Hot weather, a growing economy and the early retirement of coal-fired plants could mean a heightened risk of blackouts this summer, according to the nation’s electric grid watchdog.

The North American Electric Reliability Corporation (NERC) has warned that parts of the upper Midwest face a “high risk” of energy emergencies under certain conditions, such as extreme heat or unexpected generator outages.

“It’s a sobering report,” said John Moura, NERC’s director of reliability assessment and performance analysis. Last month, the Midwest grid operator — the Midcontinent Independent System Operator, or MISO — warned that generation capacity in the region including Minnesota and Wisconsin will be about 1,230 megawatts short of possible peak demand. With above-average temperatures forecast, MISO said it may need to rely on imports or emergency measures to maintain the grid.