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The lower 48 states are split in more ways than just politics on Monday. A jet stream that is coiled like a snake is causing hot and humid air to surge northeast out of the Great Plains and South, with high temperatures of between 10 to 25 degrees Fahrenheit above average from Minnesota to Massachusetts and points south.

Meanwhile, on the other side of that snake, a dip in the jet stream is bringing unusually cold and wet weather to the West, dumping June snows on the Sierra Nevada mountains, further extending what appears to be a never-ending ski season.

First, there's the heat that tens of millions are coping with from Minneapolis to Chicago on east to Boston, New York City, Philadelphia, Baltimore, and Washington. In Boston, temperatures were soaring into the mid-90s Fahrenheit during the late morning, and could tie or break the daily record of 96 degrees Fahrenheit, which is extremely unusual for early-to-mid-June.

On Sunday, the temperature in Burlington, Vermont reached 95 degrees Fahrenheit, which set a daily record as well as a record for the earliest 95-degree day in history for that city. Other locations that broke or tied records this weekend included Bangor, Maine and La Crosse, Wisconsin.

Monday will be the hottest day of this heat wave, and the week, in the Northeast, since a cold front sagging south from Canada will begin to cool off the region starting on Tuesday. However, the front will not break the heat wave for the Great Lakes, Ohio Valley or Mid-Atlantic, but an overall cooler air mass is likely to sweep into those areas toward midweek.

During this heat event, overnight low temperatures will also be milder than average, especially in urban areas, with low temperatures failing to drop below the mid-70s Fahrenheit in the New York to Washington corridor through Tuesday.

Studies show that heat waves are especially deadly when people aren't given a chance to cool down overnight after a long, hot day. This is part of the reason why those without air conditioning are more vulnerable to heat-related health problems. 

In general, overnight low temperatures have been increasing faster than daytime high temperatures across the U.S. in recent decades, which has to do both with human-caused global warming and urban sprawl. 

Although heat waves in general are a typical summertime occurrence, there is abundant evidence showing that such events are more likely to occur and more severe when they happen, due in large part to human-caused global warming. Scientific studies show a sharply increased risk of severe and deadly heat events around the world. 

For example, a study published in April found that the warming-to-date has already caused the severity and probability of the hottest month and hottest day of the year to increase at more than 80 percent of weather observing sites examined worldwide.

At the same time as the eastern half of the country is dealing with unusual heat for early June, the West is seeing the opposite: A rare cold snap accompanied by mountain snow.

That's a pretty solid ❄️coating of snow since 6pm at @squawalpineops #CAwx #SierraSnow #Juneuary pic.twitter.com/1xjZzbToJk

— Rob Mayeda (@RobMayeda) June 12, 2017

Snow in the Sierra Nevada Mountains in June is not unheard of, occurring at Lake Tahoe, for example, every 5 to 10 years. But accumulating snow in the past few days has helped further extend what has already been a blockbuster ski season at resorts such as Squaw Valley Alpine Meadows.

That ski resort is currently scheduled to remain open until July 4 after a blockbuster winter season.

#snow in #Juneary for the Sierra! Yes, this is real. Measurable snow at #laketahoe in June happens about every 5-10 years. #summerwillreturn pic.twitter.com/0p89PUfSoc

— NWS Reno (@NWSReno) June 12, 2017

#Juneary #Snow in the Sierra! Dumping in Truckee right now at 5800'. More to come the next few hours. Drive safe this "summer" evening. pic.twitter.com/bUKxGNozRD

— NWS Reno (@NWSReno) June 12, 2017

Around the edge of the heat dome in the East, lying at the boundary between the hot conditions to the east and the cool conditions to the west, lies the threat of severe thunderstorms with large hail, damaging winds and tornadoes.

The Storm Prediction Center in Oklahoma has highlighted the area from Montana to Wisconsin as being at heightened risk of severe storms on Monday, including an area at "moderate risk," the second-highest level, in parts of Montana, South Dakota, and Nebraska.

On Sunday, complexes of thunderstorms rumbled across the northern Great Lakes and into Canada, bringing large hail and damaging winds.

Live report @kare11 @IvoryHecker in Coon Rapids piles of hail remain on the sides of streets. #KARE11weather pic.twitter.com/Tkv2GrkGCs

— Matt (@mattpassolt) June 11, 2017

The trail of destruction was long enough for one of these storm systems to qualify as a derecho (pronounced "de-REY-cho"), which refers to a long-lived severe thunderstorm that brings damaging straight-line winds.

It knocked out power to more than 100,000 across Minnesota, including in the Twin Cities, and dumped so much hail that people turned to snow shovels and tractors to clear the streets and sidewalks.

For areas that could use a cooling downpour, though (I'm looking at you, midtown Manhattan), there will be none to be found on Monday.

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