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ATLANTA — Heat is normal during the summer, but this year's has been anything but normal and, halfway through the season's hottest month, it's clear this one is for the record books.
Hundreds of cities in nearly every U.S. state — including parts of Alaska and Hawaii — are on track for one of their 10-warmest summers on record. About 100 of these cities are enduring their hottest start to summer on record.
The deadly heat has not been unexpected. Forecasters have been warning of a searing summer for months due to the troubling combination of a budding La Niña and a world warming due to fossil fuel pollution.
Last summer was the warmest on record globally and one of the warmest for several states. But so far, this summer has felt even worse for many in the U.S. Extreme heat has baked almost all of the Lower 48 so far this summer, but the worst of it has concentrated in the East Coast states and West.
Average daily temperatures — calculated by taking the average of each day's high and low — have soared several degrees above normal for hundreds of cities since June 1. These temperatures are a more complete indicator of how hot the season has been, as they factor in both hotter days and warmer nights.
Summer nights in the US have been warming nearly twice as fast as summer days since records began in the late 1800s, according to data from NOAA. Warmer nights increase the danger of heat by compounding heat stress through a reduction in the amount of time the body has to cool down naturally.
Las Vegas is experiencing its hottest summer on record and holds the top spot in the entire country. Many of the cities experiencing the most exceptional summer heat are in the West, notably in or near California's Central Valley. Searing heat there has been relentless since it started in early June.
On the opposite coast, a historic mid-June heat wave has only been spelled by brief bouts of relief. Dozens of cities from New England to the Mid-Atlantic are experiencing their hottest start to the summer on record, including Washington, D.C., which just smashed a high temperature record Tuesday when it hit 104 degrees.
Some of the most abnormal heat in the region is focused in New England and New York state.
The South has also sweltered under more than its fair share of historic heat so far this summer. Atlanta and Tampa, Florida, are both on pace to record their hottest summer on record. For some locations in the region, it's the second consecutive year summer has had a blistering start.
Last summer ended up quite warm for the Lower 48, but the worst heat was confined to the Gulf Coast. By mid-July last summer, the season was pacing as one of the warmest on record for cities nearest the coast, including cities like New Orleans, Houston and Brownsville, Texas.
But in other parts of the country, last summer was downright cool compared to this year's extreme heat.
Washington, D.C., is currently on track to record its hottest summer on record, but it was only the 44th-warmest summer by this time last year. Sacramento, California, is experiencing its hottest start to summer on record. But this time last year California's capital city was experiencing is 62nd-warmest summer.
Forecasts for the rest of the season aren't cool, either.
Despite some upcoming brief periods of respite, much of the Lower 48 is expected to endure above-average temperatures through August and into September, according to the Climate Prediction Center.
