Bill Gray: A Towering Figure in Hurricane Science

Famed hurricane research William Gray passed away at his home in Fort Collins, CO, on Saturday, April 16, 2016. His death came just as colleagues were gathering in San Juan, Puerto Rico, for the American Meteorological Society’s 32nd Conference on Hurricanes and Tropical Meteorology, a meeting that Gray had attended regularly since the 1960s. Gray’s best-known research contribution was his founding of seasonal hurricane prediction techniques, which both emerged from and led to a growing understanding of how phenomena such as El Niño and La Niña influence the likelihood of tropical cyclones. Gray published many dozens of peer-reviewed papers, mainly in tropical meteorology. Late in his career, Gray spoke out passionately against the global consensus on climate change science, as noted in a memorial published by Colorado State University (CSU)--Gray’s professional home for more than 50 years.

Figure 1. Bill Gray. Image credit: CSU.

Drawn to hurricanes in the Windy City
As a youth in Washington, D.C., Gray aspired to become a pro baseball player. That career path was derailed by a knee injury while Gray was an undergraduate student at George Washington University. Shifting career paths and locations, Gray joined the U.S. Air Force in 1953 and spent a year studying meteorology at the University of Chicago--then one of the nation’s leading focal points for atmospheric science, a still-small but fast-growing field at the time.

After several years as an Air Force forecaster, Gray returned to Chicago, completing his master’s degree in meteorology in 1959 and his doctoral degree in geophysical sciences in 1964. Gray was introduced to tropical meteorology by his eventual advisor and mentor, Chicago professor Herbert Riehl. Gray completed his dissertation on internal stress characteristics and scales of motion within hurricanes. Data for that project came from reconnaissance flights into three 1958 hurricanes: Cleo, Daisy, and Helene. Gray himself participated in a flight into Helene.

Dr. Riehl left Chicago to found CSU’s Department of Atmospheric Science in 1960. Gray followed in 1961, remaining at CSU for his entire career. The two played a huge role in building CSU’s role--somewhat paradoxical for a campus near the Rocky Mountains--as a major center for tropical meteorology. Much like his Chicago colleague T. Theodore “Ted” Fujita (creator of the Fujita Tornado Damage Scale), Gray was first and foremost an observationalist who paid meticulous attention to data. While Fujita focused on processes within storms, Gray’s career eventually gravitated toward the larger-scale analysis of the regional and global environments that shaped hurricane activity. One of his primary insights was on the role of wind shear in controlling hurricane growth and decay. In his landmark 1968 paper “Global View of the Origins of Tropical Disturbances and Storms,” Gray published a detailed analysis of the globe’s favored regions for tropical cyclone activity, at a time when satellite imagery was in its infancy.


Figure 2. An analysis of origin points for tropical storms around the globe. Image credit: William M. Gray, “Global View of the Origins of Tropical Disturbances and Storms,” Monthly Weather Review 96, October 1968.

Developing the seasonal outlooks
It was the record-strong El Niño of 1982-83 that piqued Gray’s interest in seasonal hurricane prediction. Right from the start, the CSU forecasts were based on correlations among various factors found to be associated with Atlantic hurricane activity. Gray was the first to develop a formula that incorporated such processes into an estimate of how much activity an entire season might produce. Gray launched his technique by taking into account three factors: the quasi-biennial oscillation, the state of the El Niño-Southern Oscillation, and the departure from the seasonal average of sea level pressure across the Caribbean Sea. The technique gradually expanded to incorporate a wide array of other variables.

Gray’s first seasonal prediction--archived online, together with all subsequent outlooks--was published on May 24, 1984. “Until now,” he noted, “there has been no objective and skillful method for indicating whether a coming hurricane season was going to be an active one or not.” Perhaps sensing where the outlooks might lead, he added: “This paper has been prepared for the professional meteorologist, the news media, and any interested layman.” Gray issued forecasts each June and August from 1984 onward, adding April and December outlooks starting in 1995 and bringing in graduate student Phil Klotzbach in 2000. (Dr. Klotzbach became lead author of the outlooks starting in 2006.) The April 2016 outlook was released on April 14.

Despite occasional funding challenges, and questions about the value of seasonal outlooks that cannot pin down individual storms, the CSU outlooks have been a spectacular success in drawing media, public, and stakeholder attention to hurricane risk. They have also inspired more than a dozen other organizations--including NOAA--to issue similar outlooks. CSU’s June and August outlooks have demonstrated significant skill in predicting overall tropical cyclone activity in the Atlantic, as measured by a blend of six indices. Their April outlooks are less skillful, but in 23 out of 33 years they accurately pegged months ahead of time whether the coming season would see above- or below-average activity. One of Gray’s biggest forecast successes was predicting--as far back as 1990--the onset of a very active era of Atlantic hurricanes that began with a bang in 1995 and which may have now drawn to a close. Gray attributed the 1990s shift to a change in the Atlantic Thermohaline Circulation, a conclusion that remains somewhat controversial, although the shift itself is beyond dispute.

Much of the biographical material above was drawn from the excellent chapter-long portrait of Gray in Chris Mooney’s 2007 book “Storm World.”


Figure 3. Dr. Bill Gray at the podium of the American Meteorological Society’s 27th Conference on Tropical Meteorology, held in April 2006 in Monterey, California. Image credit: Jeff Masters.

Reflections from Dr. Jeff Masters on Bill Gray's career
I had the honor of chatting with Bill Gray a number of times at hurricane conferences, and enjoyed his colorful presentations and tremendous insight on how hurricanes work. His death is a tremendous loss for the hurricane research community, and I feel privileged to have known him. Dr. Gray's expertise was primarily data-based observational science and forecasts using statistical models. He was not a climate change specialist--though he did do some theoretical work related to climate change, attempting to link global temperature trends to the Atlantic Thermohaline Circulation. This work was not highly regarded in the scientific community. Dr. Gray did not accept any climate science done using complex computer-based General Circulation Models (GCMs). His belief that "the last century’s global warming of about 1 degree F is not a consequence of human activities" was prominently featured in the media and on the pages of many climate denier websites.

That aside, Dr. Gray's contributions to hurricane science deserve tremendous appreciation. In addition to his huge number of peer-reviewed scientific papers on hurricanes, he has given the hurricane science community perhaps an even greater gift: a plethora of his Ph.D. students have gone on to become formidable hurricane researchers in their own right. Dr. Gray mentored more than 70 master's and doctoral students at CSU. His final graduate student was Phil Klotzbach, who wrote a moving eulogy that highlighted Dr. Gray’s passion and dedication to atmospheric science:

“Even at the end, Dr. Gray was focused on his research. He gave me very clear instructions on various projects I should be conducting over the next few years. He was still sketching clouds using his legal pad and #2 pencils and discussing the intricacies of cumulus convection when I came to see him a few days before his death. He told me several times throughout my time at CSU: ‘The only immortality that you have as a professor is through your graduate students.’”

Bob Henson and Jeff Masters


Figure 4. Dr. William Gray (second from left) at his CSU office in October 2006 with Jonathan Vigh [left], a CSU student of Dr. Wayne Schubert and now at the National Center for Atmospheric Research, and (second from right) Phil Klotzbach (CSU). At far right is Brian McNoldy (University of Miami/RSMAS), who was a close colleague of Dr. Gray’s during his 14 years at CSU. Image credit: Courtesy Brian McNoldy.