Hurricane Laura’s lashing of south Louisiana and southeast Texas on Thursday led MISO to implement last-resort rolling power outages in an Entergy load pocket during restoration efforts.

MISO said its southern member companies are reporting widespread destruction following the storm. Citing transmission system damage and generation outages, MISO directed Entergy to begin periodic power outages just before noon ET in the Atchafalaya Basin load pocket straddling Texas and Louisiana.

It’s unclear how many customers were affected. MISO also cited Laura’s “unpredictable load patterns” as another reason for the load shedding. Entergy was asked to report its load-shed activities through the nonpublic MISO Communications System.

“MISO has implemented emergency operating procedures to address reliability in a load pocket of the region that experienced significant damage from the hurricane,” System Operations Executive Director Renuka Chatterjee said in a statement. “While we continue to support our members’ restoration efforts in the South Region, we maintain our focus on ensuring grid reliability across the entire footprint.”

The RTO said it “escalated to the most severe step in its emergency actions in order to avoid a larger power outage on the bulk electric system in the affected areas.” Periodic load shedding to stymie a more severe blackout was in effect for about 12 hours; the maximum generation emergency was lifted around 10:55 p.m. ET.

MISO has never shed firm load because of a capacity emergency since it began running its market in the new millennium, though it has shed local load during transmission outages. This appears to be the first time that MISO has shed load because of a capacity shortfall and transmission outages. The grid operator called it a “highly unusual action.”

During the blackouts, energy was priced at MISO’s $3,500/MWh value of lost load. The grid operator has been in discussions with its stakeholders to raise the current price limit, saying it could be undervaluing involuntary load sheds. (See MISO Revisits Scarcity Pricing Rethink.)

Entergy appealed to its Texas customers that they pare down their electricity usage.

“The unusual circumstance is the result of extensive damage to Entergy’s transmission system caused by Hurricane Laura in east Texas and west Louisiana and the anticipated high demand for electricity due to high temperatures. Hurricane Laura damaged conductors [and] wooden and steel towers in key transmission lines needed to bring electrical power from the east,” the utility said.

Entergy on Thursday reported more than 540,000 customers without power in its service territory. The utility said it convened a 16,750-strong restoration crew, more than double what it originally pledged before the storm. By Monday, the utility said it restored power to about 115,000 Louisiana customers.

In the height of the storm’s wake, nearly 1 million total customers were without power, according to the Edison Electric Institute. Restoration crews were able to half that number over the weekend, with more than 29,000 workers from at least 29 states, D.C. and Canada assisting the region in restoration efforts, the nonprofit reported.

Entergy said its hardest-hit areas are the Lake Charles, Calcasieu and Cameron parishes, which collectively account for 5,648 poles in need of repairs, 10,037 spans of inoperable wire and 2,484 mangled transformers.

While MISO as a rule doesn’t reveal what member assets are offline from outages, Montgomery County, Texas, County Judge Mark Keough said on Facebook late Thursday that Entergy Texas successfully re-energized its 500-kV Hartburg line.

“Please watch energy consumption for the next few days to ensure we are not putting pressure on the grid as they have to balance the load,” Keough said in his post.

Keough also said Entergy was restoring power to a generator on Thursday and continued to make transmission repairs. He said Entergy was “confident” that its restoration work will avoid the need for further load shed.

MISO extended by a day on Thursday a conservative operations declaration issued ahead of the storm. (See Gulf Grid Operators, Utilities Shore up for Laura.) The RTO also said additional declarations and alerts may be issued in the aftermath.

Compounding matters, MISO said it also experienced “challenging capacity availability” in its North and Central regions Thursday because of a heat wave. The bleak capacity picture led the RTO to issue a hot-weather alert for the two regions while control room operators contended with a ravaged MISO South.

“We continue to work with our member companies and partner RTOs like SPP and ERCOT toward a speedy recovery,” South Region Executive Director Daryl Brown said. “Mutual assistance and collaboration before and during the storm as well as throughout restoration are necessary to maintain our focus during times of crisis.”