Heat scorches eastern U.S. as snow (yes, snow) falls in California
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.
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.