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1. INTRODUCTION Forecast precipitation and runoff on time scales fyom several hours to several days in advance can be critical to the reservoir operators' decision-making process. Currently, the NWS (National Weather Service) provides QPF (quantitative precipitation forecasts) out to 24 h into the future. In addition to the QPFs, 2- to 3-d precipitation outlooks are also available. However, the NWS products do not adequately address orographic (mountain- induced) precipitation, which is the most significant contributor to wintertime precipitation in most watersheds and river basins of interest to Reclamation (Bureau of Reclamation), Given the large variability in precipitation (frequency, amount, and type) and subsequent runoff in mountainous areas of the Western United States, managing reservoir operations optimally is difficult. Better QPFs extending further into the future are needed. The research study summarized in this report addresses the problem of inaccurate and untimely QPFs. The study was funded under the Research and Laboratory Services Division's WATER (Water Technology and Environmental Research) Program. The end objectives for this study were to develop the methodology for more accurate and timely wintertime QPFs for mountainous watersheds and river basins of interest to Reclamation, then integrate the QPFs with existing hydrologic headwater runoff models to improve forecasts of runoff (amount and timing) and the potential for flooding. More accurate and timely headwater runoff forecasts will improve Reclamation's effectiveness in making operational decisions for water resources management and reservoir operations. This summary report is separated into two parts, which are located in sections 2 and 3. The first part summarizes the research related to combining existing orographic (mountain- induced) precipitation and runoff models for improving reservoir operations. The study area was the American River Basin in the Sierra Nevada of northern California. This area experiences occasional relatively warm winter storm episodes of heavy precipitation which produce flooding potential. Models used in the study were the 2-D (two-dimensional) orographic precipitation model developed by Rhea (1978), and the HED71 headwater runoff forecast model (Buer, 1988) developed by the NWS's CNRFC (California-Nevada River Forecast Center) and the CDWR (California Department of Water Resources). The second part of the report is an assessment of how applied research within Reclamation, particularly in the area of better QPFs and flood potential forecasts, might improve Reclamation's water operations. Because Reclamation water operation managers are and will continue to receive hydrologic forecasts from the NWS, future meteorological applied research will require collaboration between Reclamation and NWS personnel so that Reclamation's work will result in added value to NWS products. 2. COMBINING OROGRAPHIC PRECIPITATION AND RUNOFF MODELS FOR IMPROVING RESERVOIR OPERATIONS 2.1 Orographic Precipitation Model Description The orographic precipitation model is a simple 2-D model, originally developed by Dr. J. Owen Rhea in the mid-1970s for western Colorado, for both climatological purposes and as a QPF (Quantitative Precipitation Forecasting) aid. This section only provides a brief description of the precipitation model; a complete description is given in Rhea (1978).