Power plant outages surged along the eastern United States on Sunday as constricted natural gas supplies and frigid temperatures cut the electricity output of the region's generation fleet.

The PJM Interconnection, the largest U.S. regional grid that serves 67 million people in the East and Mid-Atlantic, reported nearly 21 gigawatts of generation outages, with most of that capacity being forced offline. Those outages represented about 16 percent of PJM's Sunday afternoon demand of 127.4 GW.

On Sunday afternoon, PJM issued a pre-emergency order mandating that some customers in its curtailment program curb their electricity use. Customers in the program get paid to curb their electricity during critical periods.

Without native supplies of natural gas, the Eastern seaboard relies on a pipeline network that is historically constricted during extended bouts of frigid weather, said Pieter Mul, a grid expert and associate partner at PA Consulting's energy and utilities practice.

As snow and sleet hit the major cities of Boston, New York, Philadelphia and Washington, DC, the power grid also lost access to solar power in the afternoon from an increase in cloud cover.

Meanwhile, power prices in PJM and the electric grids for New York and New England surged between $400 and $700 per MWh Sunday afternoon, grid operators reported. The increases reflected demand that continues to top grid operator forecasts.

ISO New England, which serves a six-state region that includes Boston and Hartford, reported about 20.2 gigawatts of demand at 1:45 p.m. EDT, or greater than a projected peak load of 19.5 GW expected later in the day.

With constricted natural gas access, nearly 40 percent of the New England grid's output came from oil-fired power plants. Natural gas, usually the grid's main source of fuel, accounted for just 30 percent of the grid's fuel source for power plants.

But as Mul noted, New England supply of diesel fuel oil can be depleted and not easily resupplied during hazardous winter conditions. ISO New England's surplus capacity dropped to about 1.1 GW, down from earlier estimates of several gigawatts.

Outside of Washington D.C., real-time wholesale electricity prices topped $1,800 per MWh early Sunday in Dominion Energy's Virginia territory, up from $200 per MWh on Saturday morning. Virginia houses the biggest cluster of data centers in the world, which are used to power things like artificial intelligence and have been responsible for rising power demand and prices in swaths of the country.

The demand spike began late Saturday night, according to data from PJM as Winter Storm Fern swept across parts of the country.

PJM predicts an all-time winter demand record on Tuesday, partly due to data center electricity needs. Dominion has said extended frigid temperatures this week, along with heavy snow, have the potential to be one of the largest winter events to affect the utility's operations.

Spot wholesale electricity prices across the U.S. have been elevated throughout the weekend as regional grids strain to meet surging demand. When demand is higher than the forecasts, utilities can be forced to pay elevated spot prices for electricity to meet the demands of their residential and business customers.

Regional grids feed their power into the local distribution lines that bring electricity to homes and businesses. Those local power lines are showing disruptions, with nearly 1 million customers without power on Sunday, according to PowerOutage.us, with more than 300,000 in Tennessee and more than 100,000 each in Mississippi, Texas and Louisiana. Other states affected included Kentucky, Georgia, Virginia and Alabama.