Climate is day to day, year to year, weather. Climatology is the study of the variations (and consistencies) in our weather. The Climate of Iowa is being published in a continuing series of parts, each of which treats a specific weather element or problem in some detail. The weather condition affecting a given activity is defined briefly and the probability of occurrence of this condition (the risk involved) is estimated for several localities in Iowa and for different seasons. When practical, suggestions are offered for improving or utilizing unfavorable weather conditions. Specific applications of climatological techniques at Iowa State are concerned primarily with agricultural problems but, in many cases, application to industrial, engineering or human endeavor is direct and such application is encouraged wherever possible.