The Philadelphia region's first heat wave of the year began Saturday and will continue through Thursday with heat that will at times reach dangerous levels. Triple-digit high temperatures are in the forecast for Monday through Wednesday, which would break old record highs that were in the high 90s. But what qualifies as a heat wave? Our NEXT Weather team says three consecutive days at or above 90 degrees is considered a heat wave. This heavy heat is being felt across a large swath of the country. By later this weekend, an estimated 140 million Americans will be under the highest level of extreme heat alerts. Click the link in our bio to learn more about how you can stay prepared and protected from the heat. #philadelphiaweather #phillyweather #heatwave #extremeheat