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A thick layer of hail covers the lawn as a motorist guides a Toyota RAV-4 through a flooded intersection after a storm packing heavy rains and hail hit Monday, May 14, 2018, in southeast Denver. Photo by David Zalubowski / AP Photo

What Do Colorado’s Severe Weather Events from the Last 12 Years Tell Us?

The National Weather Service's data on Colorado's flash floods, severe thunderstorms, and tornadoes don't reveal many clear trends, but the reports do highlight the vast fluctuations in our weather system.

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Colorado residents have one thing in common—we are all exposed to a great variety of weather conditions, and in some cases, these events can be life-threatening and extremely damaging.

Some years in Colorado are pretty lackluster in regard to severe storm reports. Other years, Colorado tops the charts. If you’ve lived here for awhile, you can likely remember certain hail storms, flash floods, and tornadoes, but unless you’re constantly geeking out about the weather, most severe storm reports probably fly under the radar for you. Pun intended.

Thousands of storm reports have been submitted to the National Weather Service over the past decade-plus, and thankfully, they archive them all. Recently, the NWS in Boulder released some interesting data about the last 12 years of severe weather events. While the below charts show minor trends, if we want to gather a more precise and accurate report, we would want to look at data from the last 30–50 years (or more). Still, it is fascinating to look back on the weather events that have made news over the years, and marvel at the vast fluctuations in Colorado’s weather system.

Flash Flood Reports

Courtesy of the National Weather Service

Flash flooding is a weather phenomenon that you may not associate much with Colorado, since most of the population lives in a semi-arid climate. But when we do get a flash-flood event, it’s typically a very big deal. In the last 12 years, there have been 197 reports of flash flooding. From 2016–19, there were 16 flash-flood reports, while during the four years prior to that, 2012–15, there were 127 reports.

What stands out the most when looking at the NWS’s flash-flood data is that there were 76 events in 2013. Most Coloradans remember the 2013 floods, which occurred September 11–17, devastated over a dozen Front Range cities, and left nine people dead. From this data, we can see an apparent lack of flash flood events in the last four years, but that followed a rather active flash flood cycle from 2008 to 2015, so there is no real trend that we can gather from this data.

Severe Thunderstorm Reports

Courtesy of the National Weather Service

Being from Colorado, you almost certainly know what a severe thunderstorm is composed of—very heavy rain, large hail, and strong winds. But what actually makes a storm severe is winds greater than 58 mph and hail larger than an inch in diameter.

When we look back over the last 12 years of data on severe thunderstorms, you’ll immediately notice that 2018 and 2019 have had the most hail reports out of any of the 12 years referenced. If you look at all the years together, you’ll notice some ups and downs, which makes it tough to spot trends. But take a look at 2017. You may remember May 8, 2017—the day Denver received golf ball to grapefruit-sized hail around the metro area the led to $1.4 billion in damage. 2017 was overall a very mediocre year in terms of thunderstorm reports, but one big event changed it into a historic year.

On the other hand, our wind reports over the last 12 years are rather consistent—with 25 to 50 reports of damaging winds coming through every year.

Tornado Reports

Courtesy of the National Weather Service

We are no strangers to tornadoes here in Colorado, especially on the Eastern Plains, which is technically in tornado alley. Tornadoes are ranked on the Enhanced Fujita (EF) scale, with EF-0 being the weakest, and EF-5 being the strongest. Colorado sees more EF-0 rated tornadoes—those with winds between 65-86 mph—than other ratings, but over the last 12 years we’ve also seen three that were rated EF-3. One of the strongest tornadoes in the last 12 years happened in Boulder County on June 2, 2015. An EF-3 tornado with maximum winds of 135 to 140 mph was on the ground for 6 miles from areas just south of Berthoud to areas to the west/northwest which is a rare direction for tornadoes in Colorado to move. Overall there are not many trends to be spotted in this data either, but it seems as though we have a two to three active years, followed by a couple of calm years.

Overall, Colorado’s severe weather season is dependent on plenty of atmospheric variables that makes it difficult to predict. But this data is beneficial when comparing weather patterns to those in the past. All we can is be aware of the wide array of weather we get here in Colorado, be prepared for the extremes, and try to think of ourselves as lucky to be able to experience Mother Nature’s power all while enjoy the 300 days of sunshine Colorado is known for.

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