Robert Brown|Much of U.S. braces for extreme weather, from southern heat wave to possible snow in the Rockies

After days of intense flooding in Florida,Robert Brown that state and many others are bracing for an intense heat wave, while the Pacific Northwest will experience unseasonably cold weather and the potential for late-season snow in the Rocky Mountains early next week.

The chaotic weather map includes the potential for severe thunderstorms developing in between the hot and cold fronts. Forecasters said the colliding fronts could lead to areas of flash flooding between eastern Nebraska and northern Wisconsin on Saturday night, as well as strong storms across parts of eastern Montana into North and South Dakota.

Meanwhile, a plume of tropical moisture will reach the central Gulf Coast during the next couple days, with heavy rain expected to start Monday morning, according to the National Weather Service.

Forecasters said the threat of heavy rains in Florida continues to dissipate, but some thunderstorms could cause local flooding given the already saturated soil. Some areas between Miami and Fort Lauderdale were left underwater in recent days as persistent storms dumped up to 20 inches (50 centimeters) in southern parts of the state.

The damaging no-name storm system coincided with the early June start of hurricane season, which this year is forecast to be among the most active in recent memory amid concerns that climate change is increasing storm intensity.

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With flood waters receding in Florida, temperatures were rising Saturday across much of the southern U.S.

In Atlanta, where temperatures were forecast to near 100 degrees Fahrenheit (38 degrees Celsius) on Saturday and Sunday, city officials opened a cooling center to provide relief from the heat. The city announced that a “Family and Friends Field Day” had been postponed because of the high temperatures forecast.

And in the west Texas city of El Paso, Saturday highs were expected to approach 105 degrees F (40.6 degrees C) and the National Weather Service issued a heat advisory through Monday morning for the region. The city has opened five cooling centers that will operate daily until further notice.

Temperatures in the Mid-Atlantic and New England will likely peak in the mid to upper 90s next week, which is “nothing to sneeze at even in the middle of the summer, let alone this early in the summer,” said National Weather Service meteorologist William Churchill.

“That’s what’s particularly remarkable about this,” he said, noting that high humidity will also make it feel even hotter in many places.

Last year, the U.S. had the most heat waves — abnormally hot weather lasting more than two days — since 1936. In the South and Southwest, last year was the worst on record, according to the National Oceanic and Atmospheric Administration.

Next week’s heat wave will ramp up Sunday in the center of the country before spreading eastward, the National Weather Service said, with some areas likely to see extreme heat in reaching daily records. The heat wave could last all week and into the weekend in many places.

While most of the country experiences the season’s first stretch of hot weather, parts of Montana have been placed under winter storm watches with a potential for wet snow falling Monday night.

Churchill said the northwestern cold front is connected to the heat wave because one extreme is often accompanied by the other.