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 Hgt 50dBZ = 20,345 ft AGL TBSS length = 8 nm POSH = 50 % MEHS = 1 ¼ “ (250%) MLT = 11,180 ft AGL WBZ = 9,849 ft AGL RH mb = 33 % Max Obs. Hail = ½ “ *** Next five sets of images are all the at same scale

#2 – 11 August 2005, 0214z Max Ref = 70 dBZ Hgt 50dBZ = 31,590 ft AGL TBSS length = 12 nm POSH = 90 % MEHS = 2 ½ “ (143%) MLT = 11,180 ft AGL WBZ = 9,849 ft AGL RH mb = 33 % Max Obs. Hail = 1 ¾ “

#3 – 25 July 2005, 0438z Max Ref = 65.5 dBZ Hgt 50dBZ = 33,689 ft AGL TBSS length = 8 nm POSH = 80 % MEHS = 2 ¼ “ (225%) MLT = 13,322 ft AGL WBZ = 9,885 ft AGL RH mb = 19 % Max Obs. Hail = 1 “

#4 – 25 July 2005, 0453z Max Ref = 65.5 dBZ Hgt 50dBZ = 33,931 ft AGL TBSS length = 10 nm POSH = 70 % MEHS = 2 “ (400%) MLT = 13,322 ft AGL WBZ = 9,885 ft AGL RH mb = 19 % Max Obs. Hail = ½ “

#5 – 20 July 2005, 2224z Max Ref = 66.5 dBZ Hgt 50dBZ ≥ 31,500 ft AGL TBSS length = 9 nm POSH = 70 % MEHS = 2 “ (73%) MLT = 12,133 ft AGL WBZ = 10,911 ft AGL RH mb = 23 % Max Obs. Hail = 2 ¾ “

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… Let’s look at one final case from 2004

#6 – 3 July 2004, 2128z Max Ref = 74.5 dBZ Hgt 50dBZ = 33,348 ft AGL TBSS length = 22 nm POSH = 100 % MEHS > 4 “ (400%) MLT = 9,153 ft AGL WBZ = 8,017 ft AGL *RH mb = 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)