The moisture content of cotton at time of harvest has a direct effect on cotton quality. Weather, in particular relative humidity, strongly influences variation in cotton moisture content. This paper summarizes three years of observations of weather in and around cotton fields at harvest time in the Mississippi Delta.

Detailed studies of the variation of relative humidity, temperature, wind, sunlight, dew, and evaporation have been made in leafed fields and in fields where leaves were removed artificially. Single weather variables and combinations of variables have been related to dew intensity and to the rate of evaporation. Surface weather maps are presented to show the average pressure patterns associated with extremes in dew and evaporation. A preliminary cotton picking guide, developed jointly by the Weather Bureau and the Cotton Harvesting Section of the U.S. Department of Agriculture, which gives the farmer all objective estimate of when to start picking cotton on the basis of weather variation, illustrates how weather information can improve farm efficiency.