# Presentation: 707638

## An Update on TBSSs and Relatively Moist Environments

- Matthew J. Bunkers
- 2006 Spring Training

## Three-Body Scatter Spike (TBSS)

## TBSS Review

- Radar artifact typically associated with hail ≥ 1”(high POD and low FAR)
- Observed down-radial of ~62+ dBZ core(use 4-panel and/or all-tilts displays)
- May also indicate potential for damaging winds?
- More at P:\Training\8thGreatDivide\TBSS

## Recent Trends

- At least two events in 2005 with TBSSs but only limited, or no, severe hail
- Another case around the same time with TBSSs and very large hail
- What’s going on here?

## #1 – 10 August 2005, 2130z

- Max Ref = 68.5 dBZ
- Hgt50dBZ = 20,345 ft AGL
- TBSS length = 8 nm
- POSH = 50 %
- MEHS = 1 1⁄4 “ (250%)
- MLT = 11,180 ft AGL
- WBZ = 9,849 ft AGL
- RH700-300mb = 33 %
- Max Obs. Hail = 1⁄2 “

- *** Next five sets of images are all the at same scale

## #2 – 11 August 2005, 0214z

- Max Ref = 70 dBZ
- Hgt50dBZ = 31,590 ft AGL
- TBSS length = 12 nm
- POSH = 90 %
- MEHS = 2 1⁄2 “ (143%)
- MLT = 11,180 ft AGL
- WBZ = 9,849 ft AGL
- RH700-300mb = 33 %
- Max Obs. Hail = 1 3⁄4 “

## #3 – 25 July 2005, 0438z

- Max Ref = 65.5 dBZ
- Hgt50dBZ = 33,689 ft AGL
- TBSS length = 8 nm
- POSH = 80 %
- MEHS = 2 1⁄4 “ (225%)
- MLT = 13,322 ft AGL
- WBZ = 9,885 ft AGL
- RH700-300mb = 19 %
- Max Obs. Hail = 1 “

## #4 – 25 July 2005, 0453z

- Max Ref = 65.5 dBZ
- Hgt50dBZ = 33,931 ft AGL
- TBSS length = 10 nm
- POSH = 70 %
- MEHS = 2 “ (400%)
- MLT = 13,322 ft AGL
- WBZ = 9,885 ft AGL
- RH700-300mb = 19 %
- Max Obs. Hail = 1⁄2 “

## #5 – 20 July 2005, 2224z

- Max Ref = 66.5 dBZ
- Hgt50dBZ ≥ 31,500 ft AGL
- TBSS length = 9 nm
- POSH = 70 %
- MEHS = 2 “ (73%)
- MLT = 12,133 ft AGL
- WBZ = 10,911 ft AGL
- RH700-300mb = 23 %
- Max Obs. Hail = 2 3⁄4 “

## What does this show?

- Not much difference up to this point...
- Similar max reflectivity, TBSS lengths, and MLT/WBZ levels
- Generally small-to-moderate storm cores
- Is there a pattern in the moisture field that can help explain this?

## #1 – 10 August 2005, 2131z (wv sat)

## #2 – 11 August 2005, 0215z (wv sat)

## #3,4 – 25 July 2005, 0445z (wv sat)

## #5 – 20 July 2005, 2224z (wv sat)

## From AWOC...

- Recall that a moist atmosphere can accelerate the hail melting process
- Flash presentation... http://www.wdtb.noaa.gov/courses/awoc/ICsvr1/ICSvr1-lesson3/ic1-lesson3_color/
- Let’s look at one final case from 2004

## #6 – 3 July 2004, 2128z

- Max Ref = 74.5 dBZ
- Hgt50dBZ = 33,348 ft AGL
- TBSS length = 22 nm
- POSH = 100 %
- MEHS > 4 “ (400%)
- MLT = 9,153 ft AGL
- WBZ = 8,017 ft AGL
- *RH700-300mb = 50 %
- Max Obs. Hail = 1 “

- *** Note this is at a smaller scale than the previous radar images

- Produced flash flooding and copious small hail

## 03 July 2004, 2115z (wv sat)

## Summary

- Phone logs indicate these storms with TBSSs and sub-severe to marginally severe hail produced very heavy rainfall and copious small hail
- Some of these storms were supercells, but still struggled to produce very large hail
- The best discriminator for these events may be the water vapor imagery

## Summary

- The length of the TBSSs were below average, based on J. Johnson’s local study(however the last event was 22 nm)

## Summary

- The SOO proposes an additional CTA for severe thunderstorm warnings to account for these kinds of events/environments...
*  “**This storm is capable of producing a lot of small to moderate size hail and very heavy rainfall...possibly causing low lying roads to become covered with ice.”*
*    **(or something like this)*