The 1-day Average 4-inch Bare Soil Fractional Water Index map displays the 24-hour-averaged soil moisture at 4 inches (10 cm) under bare soil for the previous day. Fractional water index ranges from 0 (as dry as the sensor can read) to 1.0 (as wet as the sensor can read). Soil moisture cannot be measured if the soils are frozen. This may cause our maps to have large areas of missing data during the winter months. This map is updated once each day between 7 and 8 AM.