March heat dome raises hot car danger, shuts hiking trails and threatens flower blooms across the West

A record-breaking heat dome is baking parts of the Southwest this week, creating dangerous conditions for outdoor recreation and prompting safety experts to warn about the rising risk of children dying in hot cars.

The unseasonable heat has tens of millions of people experiencing temperatures more typical of late spring or early summer.

Kids and Car Safety is urging extreme caution as the heat intensifies. On average, dozens of children die each year in hot cars across the United States. During a heat wave, temperatures inside a vehicle can rise rapidly, becoming life-threatening within minutes.

"Hot car tragedies can happen to anyone," said Amber Rollins, executive director of Kids and Car Safety. "These incidents are not the result of bad parenting. They are the result of human memory failure, a combination of the right circumstances like changes in routine, and dangerous environmental conditions. With temperatures soaring, the risk is significantly higher right now."

The extreme heat is also disrupting travel plans at popular National Park sites across the West, where visitors hoping to beat summer crowds are now facing trail closures and safety warnings.

An extreme heat warning remains in effect for the inner canyon at Grand Canyon National Park in Arizona through Sunday for areas below 4,000 feet.

At Lake Mead National Recreation Area, rangers have closed trails due to the dangerous conditions. Temperatures were forecast to reach 103 degrees Fahrenheit on Friday.

"Conditions are dangerous, with a high risk of heat illness," the National Park Service said. "Respect all closures. If visiting, know that emergency response may be delayed. Carry extra water, avoid midday heat and know your limits. Closures remain in effect until conditions improve."

The early-season heat is also cutting short a rare superbloom at Death Valley National Park in California and causing Lake Manly to shrink.

Temperatures in Death Valley hit 100 F on Tuesday, tying the record for the earliest occurrence of 100 F on record. This was followed by a high of 102 F on Wednesday and 104 F on Thursday.

Flower blooms ahead of schedule during record heat

The heat could also affect wildflower displays, including in Texas, where the spring bloom season is just getting underway.

Experts at the Lady Bird Johnson Wildflower Center in Austin say uneven rainfall and widespread drought are already leading to a mixed season. More than 96% of Texas is experiencing some level of drought, with parts of South Texas in extreme to exceptional drought.

"We may just have to look a little harder for bluebonnets on the side of the road this year in many locales," said Andrea DeLong-Amaya, the center's horticulture educator. "We're hopeful for more spring rain to bring out the later-blooming flowers. Bluebonnets are great, but the show gets even better as the spring season progresses."

Triple digits mark new US record highs for March

Hundreds of high temperature records will be broken by the time this heat dome releases its grip.

Phoenix hit triple digits on Wednesday, marking the earliest 100-degree day on record for the Arizona city since record-keeping began in 1888. Temperatures continued to climb, with a high of 110 F recorded Thursday near Martinez Lake, Arizona - setting a new U.S. high temperature for March.

The triple-digit heat is arriving about a month before Phoenix typically begins issuing weekly heat reports, when Maricopa County also starts tracking heat-related deaths in its seasonal database.

AccuWeather forecasters say the heat will intensify into next week before the heat loosens its grip.