SRH do you use it when choosing targets?

tom hanlon

EF2
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Jun 12, 2004
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So I am adding to my forecasting tools and researching SRH and tornado formation. I am curious if anyone who actively chases storms takes a look at SRH ?

This paper highlights the significance.
http://www.crh.noaa.gov/grr/science/19800513/09.php

This paper does as well, it also adds LCL and the usual suspects into the mix. What I found here that I was not in the habit of checking was EHI. Curious if anyone looks at EHI in the skew-t when they are forecasting ?

Here is the paper.
http://64.233.167.104/search?q=cach...rm+relative+helicity&hl=en&ct=clnk&cd=7&gl=us

I look forward to other links on SRH , or opinions on its usefullness, same goes for EHI if anyone cares to discuss.

--
Tom Hanlon
 
SRH, or more properly, SREH, can be a useful tool. However, it is highly variable in both space and time. For example, in VORTEX, I believe SREH was calculated to be close to 1000 J/Kg in the inflow notch of a tornadic supercell, much higher than you'll usually see on NWP output maps. This fact means that what you see on NWP maps is very broad brush, and unlikely to be what a particular storm is ingesting. During large, synopitically evident outbreaks, forecasted SREH can be pretty useful - otherwise, it's something to be cautious of, IMO.
 
There can be a large variation in SREH for storms, certainly near a boundary, but using it as a forecast tool is highly valuable. Seeing a storm moving into an area of higher SRH should give you extra reason to worry about it. Noticing storms develop in regions with very low SRH (TX yesterday) makes you a little less excited about a big tornado event...
 
The folks at SPC have written a number of papers dealing with SRH, here is one of their latest:

http://www.spc.noaa.gov/publications/thompson/effective.pdf

You can find more of their work at the below link, and if you really want to dig deeper can follow some of their references to other articles:

http://www.spc.noaa.gov/publications/

**EDIT**

To answer the question in the title of the thread, I do use SRH when chasing, but always in context since it's important to determine when a region of high helicity is worth getting excited about and when it is not. Many times a helicity bullseye is simply an indication that a particular region is stable/strongly capped.
 
Building upon research done by the SPC and others, we look at SRH along with EHI and other parameters in a new tornado detection system called the BTI.

More info at:
http://www.baronservices.com/bti2/index.php

And yes, SRH is very useful for finding potentially tornadic storms, but you also have to look at CAPE as well. This is where the EHI works as a good metric (CAPE x Helicity / 160,000).
 
Storm relative helicity (especially 0-1km) can be helpful in determining areas favorable for rotating storms. While model output can help identify areas of high SRH, the SRH can vary greatly over a small distance. A localized area of backing winds at the surface associated with a boundary can rapidly increase the SRH. While this parameter is helpful, you need to be sure to look at moisture, instability, and CIN as well.

As mentioned by Matthew Havin - the EHI is a good parameter. The EHI shows the relationship between CAPE and SRH. High values of CAPE and low SRH can have the same effect as low CAPE and high SRH.
 
I usually glance at it, but don't use it much. I prefer to examine winds at each level, and I prefer other model products that may include SRH like EHI. A forecast sounding is a really nice tool, and provides more info IMO.

As for EHI (that you mention), I've always kind of liked it, and my impression is it is one of the big indices that SPC uses to help draw a broad Convective Outlook area as it show CAPE highlighted with related Helicity which are typically two things required for severe.
 
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