Tornado watch issued for Rochester region

Update: The National Weather Service has issued a tornado watch through 11 p.m. for counties in New York state including Monroe, Ontario, Livingston and Wayne.

A watch means a tornado is possible, versus a warning, which means it's imminent.

The following counties are also included in the watch: Allegany, Broome, Cattaraugus, Cayuga, Chautauqua, Chemung, Chenango, Cortland, Delaware, Erie, Franklin, Genesee, Hamilton, Herkimer, Jefferson, Lewis, Madison, Niagara, Oneida, Onondaga, Orleans, Oswego, Otsego, Schuyler, Seneca, St. Lawrence, Steuben, Sullivan, Tioga, Tompkins, Wyoming and Yates.

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Original story: Dangerous heat and potentially severe thunderstorms are in the forecast for Thursday for western New York, but particularly for the Genesee Valley Region, which includes Monroe, Orleans, Wayne, Genesee, Livingston, Wyoming and Allegany counties.

The National Weather Service in Buffalo already has issued a heat advisory.

The air temperature could reach 91 degrees today, but the heat index — how hot it feels when the air temperature is combined with relative humidity — could hit 100, said meteorologist Dave Zaff.

“It’s going to be pretty miserable this afternoon around, say, 2 to 4 p.m.,” he said.

That misery will be followed by thunderstorms, which could become severe.

Lightning, heavy downpours and wind gusts exceeding 58 mph are all possible.

An isolated tornado isn’t out of the question, although the chances of one developing are pretty low, he said.

The storms will taper off during the evening, after which temperatures will drop, he said.

It should be cooler, less humid and breezy on Friday. And while thunderstorms are also possible Friday, they should not be severe, he said.

New York State Electric & Gas and Rochester Gas and Electric issued a statement saying they are monitoring weather forecasts and have crews and equipment on standby in the event of downed power lines and power outages.

Reporter Marcia Greenwood covers general assignments. Send story tips to [email protected]. Follow her on Twitter @MarciaGreenwood.