Pixel Scaling[]
A Nimbostratus cloud is at least 2000 m thick
Storm height: 2000*(546/453) = 2410.59602649 m
Calculation[]
Radius: 2410.59602649*737/[546*2*tan(70deg/2)] = 2323.49907499 m
Area: 16960353 m^2
Cloud does not appear to be floating any distance above surface as this is Hill Top Zone
Mass: 44620086620.79779 kg
Using weak instability (1000 J/kg)
44620086620.79779*1000 = 4.4620087e+13 Joules
Tally[]
Chaos Emerald creates a storm: 10.66 Kilotons; Town level