LOS ANGELES (NewsNation Now) — An unusually early and long-lasting heat wave is bringing more triple-digit temperatures to a large swath of the U.S. West, raising concerns that such extreme weather could become the new normal amid a decades-long drought.

The dome of high pressure spread over the West the week before the official start of summer, causing unusually hot days and warm evenings.

In California, the operator of the state’s power grid is asking residents to voluntarily conserve power for a few hours Thursday evening as record-breaking heat blankets the West this week.

The California Independent System Operator issued the flex alert to help relieve stress on the grid. It asks people to set thermostats to 78 degrees or higher, turn off unnecessary lights and avoid using major appliances. CEO Elliot Mainzer said the grid was stable and there was no expectation of rotating power outages, but that could change as temperatures spike in the coming days.

Higher temperatures also were felt in the normally temperate San Francisco Bay Area. A few cooling centers were open but mostly empty by the afternoon.

Kathleen Craft, shelter coordinator for the city of Livermore, California, said temperatures had reached 99 degrees shortly after midday but only one woman had shown up at the city’s cooling center.

Wildfires out West

Elsewhere in the West, triple-digit heat was forecast in Denver, which saw a record high of 101 degrees Tuesday. The weather service issued an excessive heat warning for parts of western Colorado, most of which is experiencing extreme drought conditions.

In Montana, wildfires have exploded in size, triggering evacuations and destroying an unknown number of homes as furious winds stoked the blazes and caused a firefighting helicopter to crash-land, officials said .

The sudden ramping up of the fire season came as record-high, triple-digit temperatures early in the week baked much of Montana and portions of northern Wyoming. At least 14 new fires were reported in the two states since Tuesday.

A state Department of Natural Resources and Conservation fire helicopter crash-landed in the heavy winds, rolled over and caught fire. The five people aboard got out safely and were taken to hospitals for minor injuries before being released Tuesday night, agency spokesperson Paige Cohn said. The crash remains under review, she said.

A subdivision with 65 houses and cabins was evacuated as the flames neared. Aircraft dropped retardant Wednesday to slow the fire’s advance on the Grassy Mountain subdivision.