A high degree of correlation is shown to exist between the mean water equivalent of the snow pack on March 1 at snow courses in the Snake River region and the mean annual precipitation at nearby precipitation stations. Attempts were made to improve the correlation by introducing various additional parameters, but the resulting changes were not significant. In attempting to introduce length of snow‐accumulation season as a parameter, a relation between elevation, latitude, and average beginning date of continuous winter snow cover with at least one inch of snow on the ground was developed.

To aid in planning and design of additional flood protection on the Lower Rio Grande, the Hydroraeteorological Branch prepared a probable maximum precipitation study for the International Boundary and Water Commission (United States and Mexico) and the Republic of Mexico. Five drainages from 2,000 to over 17,000 square miles in area between Falcon and Anzalduas Dams including Rio San Juan and Rio Alamo in Mexico are the areas of concern. The great rains of hurricane Beulah, September 19–24, 1967 verified that additional protection is needed. Procedures for estimating probable maximum precipitation (PMP) are described. A particular problem was to estimate rainfall potential for the Sierra Madre Oriental in Rio San Juan and Alamo drainages. These mountains form a north‐south windward‐facing slope and barrier of over 7000 feet in elevation. A detailed study was made of rains from hurricane Beulah. The storm produced the greatest known rain depths in North America for 50,000 square miles or greater, and durations longer than 48 hours.