Variations of cloudiness, precipitable water, and relative humidity over the United States : 1973-1993

Water vapor variables were calculated from radiosonde stations in each of six U.S. regions for which cloudiness observations were available. Associations among variations of cloudiness, precipitable water and relative humidity during the 1973–93 period over the U.S. as a whole and in the six regions were determined. Trends in the quantities as well as relations among seasonal variations have been examined. There was a general increase in precipitable water in each season and in each region and a suggestion of increases in relative humidity. These were not accompanied by a general increase in cloudiness that was significant. However, there were significant correlations between seasonal anomalies of cloudiness and both relative humidity and precipitable water.