Question about hodograph from April 3, 1974

[Jim Tang]

Of particular interest is the BNA hodograph.

This is from Corfidi's 2004 presentation on the event:
BNA 12Z-00Z Hodographs

Pay careful attention to the 18Z hodograph. Notice that 0-3 km SRH is over 1,000! Even more strangely though, look at the storm motion. From 12-18Z, it is at 98 kt! Is this is error?

A NWS meteorologist on another board pulled up the same hodograph with RAOB, and the 0-3 km SRH he got was only around 300.
http://www.easternuswx.com/bb/index.php?s=&showtopic=139724&view=findpost&p=2056552

 

[afischer]

The computed SRH may well be correct based on the storm motion, but yeah... storms on 04/03/74 were moving at more like 45-65kts.

 

[Jeff Snyder]

I assume you're looking at the loop of the hodograph (link: http://www.spc.noaa.gov/publications/corfidi/74outbreak_slides/74hodo.gif ). At 12z and 18z, it shows storm motion (probably user-defined, I can only assume) at 98kts, dropping to 48kts by 00z. I think the pink circled-x is the software-calculated right-mover storm motion based on the hodograph. At 12z and 18z, this storm motion marker is located near a magnitude of 18 kts and 38 kts, respectively. If the SRH noted on the right side is indeed that based on the 98 kts storm motion, then the calculated SRH will be in very large error. The large white cricled-x only shows up on the 00z hodograph. Interestinly, the position of the big white circle-x on the 00z hodograph looks correct for the storm motion noted on the right (48 kts). As such, I think the large white circled-x is probably at 98kts on the 12z and 18z hodographs, which places it beyond the hodograph window (which is why it doesn't show up on the 12z and 18z soundings)... This is just conjecture, though.

I made a hodograph using the Plymouth State archived data HERE. The * marks the estimated right-moved storm motion I believe, which matches up very well with the light pink circled-x on the Corfidi grpahics. The SRH on that hodograph shows ~489 m2/s2 (I think HEL on the right side is SRH, though it may be environmental helicity, equivalent to SRH if the storm motion is 0 ms-1). This compares pretty well with the big white-x on Corfidi's 00z hodograph, which lists ~352 m2/s2 (the difference looks to lie in the possibility that the big white crossed-x on Corfidi's hodograph lies closer to the wind profile, and therefore is less deviant, than that shown on the Plymouth State-made hodograph link to above). Unfortunately, I couldn't pull up the 18z sounding on Plymouth State. Though the 18z hodograph looks a little more curved, it doesn't look curved enough for the SRH to be more than double and nearly triple the SRH shown on the 00z hodograph.

Try sending a nice email to Corfidi to see what he says (I don't think he's a member here).