Gregg was born on January 4, 1880, in Phoenix, New York, the oldest of six children of Willis Perry and Jennie E. (Ray) Gregg and a descendant of James Gregg of Ayrshire, Scotland, who went to Ireland in 1690 and thence to America, becoming one of the founders of Londonderry, New Hampshire.
Following graduation from the Phoenix high school in 1898, young Gregg attended Cornell University, where he received his A. B. degree in 1903.
On March 1, 1904, Gregg entered the service of the United States Weather Bureau, to which his entire career was devoted. After three years at Grand Rapids, Michigan, and at Cheyenne, Wyoming, he was transferred to the research station at Mount Weather, Virginia, where important pioneer investigations of the upper air were being conducted under the direction of the physicist William R. Blair. As Blair's assistant, Gregg participated in kite observational work which contributed greatly to increased efficiency in weather forecasting and was the foundation of his own subsequent upper-air research. He remained at Mount Weather until 1914, when he left to act as meteorological observer of the Smithsonian Expedition to Mount Whitney, California. In November 1914 Gregg went to Washington, D. C. , as assistant chief under Blair of the Weather Bureau's newly established aerology section, a section that, with the increasing importance of aviation and the advent of World War I, was soon made a division. In 1917 Gregg became its chief, and soon thereafter its work was extended by funds specifically appropriated "for observing, measuring and investigating atmospheric phenomena in the aid of aeronautics. " Gregg himself considered that his division's most important function during the war was to provide data, information, and meteorological equipment for the United States army and navy services and to assist these services in setting up their own meteorological stations at a number of training fields. In May 1919 he acted as special meteorological adviser at Trepassey, Newfoundland, for the transatlantic flight of a group of United States Navy NC-class seaplanes, and in July 1919 he served in a similar capacity at Mineola, Long Island, for the crossing of the British dirigible R-34, two pioneering flights heavily dependent on accurate weather predictions. After the war Gregg's work centered in the growth of commercial aviation. His Aerological Division, which had the principal responsibility for providing weather services for commercial airways, had become by 1934 the largest division in the Weather Bureau. On January 31, 1934, Gregg succeeded Charles F. Marvin as chief of the Weather Bureau itself, a position he held until his death. During his administration he put into effect many of the recommendations of the Science Advisory Board, an independent group of scientists appointed in 1933 to make a study of some of the government's scientific bureaus, including the establishment of air-mass methods of weather analysis over the whole United States and the issuance of weather maps at six-hour intervals, thus providing more frequent data for forecasters. Professionally and in private life Gregg was well liked. Deeply rooted in his work, he spent many of his leisure hours in developing his own ideas for the improvement of meteorological science and in activities connected with the many scientific societies to which he belonged. He was the author of a monograph, Aerological Survey of the United States (2 vols. , 1922-1926), and a handbook, Aeronautical Meteorology (1925; 2nd ed. , 1930). He served the American Meteorological Society for fifteen years as treasurer and became its president in 1938. He was also chairman of the executive committee and of the subcommittee on meteorological problems of the National Advisory Committee for Aeronautics, chairman of the section of meteorology of the American Geophysical Union, and president of Regional Commission IV (North America, Central America, West Indies) of the International Meteorological Organization. Gregg died of a coronary thrombosis on September 14, 1938, while attending an aviation conference in Chicago and was buried in Rock Creek Cemetery, Washington, D. C.
President of the American Meteorological Society (1938), president of Regional Commission IV of the International Meteorological Organization
Gregg was survived by his wife, formerly Mary Chamberlayne Wall, daughter of a clergyman in Berryville, Virginia, whom he had married on October 15, 1914, and by their adopted daughter, Ruth Marguerite.
