Probably it is the large storm in center of the detailed images that attracts your attention first… Though even this storm exhibits an overall increase of the 3.7 µm reflectivity, as regards the magnitude of the increase it is well outweighed by the smaller, arrowed storm (in the ch3ref image it looks much darker than the big one). Notice that the arrowed storm exhibits the "cold-U", while the thermal IR field of the "big one" is significantly more complex, resembling a spiral with a "warm eye". (The big storm has created hailstones 5-6 cm in diameter.)