RHI cross section of through two thunderstorms at (a) 0001:31 UTC 18 April and (b) 0112:20 UTC 13 May 1995. Radar reflectivity and Doppler velocity are shown on the top and bottom of each figure, respectively. A prominent curl in reflectivity is shown by the white arrow in (a). The location of a rotational couplet along a horizontal axis is shown by the white arrow in (b). Range rings and azimuths are every 10 km and 30 degrees, respectively. Schematic diagrams of the flow patterns are shown in the middle of (a) and (b).The gray shading in the schematic represents reflectivities greater than 15 DBZ.

The key feature of figure a is the pronounced curl of echo that not only protrudes into the Weak Echo Region (WER) but wraps completely around. This feature has not been elucidated in the past studies of WERs. The strong rotational couplet in figure b has a velocity difference of ~75 m/s ( 30 m/s away and 45 m/s toward the radar, respectively). This curl/rotational couplet may play a key role in hail growth.