The elements composing a are combined in a definite proportion by mass .

Law of Definite Proportions states that in a given type of chemical substance, the elements are always combined in the same proportions by mass. ... Oxygen makes up 88.8% of the mass of any sample of pure water, while hydrogen makes up the remaining 11.2% of the mass

if the temperature drops and becomes cool

then the atmosphere can be freezing as the water vapor in the air is at maximum (100%) and can be severely cold

also can be snowing lightly as the moisture in the air will start to solidify

and btw this is not chemistry but