AzShear Effectively Detects Anticyclonic Rotation

Two supercells southwest of Lubbock produced perplexing base radar signatures with a clear right-mover reflectivity signature but anticyclonic rotation evident in storm-relative velocity. To its credit, the MRMS AzShear product picked up on the anticyclonic circulation effectively and should be able to detect the rare anticyclonic tornado!

None of the mesocyclone detection algorithms picked up on the anticyclonic rotation. Perhaps this is part of their design. The New MDA tried to detect a mesocyclone southeast of the main anticyclonic circulation on the gradient of the strong outbound velocities, but it is incorrect.

-Atlanta Braves

Single-Radar AzShear Tornadogenesis Success

Single-radar AzShear does a really good job of identifying preferred locations of circulation along a QLCS. The bullseye started as an elongated area of enhanced AzShear and then converges into a more concentrated area. This product provides a helpful heuristic for identifying tightening circulations in the midst of noisy velocity data with less-clear signatures.

One can easily see the congealing AzShear bullseye before the circulation tightens the tornado starts.

On the contrary, the Merged AzShear product demonstrated some latency issues that would lead to less confidence in circulation tightening.

This image, taken at the same time as the KEOX AzShear product, shows several unorganized areas of enhanced rotation right before the tornado started in the merged AzShear product. The tightening circulation is an important precursor to tornadogenesis and the merged product seems to struggle. -Atlanta Braves

Single-Radar AzShear demonstrates superior performance on variety of thunderstorm modes

The single-radar AzShear product shows demonstrable improvement over MRMS Merged AzShear. The spatial detail of the best circulations is much better than that of MergedAzShear, which introduces spatial discontinuity and broader areas of interest. The AzShear color table, in particular, is exceptional in highlighting developing areas of rotation along with locations of convergence along bowing segments. In the example below, you can see the rotation signatures from several discrete supercells, an embedded supercell along the line, and a couple areas of convergence associated with the QLCS. For each of these cases, the AzShear performs well and gives a representative view of the severity associated with each circulation. -Atlanta Braves

Single-Radar AzShear Product Showing Clearer Signal Compared with Merged Product

The single-radar 0.5 degree AzShear (left pane) shows a coherent area of high values associated with the velocity couplet (bottom right pane). Compare this with the merged product (upper right pane). The merged product shows a few different maxima in AzShear which is probably associated with the multiple radars and beam heights that are used to make the product. The single radar product also tracks the velocity couplet better in real time and is not subject to the lag in the merged product due to the multi-radar processing.

Ron Dayne

Mesocyclone Detection Algorithms Performance on Marginal Supercell(s)

A cluster to 2 merged supercells traversed across northern Oklahoma this evening. The loop below shows the performance of all three mesocyclone detection algorithms.

The legacy MDA performed the most poorly of all 3 detecting several inaccurate mesocyclones with inconsistent tracking. The DMD performed remarkably well in both tracking and intensity on the main meso  The NMDA experienced occasional dropouts where data was unavailable, but also performed pretty well on this storm. It particularly detected intensity well through the lifecycle of the meso.  The AzShear product also tracked the main mesocyclone very well. The DMDA performed best of all three for this storm  but the NMDA also showed promise. -Atlanta Braves

TDS CPTI Evaluation

A tornado produced a TDS in the SW part of the Tulsa WFO CWA at 21:44Z. Maximum TDS height was ~6kft.

The CPTI adequately represented an increase chance of a strong tornado (18-20%, top left).

It appears this CPTI did not have the same issues with effective STP like yesterday’s St. Louis tornado did. I like this product a lot! -Atlanta Braves

AzShear and CPTI helping to lead to tornado warning decision

On May 22 at around 2130Z, a tornado warning (test) was issued for Okfuskee County in the Tulsa CWA. Besides the usual examination of base velocity data, other tools that were used to help the decision were the merged AzShear products and the CPTI products. Watch the loop below.

In this four-panel, the upper left has the 0-2 km merged AzShear, the upper right has the 3-6 km AzShear, the lower left has the Weak/Strong/Violent CPTI products overlayed on each other, and the lower right has the 0.5 degree base velocity.

At the beginning of the loop, the max 0-2 km AzShear values were .008 s^-1, but increased throughout the loop, eventually reaching  .012 s^-1, exceeding the .010 threshold. The 3-6 km AzShear showed a similar trend.

The CPTI product showed a noticeable trend as well. At the beginning of the loop the weak/strong/violent values were 89/11/0 %, respectively. Since most every value of AzShear starts with 100% weak, the values were not overly supportive. However, by the end of the loop, the values were 75/23/2 % respectively, a significant increase in the threat of both strong and violent tornadoes. With the limited experience I have using the product, once the strong gets to 20% or higher, and the violent gets to 2% or higher, it greatly increases the confidence in needing a tornado warning.


Single Radar AzShear compared to Merged AzShear

The Fort Rucker, AL (KEOX) radar, well south of the storm of interest, shows strong azimuthal shear values up to 0.028 S-1.  The maximum values are slightly offset to the north of the surveyed tornado track (pink line) likely due to distance from the radar.  A mature hook echo is apparent in the reflectivity with a corresponding tight couplet in the 0.5 degree SRM.

The Maxwell, AL (KMXX) radar, located closer and to the west the tornadic supercell, was also detecting strong azimuthal shear up to 0.021 S-1.  An area of negative shear was located immediately to the south of the SRM couplet, along a weaker anticyclonic inbound-outbound interface.  This corridor of blue shades to bright white was a bit distracting from the more important red to white positive shear associated with the cyclonic rotation. The maximum positive shear values were located exactly on the track of the surveyed tornado.  Reflectivity and SRM KMXX data were similar to KEOX.

Merged 0-2 km azimuthal shear provided an accurate location of the meso/tornado and washed out the negative shear signal from the KMXX data. The shear values are lower than the single radar data.  Merged 3-6 km azimuthal shear is displaced to the north of the tornado path (pink line).

The merged 0-2 km rotation track has a very nice color scale (yellow to red to cyan) — key features really stand out.

CC plume or TDS were present on both radars. – Roy



AzShear picks up circulation along QLCS

The AzShear product did a nice job of highlighting and pinpointing a developing circulation along the convective line, as shown in the 2 images below from and 2144z and 2146z from kmxx. Zooming out, it’s a great indicator of where to focus on the line for a potential spin-up (bottom image from 2150z)