Chapter 7: Part 622 Snow Survey and Water Supply Forecasting from the National Engineering Handbook

The U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Snow Survey and Water Supply Forecasting Program issues water supply forecasts for hundreds of points in the Western United States. The primary forecast product is a seasonal volume for a specified period of months (e.g., April–July). These forecasts are issued near the first of the month between January and June. Mid-month updates are also issued for selected forecast points. In addition, daily guidance forecasts are issued for a subset of forecast points using an automated procedure.

This chapter describes the essential features of water supply forecasting as practiced in the NRCS. The topics are presented in a roughly chronological sequence of activities, from forecasting point establishment, to data gathering, to model development, to operations, and finally to verification. Citations of foundational professional literature and NRCS technical notes are given to provide sources of details on mathematical procedures and other technical information not explicitly described in this chapter.