It didn’t look like it was going to storm for most of the day on Wednesday. Then, around 6 p.m., the skies opened up, unleashing a downpour and a burst of hail that most hadn’t seen for some time.
Initially, as Denver’s storm first developed around 6 p.m. on Wednesday afternoon, large quarter-sized hail pelted parts of downtown. But the greatest impact for most turned out to be an epic downpour, just as Wednesday’s rush hour was coming to a close.
#Developing: Flash flood warning issued for metro-Denver. This is street flooding right now at 17th & Humboldt in Uptown. #cowx @DenverChannel @MikeNelson247 pic.twitter.com/cRJ441MhMt
— Russell Haythorn (@RussellHaythorn) August 22, 2019
View from the office of Broadway! pic.twitter.com/SJnuPdd5pS
— Jena Griswold (@JenaGriswold) August 22, 2019
Most of Denver picked up somewhere between three-quarters and an inch and a half of rainfall, but two things stood out about Wednesday’s storm: one, some of the storm’s heaviest rainfall took place in the heart of the city.
Most significantly, though, almost all of the rain came in about an hour, overwhelming drainage systems and inundating streets.
Here's a quick look at how much rain we've received so far, courtesy of @udfcdfws. Rain is slowly decreasing, but Flash Flood Warning remains in effect for much of Denver. Turn around, don't drown. #COwx pic.twitter.com/ogl1CSQNu7
— NWS Boulder (@NWSBoulder) August 22, 2019
The highest rainfall total from the Colorado Department of Transportation’s Urban Drainage and Flood Control District’s network of stations was a 1.89 inch amount at a station on 3rd Avenue and Speer Boulevard. That rainfall fell entirely in a 75-minute span between 6:15 p.m. and 7:30 p.m. on Wednesday evening.
For context, Denver averages less than two inches of rain in the entire month of August. So, a 1.89″ rain total in barely over an hour is an unusually high amount of rainfall for the metro area.
1.89” of rain at Speer/3rd Avenue in 75 minutes. Pretty bonkers.#COwx pic.twitter.com/mZTjhtHoa3
— Chris Bianchi (@BianchiWeather) August 22, 2019
Many of the ingredients typically needed for severe weather along the Front Range were quite clearly in place early in the day on Wednesday. Dew points near 60 degrees – a bit of a magic number for the Denver area – were in place on Wednesday afternoon. Relatively high values of wind shear would allow storms to grow and sustain themselves for a prolonged period of time.
As a result, the Storm Prediction Center (SPC), the governing body for severe weather, issued a Severe Thunderstorm Watch for Denver and the entire metro area early on Wednesday afternoon.
Then, as the storms first developed, a so-called Denver Convergence Vorticity Zone – basically, a natural area of spin due to Denver’s geography – helped draw in extra moisture from the east to further fuel the storms. That extra push of moisture helped these storms re-develop, and it concentrated some of the heaviest of the rainfall over the heart of Denver.
DCVZ ingesting moisture and back-building this mess.
Translation: flooding a real threat/concern. If you don’t have to travel now, please don’t. pic.twitter.com/ZBfXkEoJeh
— Chris Bianchi (@BianchiWeather) August 22, 2019
The result? A messy commute for many, and a storm that Denver hadn’t seen for quite some time.
