A massive winter storm sweeping across much of the country left more than one million Americans without electricity by Sunday afternoon, placing extreme stress on the nation’s power grid.

By around 10:47 a.m. ET, approximately 850,000 customers were already in the dark, according to Reuters, which cited data from PowerOutage.us. By 2:35 p.m. ET, Tennessee reported the highest number of outages, with about 306,700 customers affected.

Mississippi followed with roughly 175,300 outages, while Louisiana recorded close to 145,100, based on figures from PowerOutage.us.
Additional widespread outages were reported in several other states. Texas saw about 93,000 customers lose service, Georgia had 80,700, Kentucky reported 69,500, West Virginia had 35,500, and Alabama recorded 31,800.

The storm system, which spans more than 2,300 miles, has caused major price swings in electricity markets and forced grid operators in some areas to rely temporarily on oil-fired power plants to keep up with demand, Reuters reported.

PJM Interconnection — the largest regional power grid in the country, serving about 67 million people across the East and Mid-Atlantic — experienced a dramatic spike in wholesale power prices early Saturday. Rates briefly jumped above $3,000 per megawatt-hour, compared with less than $200 earlier that same day, according to Reuters.

In New England, power providers increased fuel oil generation to reduce pressure on natural gas supplies, which serve as the region’s primary energy source, Reuters said.

According to Didi Caldwell, founder and CEO of Global Location Strategies, the current strain highlights the nation’s growing reliance on natural gas delivery systems.

Natural gas now accounts for about 40% of U.S. electricity generation, up from roughly 12% in 1990, making continuous supply essential during extreme weather, Caldwell explained.

“What we lack is sufficient capacity to store and deliver gas in real time,” Caldwell told FOX Business, while noting that the country has ample reserves.

Unlike coal-fired plants, which historically stored months of fuel on-site, most natural gas facilities depend on just-in-time delivery. Any interruption to pipelines or infrastructure can rapidly jeopardize electricity production, Caldwell said.

“If anything happens to disrupt the supply of gas to the generating stations, they have little to no practical backup,” she said.

Cold weather further intensifies the risk, as households increase heating usage at the same time electricity demand rises — much of it powered by natural gas.

“Every region is exposed, but for different reasons,” Caldwell said. “In the southeast, the lack of storage and limited transport capacity means that, during cold snaps, natural gas is competing with itself.”