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Spatial analysis suggest hail "hot spots" for cloud seeding experiments in Colorado


The lee side of the Rocky Mountains experiences the most frequent, intense and severe

hailstorms, but more specifically, the state of Colorado (Mahoney et al., 2012). Cloud seeding seeks to engineer clouds in order to decrease hail size for various benefits such as for the agricultural industry. Fully-funded and operational cloud seeding programs have been on-going in the USA since the1950’s, although literature shows controversial results (Strong et al., 2007). While the loss of crops is costly, cloud seeding also has a large price tag. Where weather engineering is used to decrease hail size and frequency, it is critical to ensure operations occur where the benefit is most needed. This brief research attempts to highlight the possible areas where cloud seeding could be the most beneficial in the state of Colorado.

Figure 2: Colorado state depicted location across contiguous United States. Map by Larissa Gospodyn 2019.

Publicly available data were obtained from the Colorado Department of Agriculture, USGS, ESRI, NCDC (NWS), SPC and NOAA from April to September from 1988-2017. This 6-month interval over the 30 years was chosen to represent an approximate growing season, where crops would be most impacted. ESRI’s ArcGIS software was used to analyze and visualize the results, as shown below.

Figure 3: Baseball-size hail June 4th 2015 in Simla, Colorado


An Optimized Hot Spot Analysis was used to generate hot spots where clusters of large hail size (magnitude) were reported in Figure 4. This doesn’t mean large hail wasn’t reported anywhere else, but this shows locations within close proximity of other locations where large hail was reported. Darkest red shows highest significance of large hail whereas darkest blue shows lowest significance. Grey dots show all hail reports.

Figure 4: Darkest red shows highest significance of large hail whereas darkest blue shows lowest significance. Grey dots show all hail reports. Map produced by Larissa Gospodyn 2019.


When examining the spatial variability of the data (Figure 4), it is clear that the northeast region of Colorado experiences the largest hail size (magnitude). It is also apparent that an overwhelming majority of hail reports are collected roadside, which poses a limitation to the analysis in the true distribution of large hail across an agricultural area potentially dominated by fields (i.e. no roadways).

Figure 5: Hot spot analysis and total agricultural sales from 2012 to present. Map produced by Larissa Gospodyn 2019.

Results from the hot spot analysis and total annual agriculture sales per county in 2012 were overlaid in Figure 5. Where the goal of cloud seeding is to protect the agricultural sector or minimize insurance claims due to hail damage, cloud-seeding operations in Colorado may have the largest impact in Morgan County (circled in pink).

Author: Larissa Gospodyn

Editor: Francis Lavigne-Theriault


Mahoney, K., Alexander, M.A., Thompson, G., Barsugli, J.J. & Scott, J.D. (2012). Changes in hail and flood risk in high-resolution simulations over Colorado’s mountains. Nature Climate Change, 2, 125-131.

Strong, G.S., Kochtubajda, B., Summers, P.W., Renick, J.H., Krauss, T.W., Humphries, R.G. & Lozowski, E.P. (2007). 50th Anniversary of hail studies in Alberta: Accomplishments and legacy. CMOS Bulletin SCMO Special Issue, 35, 3-19.

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Worked for the North Dakota Weather Modification Board back in the late 1970's as a meteorologist guiding seed planes along and around t-storms in western North Dakota. I am convinced we made a difference in hail reduction with the storms although rainfall enhancement wasn't quite as noticable. The only negative part we saw about the hail suppression was we occasionally ended up with more heavy rains in the areas seeded for hail resulting in field flooding. We did most of the seeding using iodine generators and flares mounted on twin engine cessnas. It was an interesting job.

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