A 1 megaton nuclear weapon produces about 4*10^15J. How much mass must vanish when a 5 megaton weapon explode?

The density of a liquid could be found by using

The freezing and boiling point of a substance changes as the air pressure around it changes. for example, at a lower air pressure (higher altitude) it is easier for water molecules to escape from liquid into the air. in a high altitude city such as denver, colorado compared to a sea-level city such as houston, texas, water

Looking at this barometer, is the air pressure high or low? what type of weather would you expect? high, bad low, bad high, good low, good