- Temperatures Tuesday in California may go as high as 125
- Last 12 months were the hottest on record, report says
- The first half of 2012 has also set temperature records, NOAA says
- The analysis doesn't include more record-breaking heat from July
(CNN) -- Even as the Midwest, Southeast and Northeast cool a bit, the U.S. Southwest is practically boiling.
The National Weather Service has issued excessive heat warnings for parts of Arizona, California and Nevada through Wednesday, with temperatures forecast to peak Tuesday at 113 degrees in Las Vegas; 113 in Phoenix; 116 degrees in Yuma, Arizona; and 125 degrees in Death Valley, California.
In the Las Vegas Valley, local officials are opening up cooling stations Tuesday to give residents a place to beat the heat. Forecast highs in the 100s will continue into next week.
Triple-digit strategies for staying healthy
The scorching temperatures inflamed the passions of some parents whose sons started preseason football practice in Las Vegas on Monday.
"I just feel that at 111 degrees ... I don't feel that it's even reasonable," a local mom told CNN affiliate KTNV. "I can't believe the school district is even allowing this because it is so dangerous ... These kids should not be playing."
The Clark County School District said it's up to each coach to determine their practice schedule.
"If it is too hot to practice and I feel like kids can't handle it, then we will adjust our plan and either cut practice short or move inside," Liberty High School football coach Richard Muraco said.
Fatima Domingpe applies sunscreen to her face near the Mosaic Fountain in downtown Silver Spring, Maryland, on Saturday, July 7. A record heat wave has been in the area for more than a week. 
Ten-year-old Lilly Hwang-Geddes, left, of Ithaca, New York, plays in a fountain at the Yards Park on Thursday, July 5, in Washington. 
Six-year-old Spencer Hwang-Geddes of Ithaca, New York, cools off at the Yards Park on Thursday. Weather forecast predicted the hot weather will last through Sunday with possible daily triple-digit temperatures. 
A boy enjoys the waterfall in the Yards Park fountain on Thursday. 
Chilren play in the fountain away form Thursday's scorching temperatires at the Yards Park. 
Shannon Mack and Bobby Rush keep cool with their dog, Bubba, in a pool at their apartment in Chicago on Wednesday. 
Keshyra Pitts, 7, plays in the spray of a hydrant in Chicago on Wednesday. 
Lori Bryant holds her 7-month-old nephew Justin Tackett as Marianne Oliver cools him down during the Fourth of July parade in Downers Grove, Illinois. 
Residents find relief from the heat at the McCarren Park pool in Brooklyn, New York, on Tuesday, July 3. 
Abbi Buck, of Cookeville, Tennessee, gulps a bottle of water as sweat drips down her face as she visits the Lincoln Memorial in Washington on Tuesday. 
Katie Kiang finds shelter from the heat to study for the Graduate Record Examinations inside an air-conditioned mall in Silver Spring, Maryland, on Monday. Kiang's home is one of the thousands without electricity after storms hit hard. 
Gene Holmes splashes into a quarry lake after jumping from a rope swing on Monday, July 2, at the Beaver Dam Swimming Club in Cockeysville, Maryland. 
Without electricity to operate the pumps at his gas station in Silver Spring, Maryland, Ken Duckson fills a cooler with ice he cannot sell because his cash registers will not work. 
Aziz Taylor, 11, plays in a water fountain Monday in the Capitol Heights neighborhood of Washington. 
Lifeguard Niko Garcia jumps into a pool in Washington on Monday to try and beat the heat wave gripping the nation. 
A boy plays in a water fountain in Washington on Sunday, July 1, amid a record-setting heatwave in the eastern United States. 
Bryan Moran sprays his dog, Rocky, with water in Washington's Columbia Heights on Sunday. Eastern cities were forecast to approach or break record-high temperatures. 
Linda Gordon, right, finds relief from the extreme heat with an ice pack in Memphis, Tennessee, on Saturday, June 30. 
Residents crowd onto the beach at Coney Island in Brooklyn, New York, in the powerful heat on Saturday. 
Beachgoers lie in the sun at Coney Island on Saturday. 
A boy plays in the ocean at Coney Island on Saturday. 
Workers brave the high heat to repair a storm-damaged roof at the Park Tanglewood apartments in Riverdale, Maryland, on Saturday. 
Beads of sweat roll down Francisco Hernandez's face as he works to repave Hillsborough Street in Raleigh, North Carolina, on Friday, June 29. 
Children play in the water at Six Flags Over Georgia in Atlanta, where temperatures topped 100 degrees on Friday. 
Photos: Extreme heat strikes U.S. 
How long will high temps last? 
Heat wave beginning to break 
Heat Wave: Triple digits Las Vegas Fire and Rescue said it gets as many as 10 extra calls a day when the extreme heat kicks in. But the calls tend to involve the homeless and people not acclimated to the region, not people used to working outside during the summer, affiliate KVVU reported.
Hydration is key, with officials recommending three-times normal water intake.
"When you start to feel thirsty, the body is already damaged," said Las Vegas Fire and Rescue's Tim Szymanski.
Some may think that the excessive heat warnings are, well, a bit excessive given they're being issued for the desert where 100-plus temperatures aren't uncommon.
Not so, says Gary Woodall of the National Weather Service in Phoenix.
"We look at our high temperatures and the low temperatures that we're forecasting," he told affiliate KPHO. An average temperature of 100 degrees for the day is key, since that would limit the body's ability to cool itself.
"We have tried to recognize those cases where we see more of a human impact, and that's what we're trying to represent with those excessive heat warnings," he said.
As the Southwest heated up, the rest of the nation began returning to normal summertime temperatures.
A cold front pushed through the Midwest, as well as parts of the South and Mid-Atlantic states, sparking severe storms and heavy rain in some areas.
Flash flooding hit downtown Greensboro, North Carolina, on Monday night as up to five inches of rain fell, said Darin Figurskey, a meteorologist at the National Weather Service's Raleigh bureau.
"Motorists are encouraged to stay off the roads, if possible," the city said in a statement.
Nearby on Interstate 40, between 20 to 30 cars were stranded due to flooding rains, said Figurskey.
Severe lighting and heavy rain also raked metro Atlanta Monday night.
The front cooled things down.
High temperatures Monday were in the 80s in cities including Chicago, New York, Boston and Washington, where temperatures on Sunday hit 102 degrees and surpassed 95 for the 11th straight day. Even the 91 degrees recorded Monday in St. Louis was a welcome relief.
This cool-down follows a heat wave that roasted much of the country for more than a week and comes as the National Climatic Data Center reported the mainland United States has experienced the warmest 12 months since record-keeping began in 1895.
The report does not take into account blistering heat from this month, with 2,116 high temperature marks either broken or tied between July 2 and July 8 in communities nationwide.
But it does incorporate the warmest March recorded as well as extreme heat in June, which also helped make the first six months of 2012 the warmest recorded of any January-June stretch.
In the last half of June, 170 all-time temperature records were matched or smashed in cities across the lower 48 states. The U.S. State Climate Extremes Committee also is reviewing whether 113-degree temperatures in South Carolina and 112-degree recordings in Georgia qualify as all-time records in those two states.
"There are a lot of things going on that have been very unusual over the last several months," said Dev Niyogi, earth and atmospheric sciences professor at Purdue University.
That includes an outbreak of particularly large wildfires in Colorado, which had its warmest June ever, according to NOAA. Most of that state is experiencing extreme to exceptional drought, which is also true in places as far afield as Arizona and Georgia, according to the U.S. Drought Monitor, run out of the University of Nebraska.
The average temperature for the U.S. mainland in June was 71.2 degrees -- 2 degrees above the 20th-century average. It was the 14th warmest June on record.
The conditions contributed to dozens of heat-related deaths, including 18 in Maryland and 10 in Virginia, according to state officials.
Millions also lost power at one point or another, many of them for several days, because of severe storms that swept east from Indiana to the Mid-Atlantic states starting on June 29.
CNN's Greg Botelho, Joe Sutton, Devon Sayers and Dave Alsup contributed to this report.
