Fires in Arizona, New Mexico and California have raged throughout the weekend, stoked by hot and dry climates

Performance charts for most modern aircraft have not been produced for air temperatures greater than 120°F and so flights at Sky Harbor International airport would have to be suspended until the mercury fell

Phoenix could face airline and train delays, as well as, power failures and heat wave victims as temperatures soar

New Mexico, southern Nevada, Southern California and other parts of Arizona are expected to see temperatures as much as 20 degrees above average — up to 110 degrees

Triple-digit temperatures are nothing new for the U.S.'s deserts but the weather can cause cities to shut down

On Saturday, a 25-year-old Phoenix man also died of heat exposure while hiking in neighboring Pinal County

She had set out around 6 a.m., carrying water, but became exhausted about three hours later, then could not breathe

A 28-year-old woman died after she became unresponsive while mountain biking with friends in north Phoenix


Four people have lost their lives as the southwestern United States bakes under some of the highest temperatures on record, close to 120 degrees.

A 28-year-old woman became unresponsive while mountain biking with friends in north Phoenix. She had set out with two friends around 6 a.m., carrying water, but became exhausted about three hours later, then could not breathe.

On Saturday, a 25-year-old Phoenix man died of heat exposure while hiking in neighboring Pinal County.

Later Sunday, two hikers, a man and a woman in their early 20s hiking in Pima County left the trail without taking along water and had to be rescued by helicopter, authorities said.

The woman died before deputies arrived, and the man was being treated at a hospital.

In a separate incident, one man died and another remained unaccounted for Sunday night after their hiking group was overcome in Ventana Canyon near Tucson.

'If we are going to 115 or 120, people need to realize they are really in a life-threatening situation if they don't wet themselves down and drink water,' Kevin Kalkbrenner, Phoenix's director of homeland security and emergency management, told ABC News.

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A Hotshots member from the U.S. Forest Department sets a back fire while battling the the so-called 'Sherpa Fire', which has grown to over 1100 acres overnight, in the hills near Goleta, California

An aerial fire boss flies a jet down a canyon, toward scorched terrain At the Sherpa Fire near Santa Barbara, California

Warning: The National Weather Service tweeted that the heatwave began on Sunday urging people to stay cool and keep hydrated

Red fire retardant dropped by aircraft covers thick chaparral brush as a scorched landscape smolders in the distance.The so-called Sherpa fire in the Los Padres National Forest is raging full speed, fanned by strong winds, prompting authorities to declare a state of emergency

The fire is the tourist region's largest since 2009, a Santa Barbara spokeswoman said

Firefighters douse a fire under State Route 2 after a brush fire swept through threatening homes in Los Angeles on Sunday

Excessive heat warnings blanketed Southern California and Arizona, where temperatures soared into the triple digits Sunday and were expected to remain there until Monday, according to the National Weather Service. 'The interior areas will remain dangerously hot,' the NWS said.

At least five major wildfires across the desert Southwest are being tackled. A heatwave in Phoenix, Arizona, could see airplanes unable to take off and power grids strained or stalled as transmission lines struggle to keep the system cool.

Triple-digit temperatures are nothing new for the U.S.'s deserts, but the Arizona capital is coming painfully close to its all-time high record of 122 degrees.

The heat will remain constant in the West and expand into the middle of the country by midweek, said Reynolds Wolf, a meteorologist for The Weather Channel.

'It's like you take a salt shaker of madness and sprinkle it' over the western half of the country, Wolf said.

Los Angeles firefighters say they have contained the fire in the densely populated neighborhood along a freeway

Fire converts thick chaparral brush covered mountainsides to grey ash at the Sherpa Fire near Santa Barbara, CaliforniA

Members of the elite Dalton Hotshots crew drink at the end of a shift at the Sherpa Fire near Santa Barbara, California

Arizona (pictured) is struggling through near-record-breaking heat waves that have seen the capital city of Phoenix hitting triple-digit degrees

This year highs of 120 degrees and dry conditions have stoked massive fires that have burned 10,000 acres of land in Show Low, Arizona

Arizona's hottest day on record was in 1990 when temperatures hit 122 degrees, said Nancy Selover, and the weather this week could come close to breaking that record

COULD FLIGHTS FROM PHOENIX BE GROUNDED? On June 26, 1990 Phoenix Sky Harbor airport set a record with temperatures reaching 122°F. At the time, airlines stopped taking off and landing for part of the day, because at the time they did not have aircraft performance charts for temperatures that high. Even today, performance charts for most modern aircraft have not been produced for air temperatures greater than 120°F. If Phoenix were to post a temperature greater than 120°F this week, takeoffs and landings would once again be suspended by Sky Harbor International Airport. Advertisement

Residents have been warned to watch for signs of heat stroke or illness, which include thirst, red skin, cramping, exhaustion and a lack of sweat, as the blazing temperatures climb.

One elderly woman has already succumb to the heat this month after exposure in her backyard, officials confirmed.

Last year, the summertime heat contributed to the death of 84 people in Arizona.

Hikers have been asked to be off of trails by noon and the Phoenix parks department has stationed extra rangers around the hiking areas.

Because excessive heat can throw off performance calculations, airlines will have to monitor temperatures to decide if they can safely take off.

Flights could be delayed until the weather cools down, but it is unclear what officials will decide.

Arizona's hottest day on record was in 1990 when temperatures hit 122 degrees, said Nancy Selover, state climatologist. ABC News reported.

At that time, airlines were forced to ground flights out of Phoenix Sky Harbor International Airport, she said.

Even though they're designed with heatwaves in mind, the Valley Metro Rail lines expand in the blisteringly hot weather and cotton crops beg for more water while state lakes and reservoirs begin evaporating.

Power companies must be vigilant to ensure outages are kept at bay and extra maintenance crews will be on duty.

In Arizona (pictured), more than 5,500 acres have burned and the community of Cedar Creek has been evacuated and thousands more have been told to prepare to leave

Residents have been warned to watch for signs of heat stroke or illness, which include thirst, red skin, cramping, exhaustion and a lack of sweat, as the blazing temperatures climb

However, it's people who will be the hardest to prepare as that is where the heat's biggest impact is felt.

Centers will be passing out cool water for anyone - especially the homeless - who passes their doors.

'We're a church so it's what God called us to do,' pastor Jerry Savocchio, whose church is one of 50 cooling stations in Maricopa County, told ABC News.

Pets can also be subjected to painful heat when they come in contact with the ground outdoors, which can reach surface temperatures of 150 to 170 degrees.

Glendale Fire Department firefighter Chris Greene, right, gets a case of water from service worker Edi Marroquin, left, from the dozens of cases of water at the Glendale Fire Department Resource Center as they prepare for the record-setting heat predicted for the weekend.

Glendale Fire Department firefighter Chris Greene carries a case of water as he walks past dozens of cases of water at the Glendale Fire Department Resource Center in preparation for expected record-setting heat.

The Sunday forecast (pictured) shows four states - Texas, Arizona, New Mexico and Nevada - topping out at triple-digit temperature highs

As temperatures in at least Texas and New Mexico drop back down into the double digits, Arizona and Nevada will stay stoked in the 100s

'If it's too hot to walk in your bare feet it's too hot to make your dog walk on it,' said Melissa Gable, spokeswoman for Maricopa County Animal Care and Control.

In three states, including Arizona, massive wildfires stoked by the heat have cause thousands to evacuate and damaged even more thousands of acres of land.

In Arizona, a fire near Show Low has grown to 10,000 acres and - like the Dog Head Fires in New Mexico - has caused evacuations. Thousands of residents in the area are in pre-evacuation mode.

Firefighters battle an expanding wildfire at the Sherpa Fire near Santa Barbara, California (pictured). A fire in the Los Padres National Forest had expanded to two square miles

Fires raging in California (pictured), New Mexico and Arizona have grown in size and burned thousands of acres of land

'Humidity values less than 15 per cent and dew points as low as the single digits will be present and persistent across a large portion of the Southwest through at least Sunday,' said meteorologist Jonathan Belles

So far only a dozen people have been forced to leave their homes.

In California, a fire spread by the 'Sundowner' winds has caused a massive 6,000 acre fire to spread in the Los Padres National Forest in Santa Barbara County.

Mandatory evacuations are in place and the state's main highway U.S. 101 had to be shut down for hours on Friday as firefighters battled the blaze.

A state of emergency has been declared in New Mexico as the 'Dog Head Fire' tripled in size to 17,000 acres on Saturday.

Manzano Mountains, south of Albuquerque, has had forced evacuations due to the growing blaze caused by wind and high temperatures.

In New Mexico 24 homes and 21 other minor structures have been destroyed.