The first official day of summer here, and it means business. With highs in the upper 90s forecasted from Minnesota to Pennsylvania, a lot more people will be blasting fans and air conditioning - and putting a strain on power grids across the nation.

Con Edison, which provides power to most of New York City, recommends that people set their thermostats no lower than 78 degrees and making sure air conditioner filters are clean, so they run efficiently. The company also recommends turning off unused lights, and running large appliances like ovens, washing machines and dishwashers at off-peak hours late at night or early in the morning.

These precautions should protect against overheated power customers from overwhelming the grid, but ConEd spokesman Michael Clendenin says the company will still be keeping a watchful eye on its equipment, which will be heating up both from the sun and increased demand.

Our engineers monitor the system during the heat waves, and if we start to see equipment problems in one neighborhood, we might implement voltage reduction to keep the power flowing, Clendenin says.

Voltage reduction, also known as a brownout, sometimes manifests when lights dim or appliances run a little less smoothly than normal. But often customers won't even notice the difference, according to Clendenin.

A spokesperson for PJM, the country's biggest power grid, told Reuters that he did not anticipate outages.

We expect to have sufficient power supplies and the reserves are covered for the day, Ray Dotter said.