Max Az Shear?

[JP Santiago]

I'm watching the storms just to the west of Kerrville, Texas, this afternoon on Google Earth using the interesting doppler overlays and there's one overlay I haven't been able to find an explanation for- what is the max az shear overlay/mode looking at? In past storms I've noticed that it seems to correlate with storms that have a high potential for tornadoes and I can only surmise that the feature has to do with measuring some parameter having to do with rotation/shear.

For instance, I noticed the bright red hues on that supercell that hit Salina, Kansas at the beginning of the month on the max az shear overlay. Before long, that cell dropped those tornadoes northeast of Salina.

EDIT: 20 minutes later or so, that same storm is tornado-warned.

 

[Kevin Scharfenberg]

Hi JP,

The product you're displaying comes from the azimuthal shear (shear between azimuths at approximately constant range) calculated from the linear least squares derivative of each radar's velocity field. Here is a link to a paper describing the technique and the product: http://ams.confex.com/ams/pdfpapers/64420.pdf

This product displays the strongest value of cyclonic shear in the lowest 2 km over the last 2 hours (I think)...so you can see roughly the path of low-level mesocyclones and other low-level shear features. Right now this is subject to problems from dealiasing failures and other data quality issues that we're working on to make the products more clean.

 

[Ryan McGinnis]

I'm watching the storms just to the west of Kerrville, Texas, this afternoon on Google Earth using the interesting doppler overlays and there's one overlay I haven't been able to find an explanation for- what is the max az shear overlay/mode looking at? In past storms I've noticed that it seems to correlate with storms that have a high potential for tornadoes and I can only surmise that the feature has to do with measuring some parameter having to do with rotation/shear.

For instance, I noticed the bright red hues on that supercell that hit Salina, Kansas at the beginning of the month on the max az shear overlay. Before long, that cell dropped those tornadoes northeast of Salina.

EDIT: 20 minutes later or so, that same storm is tornado-warned.
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Okay, I can't be the only guy who wants to know where one can find doppler overlays of this kind for Google Earth... Where'd you find that?

 

[Jeff Snyder]

Ryan,

See Google Earth and WDSSII

 

[JP Santiago]

This product displays the strongest value of cyclonic shear in the lowest 2 km over the last 2 hours (I think)...so you can see roughly the path of low-level mesocyclones and other low-level shear features. Right now this is subject to problems from dealiasing failures and other data quality issues that we're working on to make the products more clean.
[/b]

Thanks for the information and the link, Kevin. The Google Earth products you guys have come up with are very nice and great educational tools to show the non-weather geeks in the family/friends circle interesting features. I had noticed from reading everyone's posts to a given "NOW" thread in the Chase Forecasts section that the same cells everyone was looking at using subscription products, etc. that were tornadic were roughly correlating with the bright red colors I was seeing on the max az shear overlay. Having a TVS marker like other places show would be great, but now that I understand the az shear priniciple, it sorta does the same thing.