Just before tornado formation (as in just before CC hole develops) on leading discrete supercell, Az Shear product quickly ramps up in values and would be useful in getting warning forecaster attention that there is a strengthening low-level circulation there.

Stepping back and looking at the squall line, the Az Shear product quickly allows the warning forecaster to visualize the s curvature in the squall line, and quickly isolate the central segment of the squall line that is becoming more favorably oriented with the environmental shear. Here I was able to more quickly focus attention on the segment of the line that would go on to produce a tornado.

A couple of scans later, the AzShear quickly trended up before true gate-to-gate couples appeared in the velocity product. This would help the warning forecaster get a jump on the areas of tornado formation.

Viewing angle and distance from the radar definitely important. In the images below MXX is much closer to a QLCS tornado and viewing from behind the line. While EOX is south of the line looking down the length of the line, and viewing from a greater distance. Here the low-level QLCS circulation is much more evident in MXX, while it gets lost on EOX. The area of interest is marked by the white circle on each image.

Felt the main benefit of this product may be for QLCS tornadoes, and could extend warning lead time. In the example below, a mesovortex along the line is more easily identified by viewing the AzShear product over the raw velocity data. This will allow the warning forecaster to more quickly identify the important areas along the line that will need monitoring. By expanding the color table at the top end of the color curve, it was easier to monitor the trends in the strength of the circulation. This combination could allow the warning forecaster to more quickly identify a circulation and start drawing up a warning while monitoring the trend of that circulation as input to the warning decision. Overall feel this could really help forecasters extend warning lead times on QLCS tornadoes by a couple of volume scans. This is a huge help as these tornadoes are already the hardest to warn on with lead time.

— warmbias —

In one case of a tornado embedded within the QLCS, the AzShear signatures  from both radars were nearly 100 km away. In both instances, the signature was displaced northward from the tornado path. From KEOX, the tornado path was 107.8km from the radar and was looking at approximately 1.8km up in the storm. From KMXX, the storm was 89.9km from the radar and looking at 1.4km in the storm.  Something to consider for training is the distance from the radar and any tilt from the storm.

Also interesting, is that KMXX, looking slightly closer and lower, shows a stronger AzShear signature than KEOX (0.016 s^-1 vs 0.006 s^-1). So, still a best practice is looking at multiple radars if looking at single radar AzShear, or look at the MergedAzShear 0-2km products. However, it has been noted that the mergedShear products may be more useful for QLCS type storms, vs. supercell storms.
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A little while later…

A long-tracked supercell ahead of the line exhibited very high AzShear values early in its lifetime (as high as 0.03 s^-1), but as the storm moved away from the radar, the AzShear values tended to decrease. At first, it was thought this was merely coinciding with the distance from the radar (160km at time of first image below) and how high in the storm the radar is looking (3km), however, there may also be some information about the strength of the tornado at that distance. At 160km, the AzShear strength dropped to around 0.006 s^-1. However, a short time later, there was another strong AzShear signature (>0.01s^-1) just south of there, that was also associated with a tornado path. This signature was also at 160km from the radar. Curious if it could be surmised that the northern long-track tornado was not at strong as the southern shorter track? Also of note, the southern signature was again north of the assessed tornado track.

-Tempest Sooner

While MRMS Az Shear product is useful for situational awareness of stronger storms, the jumpy nature of the updates degrades its usefulness in storm interrogation. Would really like to see single radar Az Shear in real time, as it would greatly compliment the base radar data interrogation.

— warmbias —

Attached below is one example where the AzShear from a single radar/single tilt (KEOX 0.5deg) is indicating a comparable magnitude couplet with one storm as it is for the known tornadic supercell just north of it. The important item to note here is that both of these couplets are fairly far from the radar at this point, which means the AzShear is being impacted by elevation. This would be a good case in which having a different color scale may be of use to determine the differences in strength of the couplets. This is also a case to make sure to utilize the closer radar and not rely solely on one radar that may be primarily farther (if possible). In addition, this similar intensity in couplets is significant in recognizing that a tornado may not be observed even though the couplet is identified from one specific radar in case there is not a closer radar at the time.

Below is the same circulation at  the same time, but now identified by a closer radar (KMXX 0.5deg). The difference in magnitude of the same couplets are quite apparent.

Another area to note between KEOX and KMXX is the QLCS feature, where the closer radar is able to detect better resolution of the low-level AzShear features of the line compared to the farther radar. The farther radar is clearly sampling a higher elevation/swath of time creating a broader region of maximum AzShear. Both the merged 0-2km product and the single radar AzShear product can be helpful in seeing the vertical structure  of the AzShear for this line. What’s also important at this time is the tornadic track (pink) begins around this time of the circulation.

The QLCS feature in the single-radar AzShear has a better focus and greater “resolution” of small-scale features, versus the merged 0-2km AzShear product. See image below and the mouse location of the center. The maximum center is also farther ahead of the maximums in the merged product, which is important to realize when issuing a tornado warning.  Also of note, the supercell to the northeast that is producing a tornado track is indicating multiple AzShear couplet maximum locations for the merged product (above right) vs the regular AzShear product (lower right).

I, personally, find the single-radar AzShear product closest to the radar the most useful for identifying a potential for low level tornadic circulations. I would use the 0-2km merged radar product as perhaps a “big picture, earlier lead time” type of product during the initiation stage of features.  -shearluck

Using AzShear it seems that possible areas of rotation are visible prior to rotation being evident on a velocity product or a hook is evident using reflectivity. Utilizing AzShear in a storm that is forecast to possibly become tornadic may help to identify the area of rotation sooner thus enabling the forecaster to warn sooner. – Desmond

The first feature I noticed at first glance of all of the AzShear products was the “time lag” so-to-speak of the merged AzShear products. More specifically, I compared the velocity couplet with the AzShear product and the merged 0-2km AzShear product. The merged product shows a disconnected and smeared/cluttered version of the max shear couplet region, making it difficult to find exactly which high value center you would like to focus on.

Above is an example of those three products with my mouse over the circulation center for reference. In particular, I grabbed the 0.9deg radar tilt to get the middle of the averaged layer (~1km AGL).   Because of this multi-maximum issue in the merged product, I find the main AzShear product more useful and trustworthy than the merged product with this particular case.

In addition, I was able to pick up a “debris ball” signature at a similar time. I noticed the low CC was spatially ahead of both of the AzShear product maximum couplets. This tells me to not solely rely on a one product as the main location of greatest shear or tornadic location, just because there will be a slight spatial lag between products (more noticeable in the merged product) . This also makes it clear in making sure to continue to utilize velocity data (as is well known with debris ball signatures).  Image below:

This debris ball signature was notable at both the 0.5deg tilt and the 0.9deg tilt, so I kept the 0.9deg screen for consistency.

Lastly, I noticed the strength of the AzShear couplets began ramping up and showing maximum values in prior temporal radar scans to the debris ball signature, which is to be expected. I would be more concerned if it was the other way around. Having all of these signatures in place further verifies the strength of the system.

Just before tornado development, AZ shear showed increasing values and non-linearity of positive AzShear values along the line, indicative of a tightening/developing circulation that was not  as subjectively/visually evident on Velocity/SRM. Feel this could have helped increase warning lead time due to better warning forecaster situational awareness.

Once the tornado developed, the Az Shear product made the life cycle of the tornado more visually evident. In the image below, late in the tornado life cycle, it became  clear that tornado circulation was becoming cut off from the storm inflow, behind a line of advancing outflow. If a warning forecaster were considering reissuing a TOR, this could help provide information that the current tornado may be ending soon. In the second image below, spectrum width could be used to try and visualize this process as well, but note that AzShear is much less noisy.

Comparison to MRMS AzShear: Overall found the MRMS AzShear products were useful for  situational awareness. However, artifacts in the data, like double maxes (seen below, upper left panel) due to old radar data lingering too long, limits the usefulness for in depth interrogation. It also washes out the details in storm/tornado evolution noted above. Would much rather have single radar site AzShear for warning decisions. How soon can we get this operational??

— warmbias —

One of the great things about AzShear that is not available with rotation tracks – negative values. There is a strong couplet of bright red (positive shear) just to the right of bright blue (negative shear) towards the bottom left.  What does this mean? My hypothesis is that we’re seeing anticylonic flow with a maturing RFD on the rear flank of the mesocyclone. You’ll see these shear couplets become quite apparent  coincident with supercell tornadogenesis! Several examples of this in previous blog posts. If you look closely there is a verified tornado track to the east just east of the state line. Be interesting to see how this evolves!

Next, look at the kink in the AzShear line farther north. This appears to be a developing mesovortex along that kink.  The orientation of the kink was normal to the 0-3km shear vector, which was very strong. The AzShear here is much noisier here overall due to the messier storm mode and the much smaller velocity bin sizes close to the radar.

#MarfaFront