In Piper's sole three chapters of HoH, Khione, Greek goddess of snow, attacks the group of demigods as they sail across the Mediterranean toward Epirus. Her presence alone is enough to cause freezing rain. Freezing rain occurs when the surface temperature is 0 Celsius or lower, yet either higher atmospheric temperatures or atmospheric pressures aren't suitable for snow.
She also passively churns the sea and summons a storm cloud large enough that Piper can no longer see the sky, but meh
Anyway, her effects extend all the way to the horizon going by the narrative.
Piper is standing above deck on the Argo II, which is tall enough to fit the 12.8m Athena Parthenos statue in only the stables.
Distance to horizon formula is d=3.57*sqrt(h).
d=3.57*sqrt(12.8)
d=12.77242km
According to the chart in the linked Wikipedia page, our height would extend up to about 2.3 kilometers and our temperatures range from -2 to about 4 degrees C. I will use 4 uniformly.
But as for the affected volume...
vcylinder=pi*r^2*h
v=pi(12772.42/2)^2*2300
v=925793169852.33m^3
Apparently, cruises in the Mediterranean can expect 86-88 degrees F at sea. That's around 30 degrees C.
Density of air in 30 degree temperatures is about 1.1644 kg/m^3.
925793169852.33*1.1644=1077993566976 kg
So Khione basically dropped this mass of air from 30 degrees to 4 degrees or less, or a change in temperature of 26 degrees.
Specific heat capacity for air between 40 degrees and -50 degrees is 1.005.
Q=specific heat capacity*mass*change in temp
Q=1005*1077993566976*26
Q=28167971905082880J
or about 6.7 megatons.
Really, that figure should be negative, but that's just indicating that she sapped this energy rather than put it into the atmosphere.
Anyway, Khione's doing this so passively that she hasn't even arrived in the Mediterranean yet. When she does, it starts snowing and hailing and Piper notes that the temperature drops so drastically so quickly that her "ears pop" and her body starts to freeze.
Leo Valdez using his pyrokinesis was able to overpower a direct attack from Khione and make the surrounding area nice and toasty.
