According to the NWS, an Excessive Heat Warning is issued within 12 hours of the onset of "extremely dangerous heat conditions." It will be lifted late Monday and changed to "Heat Advisory" issued.

The heat wave enveloping the eastern and central U.S. through the holiday isn't missing upstate New York.

The National Weather Service issued a "Heat Advisory" for Saturday, June 30, and late Monday, July 2 — and a more urgent "Excessive Heat Warning" for Sunday, July 1, and much of Monday — for much of west and central New York, including Ontario, Monroe, Yates and Livingston counties.

According to the NWS, an Excessive Heat Warning is issued within 12 hours of the onset of "extremely dangerous heat conditions." These warnings generally are issued when the maximum heat index temperature is expected to be 105 degrees or higher for at least two days and night air temperatures will not drop below 75 degrees. The NWS warns: "If you don't take precautions immediately when conditions are extreme, you may become seriously ill or even die."

Heat Advisories, such as those issued for Saturday, are also issued within 12 hours of the onset of extremely dangerous heat conditions, but with the maximum heat index temperature expected to be 100 or higher. The same warning about taking precautions applies. Particularly at risk are elderly and very young people, pregnant women, and people with heart and/or respiratory conditions who don't have air conditioning.

The Excessive Heat Warning is in effect from noon Sunday through late Monday evening. The highest heat index values will be from noon through 8 p.m. each day — possibly reaching as high as 105 to 110 Sunday and Monday. 

Precautions to take include the following, says the NWS:

• Drink plenty of fluids, particularly water.

• Stay out of the sun as far as possible. Try to reschedule any strenuous outdoor activities to early morning or evening.

• If working outdoors, schedule frequent rest breaks in shaded or air-conditioned environments.

• Do not leave young children or pets unattended in vehicles under any circumstances, particularly in extreme weather conditions.