Triple-digit heat has singed Houston earlier than at any other time in a decade, straining the power grid serving the fourth-largest U.S. city in what may be a premonition of an unusually hot summer.Temperature readings at Houston’s Hobby International Airport touched 100 degrees Fahrenheit (38 Celsius) on June 13, the earliest that mark has been reached since June 5, 2011, said Cameron Batiste, a National Weather Service meteorologist. The only time that’s happened earlier than 2011 was in 1998 — and both of those summers inspire shudders in long-time Houstonians who recall them as especially brutal seasons.

“This is very early for this kind of heat,” wrote Matt Lanza, a meteorologist with Space City Weather. “Hopefully not a harbinger of things to come this summer… It has felt like August lately.”

Houston was expected to top out at 98 on Tuesday and daily highs were forecast to remain above the 90-degree mark at least into next week, according to the weather service.

The heat is taxing Texas’s power grid just four months after a deadly historic freeze blacked out millions of homes and paralyzed the state for the better part of a week. Right now, the heat has arrived at a time when 12.2 gigawatts of power generation capacity is turned off so crews can do repairs and other maintenance work.

Residents are being asked to turn off appliances and take other conservation measures, a step that in the past has sometimes been a prelude to a full-blown emergency declaration and rolling blackouts. In fact, across the entire U.S. West and the Rocky Mountains extreme heat has been baking cities and farms.

Billings, Montana, is expected to reach 106 on Tuesday, two degrees shy of the all-time high, according to the Weather Service. “It is a little early and a little intense for this time of year,” said Tom Humphrey, a Weather Service meteorologist.