Denverites need to watch out for the cloud Thursday. 

No, not the brown cloud that the city’s pollution brings — but rather the “green” cloud that will be over Civic Center Park during Denver’s Mile High 420 Festival presented by Jars Cannabis. It goes from 1 to 10 p.m. Thursday. 

With more than 37,000 participants descending on downtown, expect traffic delays and little available parking in the whole Civic Center Park area.

“The event is permitted for Bannock Street from 14th Avenue to Colfax Avenue (this stretch is already permanently closed to vehicle through-travel),” said Nancy Kuhn, spokesperson for the city’s Department of Transportation and Infrastructure. “They’ll be utilizing 14th Avenue from Cherokee to Broadway. The permit for the street closures is already in place for event setup.”

New for 2023: No minors allowed. Participants must be 21 years or older.

“We just want to do the responsible thing,” said Ashley Chuban, Jars Colorado correspondent and FlyHi chief operating officer. “We’re creating a great community culture and priortizing safety — that’s our number one  goal is for everyone to be safe and have fun.”

Concerns raised last year by a non-profit advocacy group that “focuses on protecting kids across the nation from the dangers of today’s marijuana” prompted the Festival organizers to commit to restricting entry to adults, according to a news release from One Chance to Grow Up. 

But Chuban said “we’ve always wanted to be a 21+ event.”

“We’d like to express our gratitude to the One Chance to Grow Up group for helping us spread the word that this is an adult event,” she said. “We’re an adult business.” 

The festival includes music from Rick Ross, Fivio Foreign, Waka Flocka Flame and others. It’s hosted by Tommy Chong — half of the former comedy duo Cheech & Chong. There’s also food booths, a beer garden and vendor booths. 

While the event is free, tickets will still be required to get in the gates. 

And as far as that cloud is concerned, organizers would like to remind attendees open weed smoking is illegal in Colorado (no winks — really). 

“Public consumption of marijuana is prohibited under Colorado State law,” according to the festival’s website. “It is also illegal to possess more than one ounce of marijuana or its equivalent in marijuana products under Colorado State law. Anyone caught distributing marijuana or using any illegal substances at the event may be removed from the event by local authorities.”

But to avoid potential contact high — based on previous festivals — residents and visitors might want to avoid the area come long about 4:20 p.m. Thursday.

One Chance to Grow Up is a self described grassroots organization dedicated to “defending kids from the dangers of marijuana.”

Colorado law prohibits the sale of recreational marijuana to those under the age of 21. Despite this, One Chance to Grow Up said Denver Public Schools attendance dips when the festival falls on a school day. 

“This (age) policy reinforces both the law and a growing body of public health research: Marijuana use is harmful to young people whose brains are still growing,” Alton Dillard, a spokesperson for One Chance to Grow Up, said in a news release. “We are glad that the event organizers and the city agree that attendance should include only those who can legally consume recreational marijuana.” 

Wednesday, the Colorado Department of Transportation (CDOT) hosted an hours long workshop to demonstrate what a cannabis impairment looks like. Volunteers consumed cannabis in a controlled environment and submitted to testing by law enforcement. 

Research does show cannabis and the associated industry has a significant and positive influence on customers, CDOT said. However, as consumption rises, so too have deadly accidents.

“As of 2022, more than one-third of all fatalities in Colorado roads involve an impaired driver,” CDOT said in a news release. “Deaths involving a driver who tested above the legal limit for active THC increased 58% between 2020 and 2021.” 

Since 2019, deaths on Colorado roads involving a driver impaired by alcohol, drugs or a combination of the two increased by almost 60%, according to CDOT. 

The CDOT workshop was held in partnership with Responsibility.org, the Marijuana Industry Group, Canopy Growth, Wana, the Colorado Bureau of Investigation and Intoximeters. 

“There are a lot of misconceptions out there when it comes to cannabis-impaired driving,” said Glenn Davis of CDOT’s Highway Safety Office in a release. “Our goal is to give folks in the industry the knowledge and tools to keep their patrons safe by steering them away from risky behaviors like driving high.”

Denver Gazette city editor Dennis Huspeni contributed to this story.