A National Weather Service heat warning has been extended for western Pennsylvania through Saturday. The warning for Allegheny, Butler, Beaver, Washington, Westmoreland and Fayette counties is now in effect until 8 p.m. June 22. Saturday will be the hottest day of the heat dome, with highs in the 90s. Highs will again reach 100 degrees. Most of the region will remain dry, with only a few isolated storms possible during the heat of the day. More: See current weather warnings for your county. Interactive radar: Track storms in your area. Learn how to turn on automatic weather alerts in the WTAE app. There is also a heat warning for Mercer, Venango, Lawrence, Armstrong, Greene and Indiana counties, as well as the Westmoreland and Fayette Ridges. You can read the full text of the warning and advisory below.EXCESSIVE HEAT WARNING… Dangerously hot conditions with heat index values ​​up to 99.WHERE… Beaver, Fayette, Washington, Allegheny, Butler and Westmoreland Counties.WHEN… Through 8 p.m. EDT Saturday.EFFECTS… Heat-related illnesses increase significantly during extreme heat and high humidity.InstructionsDrink plenty of fluids, stay in an air-conditioned room, avoid the sun, and check on relatives and neighbors.Do not leave small children and pets unattended in vehicles. Car interiors reach lethal temperatures in a matter of minutes.Take extra precautions outdoors. Wear light and loose-fitting clothing. Try to limit strenuous activities to early morning or evening. Take action if you notice symptoms of heat exhaustion and heat stroke. Stay cool, stay hydrated, and stay informed. HEAT ALERTWHAT… Heat index values ​​as high as 97.WHERE… Parts of east-central Ohio, northwest, southwest and western Pennsylvania, and northern and northern panhandle of West Virginia.WHEN… Through 8 p.m. EDT Saturday.EFFECTS… High temperatures and high humidity can cause heat illness.InstructionsDrink plenty of fluids, stay in an air-conditioned space, avoid the sun, and check on relatives and neighbors.Take extra precautions when outdoors. Wear light and loose-fitting clothing. Try to limit strenuous activities to early morning or evening. Act if you notice symptoms of heat exhaustion and heat stroke.To reduce the risk when working outdoors, the Occupational Safety and Health Administration recommends scheduling frequent rest breaks in shaded or air-conditioned environments. Anyone who becomes overwhelmed by the heat should be moved to a cool and shady area. Heat stroke is an emergency! Call 911. Share your weather photos (if it's safe to do so in your area) – Go to wtae.com/upload or tap the “u local” button in the WTAE app. Download the WTAE app to stay up to date with severe weather alerts and breaking news. Already have the WTAE app? Click here to learn how to get automatic storm and severe weather alerts for your location.