What causes variations in precipitation?

The air that is moving around us brings denser or less dense clouds, causing more or less precipitations. read more

As a warm front passes, you can expect a slow rising of the warmer moist air and a drizzle that goes into a constant rain out of nimbostratus clouds. But when the cold front moves is, the air is much more unstable and it causes isolated cumulonimbus that causes rain showers separated by spell of clear sky. read more

Furthermore, for the first time in the U.S. National Climate Assessment, a confidence statement is made that some projected precipitation changes are deemed small. It is incorrect to attempt to validate or invalidate climate model simulations of observed trends in these regions and/or seasons, as such simulations are not designed to forecast the precise timing of natural variations. read more

Daily Variations. Rainfall is more likely at certain times of the day in some regions (Sections 7.4 and 9.5). Convective rainfall often has a pronounced diurnal rhythm, especially on tropical islands. On land, it is most common in the afternoon after the surface has been heated by the Sun. read more