CONTENTS Preface...... ii Chapter 1. Basic Data Daily data - Hourly data - Six-hourly data - Representativeness of observations Chapter 2. Probable Maximum Precipitation Introduction - Maximum observed precipitation - Seasonal distribution of maximum precipitation - Meteorological situations associated with heavy precipitation - Mois- ture adjustment of storm precipitation - Precipitation-moisture ratio (P/M) - Com- putation of PMP - Chronological distribution - Appraisal Chapter 3. Rainfall-Frequency Data Basic data - Frequency analysis - Isopluvial ma.ps - Smoothing data read frcm the map Depth-area relationships - Seasonal variation References LIST OF ILLUSTRATIONS Figure No. Pane 1.- 1. Precipitation stations 1 - 2. Area and station elevation curves 2 - 1. Adjusted maximum observed 24-hr. precipitation 2 - 2. Surface synoptic map for 1200 GMT, October 23, 1954 2 - 3. Surface synoptic map for 1200 GMT, June 13, 1963 2 - 4. Surface synoptic map for 1200 GMT, August 29, 1954 2 - 5. Surface synoptic map for 1200 GMT, October 23, 1951 2 - 6. Comparison of precipitable water estimated from surface dew points with that observed in soundings (maximum dew points) 2 - 7. Comparison of precipitable water estimated from surface dew points with that observed in soundings (maximum moisture) 2 - 3 -. 60-yr. 12-hr. persisting dew points for mid-July 2 - 9. 50-yr. 12-hr. persisting dew points for mid-October 2 - 10. Variation of P/M ratio with elevatiun 2 - 11. Moisture inflow barriers 2 - 12. Probable maximum 24-hr. point precipitation 2 - 13. Probable maximum 6-hr. point precipitation 2 - 14. Depth-duration diagram for 6- to 24-hr. PMP 2 - 15. Depth-area-duration diagram for PMP for durations under 6 hours 2 - 16. Depth-area curves for PMP for durations fromm R to 24 hours 2 - 17. Ratio of probable maximum 6-hr. pree p tation to 100-yr. 6-hr. rainfall 3 - 1. Duration-interpolation diagram 3 - 2. Return-period-interpolation diagram 3 - 3. Variation of 2-yr. 24-hr. rainfall with elevation - southern California coastal mountains and Cascade Range 3 - 4. Relation for adjusting 2-yr. 24-hr. rainfall data for elevation 3 - 5. Points for which probable maximum precipitant on and rainfall- frequency data were computed 3 - 6. Diagram for e.st.imating 2-yr. 1-hr. amounts. 3 - 7. Mean annual number of thunderstorm days 3 - 3 -. Smoothing values read from isopluvinl maps 3 - 9. Depth-area curves for rainfall-frequency data 3 - 10. Monthly distribution (in percent) of 24-hr. rainfalls for various return periods Figure No. 3 - 11. 1-yr. 30-min. rainfall 3 - 12. 2-yr. 30-min. rainfall 3 - 13. 6-yr. 30-min. rainfall 3 - 14. 10-yr. 30-min. rainfall 3 - 15. 25-yr. 30-min. rainfall 3 - 16. 50-yr. 30-min, rainfall 3 - 17. 100-yr. 30-min. rainfall 3 - 13. 1-yr. 1-hr. rainfall 3 - 19. 2-yr. 1-hr. rainfall 3 - 20. 5-yr. 1-hr. rainfall 3 - 21. 10-yr. 1-hr. rainfall 3 - 22. 25-yr. 1-hr. rainfall 3 - 23. 50-yr. 1-hr. rainfall 3 - 24. 100-yr. 1-hr. rainfall 3 - 25. 1-yr. 2-hr. rainfall 3 - 26. 2-yr. 2-hr. rainfall 3 - 27. 5-yr. 2-hr. rainfall 3 - 23. 10-yr. 2-hr. rainfall 3 - 29. 25-yr. 2-hr. rainfall 3 - 30. 50-yr. 2-hr. rainfall 3 - 31. 100-yr. 2-hr. rainfall 3 - 32. 1-yr. 3 -hr. rainfall 3 - 33. 2-yr. 3 -br. rainfall 3 - 34. 6-yr. 3 -hr. rainfall 3 - 35. 10-yr. 3-hr. rainfall 3 - 36. 25-yr. 3 -hr. rainfall 3 - 37. 50-yr. 3 -hr. rainfall 3 - 38. 100-yr. 3-hr. rainfall 3 - 39. 1-yr. 6-hr. rainfall 3 - 40. 2-yr. 6-hr. rainfall 3 - 41. 5-yr. 6-hr. rainfall 3 - 42. 10-yr. 6-hr. rainfall 3 - 43. 25-yr. 6-hr. rainfall 3 - 44. 50-yr. 6-hr. rainfall 3 - 46. 100-yr. 6-hr. rainfall 3 - 46. 1-yr. 12-hr. rainfall 3 - 47. 2-yr. 12-hr. rainfall 3 - 48. 5-yr. 12-hr. rainfall 3 - 49. 10-yr. 12-br. rainfall 3 - 50. 25-yr. 12-hr. rainfall 3 - 51. 50-yr. 12-hr. rainfall 3 - 52. 100-yr. 12-hr. rainfall 3 - 53. 1-yr. 24-hr. rainfall 3 - 54. 2-yr. 24-hr. rainfall 3 - 55. 5-yr. 24-hr. rainfall 3 - 56. 10-yr. 24-hr. rainfall 3 - 57. 25-yr. 24-hr. rainf.all 3 - 58. 50-yr. 24-hr. rainfall 3 - 59. 100-yr. 24-hr. rainfall