Prolonged, severe drought in much of the southwest has been feeding the heat dome even more than normal because drought-stricken ground bakes even faster under the hot sun. Roys said weather patterns slow down when there's high pressure, so the heat dome is 'kind of like a roadblock,' forcing storms to go around it. High atmospheric pressure from a 'heat dome' has been causing rising temperatures to stick around, while preventing storms from bringing cooling rain. Why is the extreme heat happening before start of summer? PHOTOS: A historic heat wave hit millions this week. While the middle of the country swelters in the heat, the West Coast, Great Lakes, and northeast will experience considerably cooler-than-normal temperatures this weekend, forecasters say. The southeast was also under a heat advisory, with the National Weather Service warning of 'hazy, hot, and humid' weather. On Saturday, southern Minnesota was under an excessive heat watch and other parts of the north-central U.S. Temperatures are 'about 15-25 degrees above average' in the middle of the country according to AccuWeather. 'This heat is on the earlier side, you're looking at potential record-breaking heat across the northern plains, upper midwest this weekend,' AccuWeather senior meteorologist Tyler Roys told USA TODAY. The Central Plains are expected to see highs in the 90s and low 100s, with a heat index that could reach 100-110 degrees during the hottest parts of the day, according to the National Weather Service. Forecasters say the heat wave will gradually move east over the weekend, shifting away from the northern plains. Watch Video: Heat wave to hit Southwest, worsening droughtĪ large swath of the country stretching from Texas to the Dakotas is expected to face another round of scorching temperatures through Monday, possibly even hotter than last week's heat wave.

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