the storms in question, the one on the right is more intense as reflectivity values are much higher. OCTANE data went out at 2146Z so timing between products is off slightly. GREMLIN data compare to MRMS data as both showed the storm on left being less organized. MRMS was a lot easier to read though due to less smoothing.

88D Radar data clearly shows the storm on the right is more organized with a BWER, higher cloud tops, much stronger reflectivity core aloft, and stronger STD (true STD could not be sampled as the storm was very close to the radar).

– Ricky Bobby

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First Use of GREMLIN in Warning Scenario

Posted in GREMLIN, SPG2025 on by Kevin Thiel.

My first time experimenting with GREMLIN, I was able to utilize it briefly during a warning scenario.  Using the 4-panel (Figure 1) below in conjunction with radar data (KFDX), I issued a Severe Thunderstorm Warning for 60 mph winds (Figure 2).  Other than the fact this storm previously had warnings, the velocity/SRM signature was decent (certainly no slam dunk) for straight-line winds, but the uptick in GREMLIN Meso-1 combined with the increase in cloud top cooling south of Fort Sumner. Figure 3 shows a 3 minute difference showing the rapid uptick in the GREMLIN radar emulation. The CONUS radar emulation did show it, but in a warning scenario was a bit too delayed to use with any confidence to issue a warning based on its data.  It certainly helped solidify the decision after issuing the warning.

Figure 1: East Meso Sector GREMLIN and Channel 13 (left side), MRMS composite reflectivity and East CONUS GREMLIN (right side).

Figure 2: Severe Thunderstorm Warning in southeast portion of ABQ CWA.

Figure 3: The radar emulation from East Meso-sector 1 (top left) shows a nice uptick within 3 minutes with the storm south of Fort Sumner and from the previous loop from Figure 1, it continues for several more minutes. Thus, added confidence to issue a warning by 21:21z.

– Podium

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Subtle LightningCast Differences

Posted in LightningCast, SPG2025 on by Kevin Thiel.

After the first day of using the new LightningCast, I was able to notice some subtle differences between the old version (LC1) and new version (LC2).  However, I don’t have enough information to say it will impact my operations one way or the other with the new version.  It does seem the new version is a bit more detailed and possibly slightly faster with convective initiation. For instance in Figure 1,  there was an isolated storm in west-central NM where the new LC has the 75% outlining the storm by the end of the loop and the older version does not. Also, the cluster across the northern portions of NM (or ABQ CWA), the older version seems to be too quick to end the lightning as it just has a small 75% line near the border of Colorado. The new version keeps that higher probability going much further south.  In this case, LC2 might provide slightly more lead time in IDSS as well as a bit more detail in the cessation of convection.

For the last figure, I wanted to provide a snapshot of the convection and compare the two LC versions. Northern NM again was a noticeable difference between the probabilities. For the farthest northern cell, LC2 has a much larger 75% prob area while the 25/50 probs are fairly similar to LC1. LC2 suggests there might be lightning between the two areas of storms in northern NM as it has the 10% prob contour completely connected while the LC1 does not.  

LC1 suggests there might be a storm developing further east with a small 25% area near the CO border, while LC2 does not have anything and verifying with radar, appears there were only a few showers in that location. It is interesting to note the two 50% areas on the two separate storms in the southeast suggested by LC1 while LC2 keeps the contours together. And judging by the FED data, LC1 is probably more correct in this snapshot.   There are a couple other differences within that snapshot, but not entirely sure these differences would make much of an impact on a warning/IDSS scenario.

Figure 1: LightningCast and Flash Extent Density at the beginning of convection on May 5, 2025.

Figure 2: Captured a few hours in the southeast section of ABQ county warning area. A few subtle differences, but nothing notable that would change operational thinking.

Figure 3: At 20:26z, the most notable difference between the two versions is with the storm across northern NM and a minor difference with the storms in the southeast portion of ABQ county warning area.

– Podium

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