WASHINGTON — A heat wave spreading across the United States is leaving few places to hide. Not even the cool of night.

By Friday afternoon, all but one of the lower 48 states had hit 90 degrees somewhere, with only Washington state offering cooler comfort. 

For much of the country, the heat is expected to get worse over the weekend.

In all of northwest Ohio and southeast Michigan, a National Weather Service Heat Advisory that took effect Friday morning was scheduled to continue into Sunday evening because of combined high temperatures and high humidity that pose risk to vulnerable people.

Temperatures in the Toledo area are expected to reach the low to mid-90s today and Sunday. The temperatures and high humidity will create “heat index” readings between 100 and 104 both days, according to the National Weather Service.

On Friday, the high hit 91 at Toledo Express Airport and 93 at Toledo Executive Airport in Wood County.

The high at The Blade building was 93.

The extra-hot weather will ease a bit next week for large sections of the country, but the forecast for the next three months isn’t exactly promising, according to the National Oceanic and Atmospheric Administration.

For the first time in more than 20 years, the Climate Prediction Center map is shades of one color: orange for above normal temperatures.

The map usually varies. But the outlook for August, September, and October is for above normal everywhere.

Center climate scientist Dan Collins said the center’s archives go back to 1995 and they’ve never seen this for the entire United States — including Alaska and Hawaii. That doesn’t mean a three-month heat wave, just on average warmer than normal temperatures through October.

“Unusual indeed,” Mr. Collins said. 

Scientists haven’t calculated if man-made global warming from the burning of fossil fuels is a factor in the current heat wave, but they said it has been a factor in most recent ones. 

What’s happening now is a ridge of high pressure has just spread over most of the United States. That keeps clouds and cooling away and pushes warm air down.

Add to that the humidity, which makes everything feel stickier. It’s coming with warmer ocean water, especially from a hotter-than-normal Gulf of Mexico, said Jeff Masters, meteorology director of the private Weather Underground. 

The high heat and humidity will move from the Corn Belt toward the Southeast over the weekend, according to the National Weather Service.

On Monday, the weather service forecasts that nearly all of the Lower 48 states could hit 95 on the heat index , which factors in humidity. About 30 states are forecast to hit 100.

The high temperature average for the lower 48 states was 92 degrees both Thursday and Friday, the warmest since June, 2012, said meteorologist Ryan Maue of the private WeatherBell Analytics service.

Not even the cool of night is helping because temperatures aren’t dropping as much as they normally do. 

That’s a health issue because the human body relies on the evening coolness for relief, said Greg Carbin, a forecast chief for the weather service’s Weather Prediction Center.

People at risk of heat-related illness include people working outdoors or otherwise exposed to direct sunlight for extended periods; the elderly and young children, and people who lack air conditioning in their homes or workplaces.

Locally, a heat advisory is in effect until 8 p.m. Sunday. 

National Weather Service forecasters predict midweek highs next week in the Toledo area in the upper 80s.

The Area Office on Aging of Northwestern Ohio announced extended hours today for emergency cooling stations at its senior centers in Lucas and Wood counties. The locations and hours are:

• East Toledo Family Center, 1020 Varland Ave., Toledo: 11 a.m. to 5 p.m.

• Oregon Senior Center, 4350 Navarre Ave., Oregon: 9 a.m. to 5 p.m.

• Zablocki Senior Center, 3015 Lagrange St., Toledo: 11 a.m. to 5 p.m.

• Wood County Senior Center, 305 N. Main St., Bowling Green: 11 a.m. to 8 p.m.

The city of Toledo, meanwhile, announced that municipal pools  and the Savage Park splash pad will be open from noon to 6 p.m.

While they expect warmer-than-normal wea-ther, forecasters did not predict record heat during the coming days. Record highs for all remaining days in July are 97 or higher, including today’s 99, set in 1933, and Sunday’s 103, set in 1934.

Worldwide, the first six months of this year have continued to shatter heat records, putting 2016 on track to be the Earth’s hottest year on record, the World Meteorological Organization said Thursday.

The United Nations-linked body said in a report that June, 2016, was the 14th consecutive month of record heat around the planet and the 378th consecutive month with temperatures above the 20th-century average.

First Published July 23, 2016, 4:00 a.m.