No state was cooler than average and five states - Texas, Oklahoma, Kansas, Nebraska, and Missouri - experienced record warmth for the period.

While much of the Northeast experienced extreme rainfall and flooding at the end of June many other areas continued below normal rain and snowfall.

As of June, 45 percent of the contiguous U.S. was in moderate-to-extreme drought, an increase of 6 percent from May.

Dry conditions spawned more than 50,000 wildfires, burning more than 3 million acres in the continental U.S., according to the National Interagency Fire Center.

Worldwide, it was the sixth warmest year-to-date since record keeping began in 1880.

The National Weather Service issued excessive heat warnings for Las Vegas, Chicago, St. Louis and Tulsa, Okla. Excessive heat watches were issued for the Philadelphia area and New Jersey, where thermometers made it into the 90s Sunday in a rehearsal for highs of 100 degrees Monday.

"I could use a pool out here," Doreen Venick, 36, said Sunday as she took shelter in the shade of a small tree with her two children and her sister at a children's festival in Brick, N.J.

Officials in Chicago, where a 1995 heat wave killed 700 people, opened 24-hour cooling centers and pleaded with people to check on elderly neighbors. No heat-related deaths were reported in the city by Sunday afternoon as temperatures approached 100 in parts of the state Sunday.

Organizers of Gay Games VII, a sporting event that has drawn about 12,000 gay and lesbian athletes to Chicago, said outdoor events were going ahead as planned with hydration stations, tents and medical teams ready if needed.

Chicago hit 92 by 1 p.m., with humidity of about 50 percent, but it didn't bother Frank Lee of Manoa, Hawaii, who was competing in the event's tennis matches and planned to drink plenty of water and eat bananas.

"Oh, I love it balmy," Lee said. "But maybe it's a little too hot."

A large high pressure area centered over much of the mountain states and extending into the Midwest was pumping hot air from Mexico across the desert Southwest and into the Midwest, said Rob Handel, a weather service meteorologist in Chicago.

Even the Colorado mountain town of Frazier, which sits at 8,550 feet and likes to claim that it is the nation's ice box, was in the upper 80s during the weekend.

"It's not supposed to be hot like this. Lately there have been evenings when you could sit outside at 10 p.m. without a coat. All my life I couldn't do that," said Connie Clayton, 58, a lifelong resident of Frazier.

The mile-high city of Denver hit a record high of 101 on Saturday.

South Dakota posted some of the nation's highest temperatures with a reading Saturday of 115 at Pierre, the state capital, and an unofficial report of 120 outside the town of Usta in the state's northwest corner.

"There's a lot of records that are falling across the state," said Todd Heitkamp, a weather service meteorologist in Sioux Falls.

In Arizona, Sunday's high was forecast at 110, not enough to rate an extreme heat advisory in the desert metropolis.

In Oklahoma, where temperatures also have been rising above 100, officials were investigating a possible heat-related death and reported more than 40 heat-related calls to emergency medical services in Oklahoma City and Tulsa.

Southern California joined in the heat wave, with temperatures over 100 degrees adding to the problems facing firefighters battling huge wildfires. Lancaster hit 109 on Saturday and Pasadena recorded 101, and Southern California Edison reported a record for weekend power use as air conditioners were cranked up.

In New Jersey, at the other end of the country, temperatures were expected to reach 100 degrees on Monday. An excessive heat warning was issued for several counties.

Hot, sticky air also covered parts of the Southeast. In Georgia, temperatures have soared to near-record highs, with six cities posting temperatures of 100 degrees or higher on Saturday.

"They might be an early warning, an indicator of how natural systems will respond," said ecologist William Bowman, director of CU's Mountain Research Station at Niwot Ridge, northwest of Nederland.

To spot changes in tundra vegetation caused by warming, permanent monitoring plots are being established this summer atop three peaks within the city of Boulder watershed, along the Continental Divide.

The peaks - 12,609-foot Albion, 13,150-foot Arikaree and 13,276-foot Kiowa - were selected in part because the watershed is closed to the public, so summit-area vegetation is relatively untrammeled.

Sixteen one-square-meter plots will be staked out in the alpine tundra just below the summit of each peak - four in each of the four cardinal directions. Temperature and vegetation will be monitored periodically.

The National Science Foundation provided $7,000 this year to install the plots near Niwot Ridge.

Similar mountaintop plots will be set up this summer on peaks in southwestern Colorado's San Juan Mountains - possibly near Red Mountain Pass, said Chris Landry, executive director of the Center for Snow and Avalanche Studies in Silverton.

The Colorado peaks will be part of an international network of long-term alpine monitoring sites called GLORIA, which stands for Global Observation Research Initiative in Alpine Environments. Established in 2001, the program has grown to more than 30 sites around the world, from the poles to the tropics.

On Friday morning, Bowman and his research assistant, John Murgel, drove five miles on a rugged dirt road, then hiked three miles to the Albion summit. There they began the somewhat tedious task of counting, naming and recording every plant in their newly established tundra plots.

On Colorado's highest peaks, the alpine tundra community is a ground-hugging mix of some 350 species of grasses, sedge, wildflowers and other forbs, moss, lichen and low shrubs such as dwarf willow and birch.

Sixteen plant species were found in the first four one-meter-square Albion plots checked Friday. They included the buttercup-like alpine avens; the alpine fescue, a common grass; the nailwort, a moss-like "cushion" plant; dwarf sunspot, a miniature sunflower; Carex rupestris, sometimes known as the curly-leaf sedge; and alpine parsley, a forb.

The snows of Arapaho Glacier gleamed to the west. The Denver metropolitan area was lost in haze to the east. The only sounds were the roar of a waterfall, the chirp of pikas and birds, the buzz of black flies, the drone of distant airplanes, and Bowman's voice as he recited the Latin scientific name of each plant while Murgel recorded it in a notebook.

Climate models suggest that by 2100, Colorado could warm 3.6 to 7.2 degrees Fahrenheit, largely due to the buildup of heat-trapping "greenhouse" gases emitted when fossil fuels are burned.

In some parts of the West, conifer forests are expected to gradually move to higher elevations as the climate warms. But University of Wyoming tree line researcher William Baker said that's unlikely to happen in Colorado, unless the warmth is accompanied by additional moisture.

"Across most of that tree-line area, it's a pretty severe place for them, and they need more moisture to be able to regenerate and really grow, and particularly to move up into the alpine," Baker said.

Tundra plants will likely provide a better climate-warming red flag, Bowman said Friday.

Along the tundra-forest boundary in the Front Range, early indications of a response to warming could include upward migration of shrubs - various willows and blueberry, for example - and nonnative weeds such as dandelions.

The number of tundra species might increase initially, as intruders move into previously inaccessible areas. But as the decades pass, extinction of alpine plants is possible, accompanied by a decline in alpine species, Bowman said.

That decline, in turn, could affect wildlife that rely on tundra plants for sustenance.

Illinois Gov. Rod Blagojevich said Sunday the state would make more than 130 office buildings available as cooling centers beginning Monday. Minnesota Gov. Tim Pawlenty had ordered the National Guard out to help firefighters as temperatures even in the normally cool northern part of the state pushed 100 degrees amid very dry conditions.

The National Weather Service issued excessive heat warnings for Las Vegas, Chicago, St. Louis, Philadelphia, Tulsa, Okla., and parts of New Jersey, where thermometers made it into the 90s Sunday and were expected to reach 100 degrees Monday.

"I could use a pool out here," Doreen Venick, 36, said Sunday as she took shelter in the shade of a small tree with her two children and her sister at a children's festival in Brick, N.J.

Officials in Chicago, where a 1995 heat wave killed 700 people, opened 24-hour cooling centers and pleaded with people to check on elderly neighbors. No heat-related deaths were reported in the city by Sunday afternoon as temperatures approached 100 in parts of the state Sunday.

Organizers of Gay Games VII, a sporting event that has drawn about 12,000 gay and lesbian athletes to Chicago, said outdoor events were going ahead as planned with hydration stations, tents and medical teams. Two triathletes were treated for heat-related illnesses.

Chicago hit 94 by 3 p.m., but it didn't bother Frank Lee of Manoa, Hawaii, who was competing in the event's tennis matches and planned to drink plenty of water and eat bananas.

"Oh, I love it balmy," Lee said. "But maybe it's a little too hot."

A large high pressure area centered over much of the mountain states and extending into the Midwest was pumping hot air from Mexico across the desert Southwest and into the Midwest, said Rob Handel, a weather service meteorologist in Chicago.

Even the Colorado mountain town of Frazier, which sits at 8,550 feet and likes to claim that it is the nation's ice box, was in the upper 80s during the weekend.

"It's not supposed to be hot like this. Lately there have been evenings when you could sit outside at 10 p.m. without a coat. All my life I couldn't do that," said Connie Clayton, 58, a lifelong resident of Frazier.

The mile-high city of Denver had two straight days of record highs, hitting 103 on Sunday and 101 Saturday.

South Dakota posted some of the nation's highest temperatures with a reading Saturday of 115 at Pierre, the state capital, and an unofficial report of 120 outside the town of Usta in the state's northwest corner.

"There's a lot of records that are falling across the state," said Todd Heitkamp, a weather service meteorologist in Sioux Falls.

The mercury again topped 100 degrees Sunday across much of South Dakota, and in North Dakota, the temperature hit 106 degrees in Bismarck and 100 in Dickinson.

In Arizona, Sunday's high was 109, not enough to rate an extreme heat advisory in the desert metropolis.

In Oklahoma, where temperatures also have been rising above 100, officials were investigating a possible heat-related death and reported more than 40 heat-related calls to emergency medical services in Oklahoma City and Tulsa.

Southwest Oklahoma caught the worst of the heat Sunday: Lawton had a high temperature of 106 and Hobart and Frederick topped out at 104 degrees. The state's weeklong forecast calls for highs ranging from the mid 90s up to 106 degrees.

Several people were treated for heat-related illnesses Saturday at the St. Vincent Medical Center in Toledo, said Dr. Greg Hymel, an emergency room physician. The National Weather Service issued a heat advisory for the area Sunday, with temperatures reaching 91.

Officials with Middletown City Schools, halfway between Cincinnati and Dayton, Ohio, canceled the last week of elementary classes for the summer because of the heat. The two buildings where those classes are held lack air conditioning, district spokeswoman Debbie Alberico said.

California joined in the heat wave, with temperatures forecast to rise above 100 degrees Monday from the Mexican border to as far north as Redding and near the coast. State highs are expected to be 115 degrees near Barstow and 112 near Parkfield, said meteorologist Will Pi.

Power grid managers asked California residents to conserve electricity, predicting demand will spike for air conditioners.

Hot, sticky air also covered parts of the Southeast. In Georgia, temperatures have soared to near-record highs, with six cities posting temperatures of 100 degrees or higher on Saturday.

Temperatures in downtown Rapid City missed the all-time record of 107 by one degree, Johnson said.

There were also record highs of 116 in Philip and 111 in Interior, and The Associated Press reported 115 degree temperatures in Pierre, 114 degrees in Mobridge and 108 in Mitchell.

"There were a few places where we didn't quite reach triple digits, but pretty much all of the prairie areas east river were well above the 100 degree mark," Johnson said.

Johnson said the sweltering temperatures and high winds will increase the already high level of fire danger. "We will still be at 'red flag' conditions tomorrow," Johnson said. "We probably won't see a cool down until the end of next week, so we still have several days of hot, dry weather ahead of us."

Although many opted to spend Saturday inside with the air-conditioner, the extreme temperatures did not deter thousands of people from attending the Hills Alive Christian music festival held in Memorial Park in Rapid City.

"I'm sure that there are some people that stayed away because of the heat, but I also know that people know what happens at this festival, and they'll come out to see the artists that they want to see," said Suzanne Happs, program director for KLMP radio and volunteer organizer at the festival.

Happs said about 30,000 people attended the festival in 108-degree heat last year, and they were hoping for more people at this year's event.

"It's been a progression," Happs said. "We had 22,000 the year before last, 30,000 last year, even in the stifling heat. We're hoping that it just keeps growing."

"It's going to take hotter temps than this to keep me away," Susan Keller of Chamberlain said.

Younger attendees opted to skip the music and cool off in Memorial Lake, and about 25 children chose to swim in the park's water fountain.

Despite the crowd's overall enthusiasm, the heat did take its toll on a few of the spectators.

Dr. Jeffrey Buckau, who was voluntarily manning the festival's first-aid tent, said they had at least four heat-related incidents on Saturday.

The most significant was a woman suffering from heat stroke. "Her temperature was going up, her blood pressure was dropping, her pulse rate was going up and she was throwing up," Buckau said.

Buckau was working with volunteer EMTs to treat patients suffering from the heat.

With only the slightest dip in temperatures in the forecast, Buckau recommended that those attending the festival today stay out of the sun, keep physical activity to a minimum and drink plenty of water.

Fire officials Saturday reported some progress in battling the blazes, which covered more than 110 square miles in Southern California about 100 miles east of Los Angeles.

A 60,000-acre fire was 50 percent contained, its eastern flank no longer a problem but its western side still a major concern. An evacuation remained in effect in one area, but were lifted in several others. Ignited by lightning a week ago it roared to life a few days later, destroying 58 desert homes.

An adjacent complex of fires that merged with the larger fire Friday grew to more than 15,572 acres but was 10 percent contained. Crews protected a handful of homes in a canyon, but there were no evacuations.

The fires were burning below the flanks of the San Bernardino Mountains, but as of Saturday were not considered immediate threats to resort communities in the Big Bear Lake region atop the range.

"There is no evacuation or potential evacuations at this time for Big Bear," said Wayne Barringer, a fire information officer for the California Department of Forestry.

Firefighters were being airlifted to the inaccessible western flank of the larger fire or were being driven in and hiking the rest of the way. Some crews were having to camp in remote locations.

Cate Baker-Hall, 55, an artist, said her three-story home burned to the ground. She lost a collection of more than 100 paintings, lithographs and other art, and a manuscript of a book she had just completed on the 1960s British band, The Zombies, she said.

The house "is just gone," she said. "I'm trying to take the Buddha approach and deal with today. There's only so many tears you can cry."

Gov. Arnold Schwarzenegger, who visited a command post at Yucca Valley High School with wife Maria Shriver, said their helicopter tour had flown close enough to see firefighters working on the ground.

"It is a huge fire. It is really extraordinary how quickly it has spread out," he said. "And that's why I say it is very dangerous and they have to contain it as quickly as possible."

Fire commander Rick Henson told the governor the threat to structures in Yucca Valley communities was over, but he noted that when the fires merged they began moving a bit north and west, toward the mountains.

"It's really not moving toward Big Bear right now but it is a threat," he said.

Elsewhere in Southern California, a 500-acre blaze in Redlands was 20 percent contained after destroying one building. It broke out Friday night and threatened 100 homes but there were no evacuations.

In San Diego County, a 260-acre fire in Cleveland National Forest was fully contained and hand crews were finishing off the remains of a 20-acre blaze that spread over both sides of the U.S.-Mexican border in Tecate, said state fire spokeswoman Audrey Hagen.

Meanwhile, in southern Montana, firefighters mostly east of Billings were battling major large fires that charred about 185,000 acres. About 125 homes were potentially threatened, officials said.

In Wyoming, a wind shift helped firefighters keep a wildfire from advancing toward Devils Tower National Monument. Four fires about 5 miles southwest of Devils Tower have burned about 13,700 acres - about 21 square miles - of mostly shrubs and ponderosa pine. About 10 percent of the fires were contained.

In northern Minnesota, a more than 1,400-acre fire in a wilderness area near was worrying authorities, who feared it could be fueled by millions of trees that blew down in a 1999 storm. Temperatures were near 100 in nearby Duluth.