Matt has given the ok to use the anime version so here I go
Here are all the images for scaling
And here we can see that Kobayashi's apartment has four floors and that Tohru's dragon form is about as tall as Kobayashi's apartment.
((233.5*4) + 79.6)*2 = 2027.2 cm or 20.27 meters. Plug that into the horizon calculator and you get yourself 16.1 km or 16100 meters. I'll use 12 km or 12000 meters for the height of the clouds and it took about 7 seconds for us to see the clear sky. Also cloud density is 1.003.
KE = 0.5 x 1.003 x 12000 x pi x (16100^4)/(7^2) = 3.7034923e+18 joules but then I gotta divide by 7 since it took her seven shots.
That gets me 3.7034923e+18 joules or Mountain level+
This would scale to Kanna's AP
Redux of the Redux
Everyone seems to agree with using 2 km instead of 12 km. I also used the frame-by-frame feature on Premiere Pro to get an exact timeframe.
KE = 0.5 x 1.003 x 2000 x pi x (16100^4)/(5.07^2) = 8.2364182e+18
8.2364182e+18/7 = 1.1766312e+18 joules or 281 megatons or Mountain level