The soil moisture control section is not dry in any part for around 90 days in the udic moisture regime. The soil moisture control section becomes udic if the mean soil temperature is lower than 22 °C and the mean summer and winter soil temperatures (at a depth of 50 cm from the soil surface) differ by 6 °C or more, is dry in all parts for less than 45 consecutives days in the 4 months following the summer solstice. Soils that have an udic moisture regime commonly occur in areas of humid climates that have well distributed rainfall: i.e. they have adequate summer or winter rains, and generally cool summers