Reducing biases in estimates of precipitation over the United States: Phase 3 adjustments

Adjustment procedures for reducing the bias in precipitation point measurements of standard U.S. rain gauges are discussed. The procedures presented here employ information about wind speed variations over the gauge orifice during precipitation events and extensive metadata files which trace the history of precipitation measurements at each site throughout the period of instrumental observations (gauge type, exposure, and site climatology). The metadata required for this more sophisticated method has been compiled for about 1500 U.S. stations. A description of this metadata is provided, and examples of the application of this adjustment procedure are shown. However, reconstruction of precipitation over rough terrain from a network of adjusted point precipitation values still remains a problem for further studies.