Where are the highest chances for a hot summer in 2017?

May 18, 2017

Schools are letting out, Memorial Day is nearly here, and for many Americans that means the unofficial start of summer. And if it's summer, then it 's time to start paying attention to the risk of extreme heat. According to NOAAs summer outlook, most of the United States is favored to have a hotter than average summer in 2017. Only in the Great Plains do forecasters think the chances for a cool or a normal summer are equal to the chances of a hot summer. Everywhere else; from Alaska to southern California, and from Maine to Texas—odds are tilted toward well above average warmth. The absolute highest chances for a much warmer than usual summer are in Hawaii.

Summer Temperature Outlook

Map showing the odds of well above average temperature during summer of 2017. Well above average means "in the upper third of the 1981-2010 climate record." White shows areas with equal chances for any of the possible climate outcomes (cool, warm, or normal). Darker red colors mean higher chances (greater confidence). NOAA Climate.gov map, based on data from the Climate Prediction Center.

Darker colors mean higher chances, not bigger departures from average temperature

The orange and red colors on the map show where the chances of a much warmer than average summer exceed 33%. The darker the color, the greater the chances. Areas colored white mean that forecasters think all three temperatures possibilities—colder than normal, near normal, and hotter than normal—have an equal chance of occurring. In other words, the climate system is not leaning one way or another.

When it comes to heat stress, nighttime matters, too

There is more than one way to define a heat wave, since what counts as extreme heat depends not just on location and air temperatures, but also on how humid it is, whether there is a breeze, and how sunny or overcast it is. One factor that public health experts say is critical is the overnight low temperature. When it does not cool off at night for at least a few hours, an extended hot spell can become especially dangerous. It is a situation that global warming is making more common.

Summer Temperature Outlook

The percent of the contiguous United States recording extremely warm overnight lows in summer (peach bars) has been increasing over the past century. Meanwhile the percent of the contiguous United States recording extremely cool overnight lows (blue bars) is getting smaller. NOAA Climate.gov graph, based on data from the Climate Extremes Index tool from the National Centers for Environmental Information.

NOAA, U.S. Department of Commerce, News & Features.