As we move along through this case, east of the convective line exists a plethora of potentially potent supercells; each is producing high values of AzShear from multiple radars as well as in the merged products.  But what about further back west with the incoming convective line that is looking a little QLCS-ish?  Here is an example of how three products can be used together to help determine areas of increasing potential for rotation.

First, from KEOX:

A broken line of storms has an area of enhanced inbound velocities with a stronger storm in the line (just south and east of the target/bulls-eye/red and white marker).  The single-radar AzShear shows cyclonic shear all along the leading edge of the line but with an enhanced area of shear along a small bowing segment.

Now take a look at KMXX AzShear (with the velocity and reflectivity staying with KEOX):

Only 1 minute 30 seconds after the KEOX scan, this shows what will likely be an area of rotation higher up in the storm (2.5 km up from KMXX vs 1.2 km up from KEOX using the beam sampling tool) so there is something aloft as well.  O.K….thinking along the lines of mid-level rotation above a strengthening area of shear at the lowest tilt; interesting.

Finally, looking at the merged 0-2km AzShear (again with the velocity and reflectivity products remaining at KEOX):

Yup, there could be something there BUT the big caveat is that you don’t want to get caught thinking that this feature has a long “history” since that trail extends south and west from our area of interest.  Nope, that’s the shear along the leading edge of the convective line.  However, it does show that the strongest AzShear values are close to our marker/area of interest so id doe need to be watched for future potential strengthening…(post-note: nothing was reported/observed tornado track wise)

-Dusty

Let’s say your storm’s velocity data crosses into the dreaded “purple haze”. This  loss of velocity data also results in a loss of single-radar Az Shear data. So, what do you do if you’re on the warning desk? Do you scream and panic? No, that wouldn’t be ideal. Rather, take a look at the Merged-shear products. In this example, a strong storm moved into the “purple haze” of KMXX’s radar, thus losing reliable velocity and single-radar AZ Shear data. However, surrounding area radars are still getting a good reading on the storm, and thus the operational forecaster can utilize the Merged Shear products to calm their nerves as to whether the storm is still worthy of maintaining focus on it.

What happens if convection moves far enough from your radar to where the single-radar Az Shear becomes less reliable? The Merged shear products can then potentially be useful! In this example, the storms have moved to the edge of the useful range of the KMXX radar. The KMXX single-radar Az Shear (top right) values are much weaker/potentially less reliable and the KMXX velocity data (bottom right) also leads to uncertainty as to how much attention should still be given to the ongoing convection. Utilizing the Merged shear products (left) indicates that the convection is likely still strong (at a minimum) and warrants further investigation.

When initially switching Az Shear from KMXX to KEOX, I was surprised as to how strong the Az Shear values were from KEOX well before they increased from KMXX. This got me thinking as to how Az Shear could be used in a situational awareness type of setup.

Given that the storm was >100km from the KEOX radar site, the higher beam height from KEOX was likely picking up on what was going on in the mid levels of the storm (although the beam width was also much greater). A good situational awareness “best practice” could be to have a procedure or display that would display all the single radar Az Shear values  from both the home and surrounding radar sites into a multi-panel display. Noticing that a particular radar was showing higher Az Shear values could lead the operational forecaster to focus more attention on a particular storm, with the idea of the earlier increase in Az Shear potentially leading to a faster lead time down the road.

KEOX single radar AZ Shear is on the left. KMXX single radar AZ Shear is top right, and KMXX velocity data on bottom right.

Single radar AZ Shear would be very beneficial to the field offices. While the merged Az Shear is useful in assisting with various trends (per se) and overall placement of stronger values, having the single radar data provides the fastest information to the forecaster with the best resolution. During a real-time situation, having instant data rather than data that is ~2 to 3 min old can make a significant difference.

This image shows the single radar AZ Shear data on the left, with the merged 0-2km on the bottom right, and merged 3-6km on the top right. The place marker in each image shows where the “area of warning interest” is currently located.

In this example, I would  feel quasi-comfortable issuing a tornado warning before a tight couplet appears on velocity, given the increased Az Shear values that occur about a volume scan before the low level velocity tightens up. The caveat is that the forecaster must fully know the atmospheric setup before focusing purely on Az Shear data.

These images indicate, from top to bottom, the initial enhancement from Az Shear before the velocity couplet really started to tighten up. The following two images are the two subsequent scans.