“So far this year we’ve had three 90-degree days, and we average at least one 100 degree day almost annually in Denver, so we’re just waiting to see that heat really build,” said Greg Heavener, warning coordination meteorologist with the National Weather Service’s Boulder office. “It doesn’t really look like in the next week or 10 days we’re going to get there.”

Hitting 100 degrees this early in June isn’t unheard of in Denver — the city’s earliest daily record high to hit 100 degrees was June 11, 2022, according to NWS data. But the three all hit 105 degrees later in June in 2012 and 2018.

“Usually we see heat peak in late June and early July,” Heavener said. Humidity from the monsoon season, which typically starts later in July, may keep things a little cooler as the summer progresses, he added.

Denver’s most recent 100-degree day was July 9, the only time the weather hit triple digits at Denver International Airport in 2025,

Unlike lower elevations in Colorado, seeing multiple 100-degree days is relatively rare in Denver, NWS data shows. Even having two can earn a spot on the agency’s list of the in a year.

The top spot belongs to 2012, when Denver recorded 13 days of 100 degrees or hotter. That’s the same year Denver saw a five-day streak of 100-degrees or hotter in late June. Two other heat waves tying the No. 1 spot happened in July 2005 and 1989.

Folks hoping for an early cool-down from the coming El Niño will be disappointed, Heavener said. The weather pattern doesn’t have much of a connection to summer weather in Colorado, and its influence is more pronounced in the fall and winter months.

On the flip side, Denverites who want to bake in the sun even sooner can take a road trip south or west on Wednesday, when forecasters expect temperatures to exceed 100 degrees in , and .

“There is a 63% chance of a very strong El Niño during November (to) January that would rank among the largest El Niño events in the historical record going back to 1950,” according to .

The weather pattern, marked by natural warming of the Pacific Ocean, occurs on average every two to seven years, and typically lasts nine to 12 months.

El Nino is here and scientists fear it’ll be big, bad and costly with heat, floods, droughts, fires

It primarily impacts the Northern Hemisphere in winter, bringing drier weather to the northern parts of the United States and wetter conditions across the southern United States. Colorado falls in the middle of those two regions, but experts say the pattern typically brings wetter weather to the state.

A particularly strong El Niño season can also shift the Pacific jet stream, leading to more winter storms over California and the southern United States, according to NOAA.

"Even very strong El Niño events do not lead to the expected impact everywhere, but stronger events can more significantly tilt the odds in favor of expected outcomes," according to the advisory.

Colorado was experiencing La Niña conditions, which normally brings snow to Colorado’s northern mountains and dry weather to the rest of the state, until April.

This past winter, the state saw one of its lowest snowpacks on record. Earlier this month, Gov. Jared Polis declared a statewide drought emergency. Nearly all of the state is in some form of drought.

A severe thunderstorm watch has been issued for parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma and Texas until 10 PM CDT

— NWS Pueblo (@NWSPueblo)

The National Weather Service said the area could experience frequent lightning strikes and wind gusts up to 75 mph. A watch means that conditions are right for severe storms to form, while a warning indicates that meteorologists have detected a storm in the area.

Counties under the watch include Las Animas, Baca, Prowers, Bent, Otero, Crowley, Kiowa, Cheyenne, Kit Carson and Yuma.

The member of the fire department, who has not been publicly identified, went to a physical black box and pressed a button to manually turn on the sirens, which sounded for a full three-minute cycle shortly after 4 p.m. Monday as storms rolled through Denver during a tornado watch that covered the Front Range and much of the eastern half of the state.

The man had received a report of a tornado on the ground in northeast Denver, but did not verify that with the or the city’s as required by protocol, said Loa Esquilín García, a spokeswoman for the Office of Emergency Management.

“He was trying to do his best to make sure residents were safe and did not verify that notification, that sighting, and activated the sirens,” she said.

Esquilín García declined to identify the fire department member or say who reported the supposed tornado to the man, but noted the report was not from an official source.

Denver Fire Department Deputy Chief Kathleen Vredenburgh said Tuesday that the department received the unconfirmed report of a tornado from . She said five people on shift within the fire department have access to the alarm system.

“We are working now on policy improvements so that doesn’t happen again,” she said.

The city’s emergency sirens can be triggered remotely or turned on at several physical locations in the city, Esquilín García said. Particular teams within the fire department, Denver International Airport and the Office of Emergency Management are authorized and trained to turn on the sirens. She declined to say exactly where the sirens can be activated, citing the need to keep such locations secure.

The city’s emergency sirens are set up to sound automatically if the National Weather Service office in Boulder issues a tornado warning for Denver, Esquilín García said. In such a scenario, the sirens would sound and residents in the danger zone would also receive an alert on their cellphones, she said.

Similarly, if the city were to sound the siren manually for civil unrest or another emergency, officials would also send out an accompanying cell phone alert, she said.

“We send a message to people’s phones saying, ‘Hey, they are sounding, this is what they mean,’ ” Esquilín García said. “Sirens do not sound without a text alert.”

That did not happen Monday. Instead, the member of the fire department manually set off the sirens on his own, which ran for three minutes before shutting down. The system worked like it was supposed to once it was turned on, and there was no technology failure or malfunction, Esquilín García said.

“The city is implementing corrective actions, including a comprehensive review of alerting policies and procedures and enhancements to training and exercises for personnel involved in emergency alerting and warning operations,” she said in a statement.

Monday’s incident was the third time in five months that city officials accidentally sent out a Denver-wide safety alert. In January, residents across the city received a warning about an “active threat” near the University of Denver — an alert that was “broader… than intended,” city officials later said.

Then, in April, an alert about a robbery in the Ruby Hill neighborhood was again pushed out citywide; police said it was “inadvertently sent out further than intended.”

Greg Heavener, a warning coordination meteorologist at the National Weather Service in Boulder, said Tuesday that people who receive weather warnings or hear sirens should take a few moments to verify the alert with official sources before taking shelter.

The concern with false alarms, he said, is that people eventually start to ignore all alerts, even those that warn of real danger.

“I can’t say at what number of false alarms people start tuning them out,” he said. “But we are in the prime-time severe weather season in Colorado. So if people start ignoring alerts now, it could pose a greater life threat to them. We are getting to that peak. Storms, tornadoes, flash floods are going to continue to increase across the region.”

Esquilín García said Tuesday that city residents can trust the Office of Emergency Management, but acknowledged “shortcomings” in the warning system.

“We do still have a long way to go to keep building that trust,” she said. “… There is that work that is constantly happening to get better at alerts and warnings.”

As of Tuesday morning, had been issued by the weather service for parts of Adams, Arapahoe, Bent, Broomfield, Crowley, Douglas, Denver, Elbert, Fremont, Huerfano, Las Animas, Lincoln, Logan, Morgan, Phillips, Pueblo, Sedwick, Washington and Weld counties.

Red flag warnings were also issued for the San Luis Valley, Gunnison Basin, North Fork Valley and San Juan Valley.

Most of the warnings will be in effect from noon to 9 p.m. on Tuesday, according to the weather service. Wind gusts ranging from 35 mph to 50 mph and humidity as low as 6% to 13% will be possible during that time, forecasters said.

“Conditions will be favorable for rapid fire spread in areas that did not receive significant rainfall on Monday,” forecasters wrote in one warning. “Avoid outdoor burning and any activity that may produce a spark and start a wildfire.”

“Fires will catch and spread rapidly and erratically,” forecasters wrote in another.

Denver, which is included in the red flag warnings, will also see near-record temperatures on Tuesday, . Afternoon highs in the city are expected to peak around 93 degrees, just short of Denver’s 95-degree record for June 9, .

“Today will be hot with temperatures reaching the 90s across the plains,” . “Critical fire weather conditions, isolated severe storms, and isolated gusty winds up to 60 mph are all possible.”

Some towns on the Eastern Plains, including Wray and Laird near the Kansas border, are expected to hit 100 degrees on Tuesday, according to a map from the weather service.

This is a developing story and may be updated.

The ground delay is in effect until 8:59 p.m., The FAA had previously instituted a ground stop at the airport, before shifting to a delay around 5:30 p.m. The average delay is roughly 76 minutes.

Six flights have been canceled at DIA and 897 more have been delayed, . More than half of the delayed flights originated in Denver, and 426 more were bound for the city.

The disruptions come as the National Weather Service projected that the metro area, up to Fort Collins and east across the plains, could face severe thunderstorms and hail as large as 3.5 inches. The NWS had also warned that high winds and tornadoes were possible.

By early evening, most of the storm had moved into the eastern part of the state.

Hail roughly 1 inch in size fell in the metro area, said Greg Heavener, an NWS meteorologist. The hailstones grew in size as the storm moved east, he said, and were potentially as large as baseballs. He said NWS had not received any reports of significant damage from the storm or hail but were still monitoring it.

Update 4:35 p.m.: The emergency sirens that echoed around Denver late Monday afternoon were “sounded inadvertently,” according to the city’s Office of Emergency Management.

“There is no threat of destructive weather to Denver at this time,” the department said.

City spokesman Jon Ewing said the emergency management office would release a more detailed statement later Monday.

Update 4:04 p.m.: The National Weather Service issued another severe thunderstorm warning for Parker, Elizabeth and Franktown that is in effect until 4:45 p.m. Monday.

The storm could bring half-dollar-sized hail and winds of up to 60 mph, according to forecasters. A tornado is also possible.

Update 3:57 p.m.: National Weather Service forecasters issued severe thunderstorm warnings for Denver International Airport, Commerce City and Thornton that are in effect until 4:30 p.m. Monday.

The storm could bring half-dollar-sized hail and winds up to 60 mph, according to the . A tornado also is possible.

A separate in effect until 4:15 p.m. for Evergreen, Golden and Kittredge warns of quarter-sized hail and winds up to 60 mph.

Update 3:25 p.m.: National Weather Service forecasters for Castle Pines, Centennial, Denver, Lakewood, Parker and Thornton that are in effect until 4 p.m. Monday.

Quarter-sized hail and 60 mph winds will be possible, warnings.

Update 2:45 p.m.: A tornado watch has been issued for northeastern Colorado and parts of Kansas and Nebraska, according to the National Weather Service.

The warning area covers Colorado’s Interstate 25 corridor from the Wyoming border south to Colorado Springs, which includes the Denver area, as well as the Eastern Plains, according to the weather service.

Tornados, up to softball-sized hail and damaging wind gusts up to 75 mph will be possible until the watch expires at 9 p.m. Monday, forecasters said.

Original story: Large hail may be headed back to Denver on Monday afternoon, according to the National Weather Service.

and hail larger than 2 inches to hit the metro area and north to Fort Collins. The storms are expected to start at around 2 p.m. and intensify as they move into the Eastern Plains throughout the evening, said Abby Pettett, a meteorologist for the National Weather Service in Boulder. For the area east of downtown Denver and along the I-70 corridor, hail is forecast to surpass 3.5 inches in size.

The hail could do “immense damage,” Pettett said. said it had “high confidence” in its forecast and projected that hail could be as large as 4.5 inches further east.

“Right now, the main threat is that large to very large hail,” Pettett continued. “However, there is also potential for very strong winds and also tornadoes.”

To stay safe from falling hail, the weather service recommends staying indoors, closing any shades or blinds, and otherwise staying away from windows. Drivers should stay in their car and pull over if possible while keeping their back to the windows. Motorists should not pull over beneath underpasses.

The forecast comes a week after a hail storm swept through the Denver area, delaying hundreds of flights at Denver International Airport.

“Hot temperatures will continue Sunday and through the week, with afternoon highs in the 90s across the low elevations,” . “Remember to stay hydrated and limit strenuous outdoor activities!”

As of Sunday morning, for Denver included afternoon highs of:

• 93 degrees on Sunday, five degrees short of Denver’s 98-degree record for June 7, .
• 88 degrees on Monday, 10 degrees short of the city’s 98-degree record for June 8.
• 95 degrees on Tuesday, which would tie Denver’s June 9 record.
• 91 degrees on Wednesday, eight degrees short of the 99-degree record for June 10 in Denver.

Thunderstorms will also be possible in the city between 2 p.m. and 5 p.m. on Monday, according to from the National Weather Service.

Severe thunderstorms are forecast for northeastern Colorado on Monday afternoon and evening, . The biggest threats will be hail larger than a golf ball and damaging winds, according to the weather service.

Denver is not included in the , but the Interstate 25 corridor in northern Colorado may be affected, including Fort Collins, according to the weather service. The largest risk looms on the northeastern plains, forecasters said.

High temperatures are expected to reach 90 degrees in the metro area Friday, with expected highs over the weekend in the mid-90s, according to the National Weather Service in Boulder.

Colorado Gov. Jared Polis declares statewide drought emergency

Isolated thunderstorms with gusty winds are possible Friday south of Denver, forecasters said.

NWS advised people to avoid prolonged outdoor exposure or strenuous activities during the heat of the day.

Forecasters issued a severe thunderstorm warning for parts of Douglas and Weld counties until 5 p.m., including , Franktown, southeastern Castle Pines, Castlewood Canyon and north central Weld County.

Both storms are expected to produce quarter-sized hail and winds up to 50 mph, the National Weather Service said in an alert.

“Damage to vehicles is expected. Hail may accumulate on roadways causing hazardous travel,” agency officials said.

People should take shelter indoors and stay away from windows. Heavy rain may cause flooding, and drivers should not drive on flooded roads.

This is a developing story.