The Bomb Cyclone: Lowest Pressure Ever Recorded in Colorado
Thinking back to March 2019 probably makes you shiver just a bit; that was the month that not one, but two bomb cyclones hit the state. The term "bomb cyclone" references a dramatic change in intensity of a storm in a 24-hour period; the most notable stat came from Lamar on March 13, when the weather-reporting station there recorded a sea-level pressure of 970.4 mb (millibars), breaking the old record of 975.0 mb also set at Lamar for the lowest sea-level pressure ever recorded in the state. To put that into perspective, a surface pressure of 970.4 mb is typically found in a Category 2 hurricane. Denver International Airport also broke its sea-level pressure record that day, with a pressure reading of 979.01 mb. During the storm, Colorado Springs reported gusts of up to 96 mph and Denver International Airport of 80 mph, breaking all-time non-thunderstorm wind records.
Severe storms are nothing new here in Colorado, nor is hail. But one particularly severe thunderstorm produced the largest hailstone ever recorded in the state. On Tuesday, August 13, the Colorado Climate Center and the National Weather Service measured a hailstone that had fallen northwest of Bethune. The maximum diameter was 4.83", which exceeded the longstanding state record of 4.5". To put it into perspective, a softball measures 3.5” in diameter; the Bethune hailstone was 22 percent larger.
State’s Highest Temperature Ever
In another wild weather swing, Colorado went from a record snowpack in June to the hottest temperature ever recorded in the state a month later. On July 20, a weather station near the John Martin Dam in Bent County reported a temperature of 115 degrees Fahrenheit, officially the highest temperature ever recorded in Colorado, beating the previous record of 114 degrees set in 1933 and matched in 1954. The Colorado Climate Center and the National Weather Service went through a vicious verification process to confirm that the thermometer correctly reported this new mark.
Extreme “Black” Danger Level
March saw an unprecedented number of powerful avalanches in Colorado, after between two and a half and seven feet of snow dumped on most mountain areas at the start of the month. The Colorado Avalanche Center recorded nearly 1,000 avalanches in the first two weeks of March, but it's suspected that the real number was closer to 5,000. Avalanches are ranked on a scale of D1 to D5, with D5 the strongest; the CAC documented 87 avalanches at or above D4. March 7 became known in Summit County as “Black Thursday,” as four back-country zones went to extreme “black” danger levels. In other areas of the state, a handful of mega slides registered D5 on the United States Avalanche Rating Code, which defines a D5 as a slide so strong it can “gouge” the landscape, and that’s exactly what happened. Drive through the Colorado high country in the summer, and you can see the scars of those avalanches.
Warmest September on Record
Summer heat in Colorado is no joke. With numerous 90-degree days and several 100-degree days occurring on a normal basis, we’re used to the heat. But September 2019 was more of a scorcher than any other September since Colorado began keeping records in 1895. The average temperature in Denver during those thirty days was 69.3 degrees Fahrenheit, almost 6 degrees above our normal September temperature.
Drought-Free for the First Time Ever
The U.S. Drought Monitor was established back in 2000; since then, there has always been at least a part of this state impacted by drought. Until this year, that is. From May 21 through July 16, there was no reported drought anywhere in the state, thanks to a wet spring after an active winter. That streak ended on July 23, when dry conditions returned.
July Mountain Snowpack
Because of that active winter and an extremely snowy spring, there were some crazy snowpack percentages reported, upwards of 500 to 10,000 percent of normal. Only three other years beat 2019 in terms of snowpack for the Upper Colorado River Basin. The amount of snow that lingered into the summer months inspired Arapahoe Basin Ski Area to stay open until the Fourth of July, and led to amazing but dangerous whitewater rafting experiences across the state.
November regularly ranks as Colorado's fifth snowiest month out of the ten in which we typically see at least a trace of snow in Denver. But this November blew past the average November snowfall of 7.5 inches, almost doubling it in just one storm. A blizzard that hit three days before Thanksgiving produced 8 to 22 inches of snow along the Front Range, and 15 to 40 inches of snow in the foothills. Some Denver streets are still wearing the signs of the storm.
Summer Solstice Snowstorm
June is typically a month when Colorado sees very little snowfall, even in higher terrain. But on the summer solstice, the central and north-central mountains in this state experienced a rare snowstorm that dropped up to two feet of snow on areas above 9,000 feet, increasing the snowpack as the state headed into the warmer months.
Fourth of July Severe Weather
On Independence Day, Coloradans were enjoying the great outdoors when all of a sudden great hailstones started falling. From July 4 to 5, there were sixty reports of significant hail across the Front Range. Many of those reports came from Denver County, where golf ball-sized hail landed. Holyoke reported a tornado, but it did less damage than that hail.