Help---showing over 130 kts gtg shear!

[ericjkelly]

Hey guys!

Ok so I am reading the nowcast for today and someone posted on a tornadic cell and said that its "showing over 130 kts gtg shear. My question is HOW do they know that? Can I see that on Grlevel3? How?

Help

 

[Jesse Risley]

Hey guys!

Ok so I am reading the nowcast for today and someone posted on a tornadic cell and said that its "showing over 130 kts gtg shear. My question is HOW do they know that? Can I see that on Grlevel3? How?

Help

If you look at the storm relative velocity radar image (see this link), you'll notice the (KTS) showing outbound (red) and inbound (green) wind shear, which represents gate-to-gate shear, depicted as a velocity couplet. So, for example (I didn't see it), you could have had outbound winds of 70kts (red) synchronous with inbound winds of 60kts (green), yielding gate-to-gate shear of 130kts on that cell.

 

[ericjkelly]

Awesome! Thanks!

but how do you get the numbers 60 or 70kts etc?

 

[Jesse Risley]

Awesome! Thanks!

but how do you get the numbers 60 or 70kts etc?

Look at the legend on the left-hand side of the screen, or place the mouse over the velocity couplet in an active window of the program and it will display the velocity data in the bottom right-hand corner of the software.

 

[Chance Metz]

I know that on NWS radar they have a legend with certain color values that mean a certian amount of knots. Anything in the green is moving towards the radar anything red is moving away. Light red means 50 knots outbound while light green means 50 knots outbound. That would give you 100 knots total. I might have the two backwards but you get the point.

 

[rdale]

Light red means 50 knots outbound while light green means 50 knots outbound.

Nope, green is inbound usually. And they don't mean 50 knots either, it depends on the chosen color table.

 

[Chance Metz]

I thought that was wrong. Guess the colors only work for NWS radar and not all of them either.

 

[jshields]

i was the one that posted the storm was showing over 130 kts of gate to gate shear. i included a save of the radar image at that time. the bright red next to the bright green is the couplet actually showing 75 kts inbound, next to 75 kts outbound, so it's actually probably closer to 150 kts of gate to gate shear! there is a purple triangle which is a tvs signature over the spot where the two different colors are next to each other. when you're looking at live radar and you drag your mouse over the tvs signature, it will give you lots of info. i used the "lldv" number which is low level delta velocity. i've been told that's the gate to gate shear as well, and that number was 136 kts on this storm at that time!!

 

[Tim Shriver]

Be sure to look at all the SRV levels too. Does it penetrate the lower levels or
is it only at the higher tilts. Comparing different radars sites SRVs will also
help you get a better handle on things.

Also SRV works better the closer to the radar source.

Gate to gate is important as to the likelihood of tornado formation and also the
strength of the rotation.

As we witnessed here in WI just a little while ago shear is a very critical indicator.
Strong shear can make up for many other indicators that may be lacking or
lower then one would expect for tornado formation.

Tim

 

[Bart_Comstock]

I thought that was wrong. Guess the colors only work for NWS radar and not all of them either.

Chance, do you just mean the radar on the website for the NWS? Most sources that show radar images, including many local stations and the GRlvlX programs are getting their radar feeds from the NWS. Color tables can be set by the user and will vary from source to source even if they are using the same radar site. Don't try to base your gate to gate off the colors as you will find that this will not be accurate when jumping from website to website to get your radar information. Furthermore it may be hard to distinguish the different shades of color from one another and one color might represent multiple speeds (for example, "light green" = 40-42kts).

The way Tim, jshields, and Jesse suggested arethe more accurate and proper way of obtaining what the gate to gate speed is on your own.

 

[jshields]

WOW! this could go in the reports section, but i wanted to link it up to this thread. apparently there was a tornado that touched down in the same area of the couplet on the radar and it was rated an EF-4 with winds up to 170 mph!! i guess the radar was right

i was the one that posted the storm was showing over 130 kts of gate to gate shear. i included a save of the radar image at that time. the bright red next to the bright green is the couplet actually showing 75 kts inbound, next to 75 kts outbound, so it's actually probably closer to 150 kts of gate to gate shear! there is a purple triangle which is a tvs signature over the spot where the two different colors are next to each other. when you're looking at live radar and you drag your mouse over the tvs signature, it will give you lots of info. i used the "lldv" number which is low level delta velocity. i've been told that's the gate to gate shear as well, and that number was 136 kts on this storm at that time!!

 

[Jennifer Palmer]

Thanks for the explanation, guys!

This was one of those topics that came up the other night when I was watching those storms on radar, and I realized I had never learned how to figure that out!

I found this thread and another one here, and BAM! I learned something!

Thanks for explaining it!