Tornadic Supercell and AzShear and ProbTor Ramp-Up

The storm along the Milam/Burleson county line began to wrap up showing increasing Merged 0-2km AzShear and a stronger velocity signature. From 2204z – 2208z there was a brief couplet from this storm and the FWD and HGX offices, and the HWT forecasters all tornado warned this storm. You can see the Spectrum Width maxima at the point of the couplet and along the leading edge of the bowing segment to the south of the couplet. There is also an inflow notch as well all situation near the bookend vortex. The big thing to note is how the AzShear Merged product ramped up from 2154z to 2204z. This also impacted ProbTor. The trend went from:

  • 2149z: ProbTor 11%
  • 2154z: ProbTor 60%
  • 2159z-2206z: ProbTor 84%
  • 2208z-2212z: ProbTor 86% (2207z is when WFO FWD issued their warning)

ProbTor maxed out at 87% from 2216z-2218z while the couplet became less gate-to-gate. If you used a ProbTor threshhold of 60% that would have given 15 minute additional minutes of lead time, while a threshold of 80% would have given approximately 8 more minutes of lead time. As of writing this blog (2240z) there are no LSRs reporting anything in terms of damage or tornadoes with this storm.

-Alexander T.


ProbSevere Large Areas Impacting Threat Percentages

With this storm going through Milam and Burleson Counties in South Central Texas ProbSevere is saying 90%+ for ProbWind and only like 15% ProbTor. One possible reason for the lower ProbTor may be the large area that ProbSevere is tracking as one storm. Yes, it certainly is one large bowing line segment, but if you look at the AzShear Merged data in the lower right you can see localized maxima in Milam County. While there is not a defined couplet at this point there is some bookend vortex action going on in the area of the AzShear maxima. If the ProbSevere was broken into two different areas would the ProbTor and/or ProbWind be even higher for the Milam County storm due to the locally higher AzShear? I would say probably so! Because ProbSevere is encompassing the entire line segment the values of AzShear going into ProbSevere are probably dampened some from the less active southern part of the storm.

-Alexander T.

HGX Mesoanalysis

Storms are approaching the HGX CWA. GOES-16 imagery shows amply cumulus development across much of the CWA. With temps in the upper 70s and dew points in the upper 60, I expect there to be ample instability in this environment.All Sky LAPS retrievals indicate ML CAPE just shy of 1000 J/kg, but with this environment, I would expect instability to be higher. The modified NUCAPS shows a profile more in line with what I would expect to see. In this profile, the surface dew points were close to what surface obs show, but the surface temp did need to be adjusted up a bit. This sounding, coupled with analyzed deep layer shear, leads me to think severe weather is a possibility in this area.Sandor Clegane

Waiting on convection – diagnosis and investigation of products

Corpus Christi —

In investigating the environment we’ve deemed the convection to be more or less dependent on synoptic forcing via the cold front dropping southeast.


In A, plotted is Total Precipitable Water along with SPC Convective Outlook and analyzed fronts. A couple of things can be noted: TPW is very high under the Slight Risk, and it is displayed very nicely with good resolution contained within the gradient. This is a good example without going into too much detail about how our environment is primed for severe weather. However, NUCAPS Gridded Data has not come into our area as of 20z. This makes it hard to test the product and how it captures the boundary layer. 

Now, we wait.


As we wait for the cold front to drop SE, our attention is focused on convection happening in NE Mexico (pictured in B). These cells popped up right along the CAPE boundary between values of 300 j/kg to 1500 j/kg.


As can be seen in C, the GLM has indicated these storms contain lightning, thus they are intensifying in nature. We will now be monitoring the hail threat.



ProbSevere: Color Table Modification

While I’ve been a big fan of the ProbSevere Model for some time now, the default color curve has always been a little challenging for me to differentiate between the different percentages. Trying to find the right balance between the radar color tables and ProbSevere I know can be tough, but here’s my first go at attempting to better differentiate when the percentages move into the next 10% range. Unfortunately, I’m unable to really test this modified color table out since we’re currently not getting radar data in from the Davenport area, so will reassess this once I’m able to overlay the model output with radar imagery. But, just having the colors pop a little more is already helpful to me! Oh, and I’m very appreciative that ProbSevere v.2 now includes the separated values (i.e. ProbWind, ProbHail, ProbTor). Looking forward to testing this out once there’s a case to evaluate with it.

*Note: As of this posting, WFO DVN issued a Severe Thunderstorm Warning.


ProbSevere vs. LJDA

One of our primary goals today was to examine the relationship between the ProbSevere model and the lightning jump detection algorithm. A strong storm fired on the front range of the Rockies, just west of Denver. The ProbSevere model noted strong satellite growth rates in a moderately-sheared environment, with MESH only 0.17″. The probability of severe was 33% at 1920 UTC.  At this time the PGLM indicated a flash rate on the order of 6 flashes per minute.  Two minutes later, at 19:22 UTC, the ProbSevere was 46%, as MESH increased to 0.33″, and the total flash rate at 8 flashes per minute per pixel.   Over the next 4 minutes, two consecutive lightning jumps were indicated in excess of 2 sigma as the total flash rate rose from 8 to 20 flashes/min/pixel (2 sigma jump at 1922 UTC, 4 sigma jump at 1924 UTC).  ProbSevere increased to 66% at 19:24, and 77% at 19:26 (MESH = 0.71″).  This storm intensity information highlighted the rapidly developing updraft within the storm; signalling the potential for severe weather was increasing as the first storm in the area approached the Denver Metro Area.The NWS issued a severe thunderstorm warning at 19:36 UTC. The jump in ProbSevere (46% to 66% from 19:22 to 19:24 UTC) and the 2-sigma and 4-sigma jumps from the LJA (at 19:23 and 19:24 UTC, respectively) may be able to give forecasters enhanced confidence and perhaps more lead time to initial rapid development in the storm, and potential severe hazards. Animated GIFs for Flash Extent Density (top), Lightning Jump Detection Algorithm (middle), and ProbSevere (bottom) from 1920 UTC to 1930 UTC can be seen below.


Additional lightning jumps were noted at 1943 UTC (3 sigma) followed by multiple 2 sigma jumps at 2000 UTC, 2001 UTC, and 2004 UTC, and another 3 sigma jump at 2005 UTC.  These additional jumps were additional signals that the updraft in the storm was re-intensifying and continued to have the potential to produce severe weather.  Thus any warning that was issued should remain in effect. During this time period, ProbSevere remained at or above 98%. The first tornado report associated with this storm was at 2005 UTC and hail to the size of golf balls were reported in the Denver Metro.  Also hail depth of at least 5 inches was reported at Denver International.

In this case, ProbSevere and LJDA both displayed the rapid intensification of the updraft, and could be especially useful in identifying the first severe storm of the day, and the maintenance of the ProbSevere and additional lightning jumps continued to highlight the threat of severe weather as the storm continued eastward as the storm propagated eastward.  This information is a high temporal resolution (1-2 minutes) and provides additional data points that can fill gaps between radar volume times.