He began his career in weather during World War II. He worked for Admiral Chester Nimitz in the Pacific. Roberts was on the first plane to enter the eye of a tropical system near the Philippines. This method is still used today by the "Hurricane Hunters" of the Air Force based at Keesler Air Force Base in Biloxi, Mississippi to measure and record internal conditions in hurricanes in the Gulf of Mexico, the Caribbean Sea and Atlantic Ocean to help predict their development and path.
Nash continued as a local forecaster on New Orleans television and radio. His calm guidance during these storms made him legendary to people throughout southeast Louisiana. He was the only local forecaster to accurately predict the paths of Hurricane Betsy in 1965, which hit the New Orleans area directly, and Hurricane Camille in 1969, a storm that devastated coastal Mississippi.
After departing WDSU in late 1973, he moved to then-new Newscene 8 at WVUE-TV in February 1974 for 4 years, then to Eyewitness News at WWL-TV on March 20, 1978. As he aged, he gradually cut back his schedule, giving most of the day-to-day weathercasting chores to younger meteorologists Al Duckworth, who had been at WWL since 1968, and Dave Barnes.
In later years, Nash was the favorite forecaster in the area, especially among older viewers, to the point where competitors good-naturedly referred to him as "the Weather God". After his retirement, he would be brought back as a special consultant when hurricanes threatened in the Gulf. By the late 1980s he seemed to many like a figure from an earlier era, as he eschewed computer graphics and other modern special effects in favor of a simple black marker and paper map. Nash retired from the Eyewitness News anchor desk in February 1984, but would come back during storms to help calm and educate the locals during hurricane season, sometimes to the visible resentment of the station's younger weathermen,[who?] especially when Nash's experience, intuition, and pen and paper yielded more accurate predictions than their computer models. He accurately predicted the path of Hurricane Georges in 1998, while all the full-time on-air meteorologists of the area, namely Bob Breck of WVUE and Dan Milham of WDSU, predicted an incorrect track.
Roberts finally retired from even his special hurricane appearances in July 2001 (in part to help take care of his wife of over 60 years, Lydia), and that same year donated his papers to Loyola University, New Orleans.
He was fully retired, and had not been seen on TV in several years by 2006. Roberts and his wife evacuated in advance of Hurricane Katrina in 2005, the first time he had left town for a hurricane. Nash figures prominently in a 2006 book about Hurricane Camille, "Roar Of The Heavens," by Stefan Bechtel.