The latest on extreme weather in the US

Extreme temperatures can turn deadly, quickly in the United States, killing more than 700 people every year, according to the US Centers for Disease Control and Prevention. Nearly one-third of the US population is under heat warnings or advisories on Tuesday with no sign of the above-normal temperatures letting up next week, according to the National Weather Service Climate Prediction Center.

While dehydration is a common concern, “the most worrisome consequence” of high heat is heat stroke, said Dr. Scott Dresden, an assistant professor of emergency medicine at Northwestern University. Heat stroke can cause confusion, seizures and even death, he said.

Humidity is one of the main things that can affect your body's ability to cool itself off, according to the CDC.

"When the humidity is high, sweat won’t evaporate as quickly. This keeps your body from releasing heat as fast as it may need to," the CDC says.

Personal factors can also play a role in very hot weather. These are things like "obesity, fever, dehydration, heart disease, mental illness, poor circulation, sunburn, and prescription drug and alcohol use," the CDC says, adding that older people — specifically those 65 and older — are at high-risk for heat-related illness.

There are things you can do to stay safe, according to The Federal Emergency Management Agency's Ready program.

First, be prepared:

• Do not rely on a fan as your main cooling device. They create airflow and might keep you comfortable, but they do not reduce your body temperature — a key part of preventing heat-related illness.
• Stay in the air conditioning. If your power is out, identify places in the community you can go, such as libraries, malls or cooling centers.
• Cover windows with drapes or shades.
• Weather-strip doors and windows.
• If you are struggling to afford cooling costs or weatherization, the Low Income Home Energy Assistance Program could help.

During extreme heat, remember:

• Drink plenty of fluids even if you don’t feel thirsty, the CDC says.
• You should limit your activity outdoors, but if you do go out, wear loose, lightweight and light-colored clothing.
• A cool shower or bath can help you cool down.
• Try to avoid using your oven or any other household appliances that could heat up your house.
• Check on friends and neighbors — especially those in high-risk groups.
• Watch for the signs of heat stroke. These can include red, hot and dry skin with no sweat. Also looks for a rapid, strong pulse and dizziness or confusion, the CDC says.

What to do if you see signs of heat stroke? Here's advice from the CDC:

If you see any of these signs, you may be dealing with a life-threatening emergency — you should get medical attention as soon as possible, the CDC says. While waiting for first responders, try to cool the person down.

• Get them out of the sun.
• Lower their body temperature by putting them in a tub or shower with cool water. You can also wrap the person in a wet sheet and fan them if the humidity is low, according to the CDC.

As of Tuesday morning, all visitors are out of Yellowstone National Park, Superintendent Cam Sholly said at a news conference. He said officials have also located all backcountry campers, with only one group left in the northern loop.

The Yellowstone River, which runs through the park and several Park County cities, swelled to a record high Monday due to recent heavy rainfall and significant runoff from melting snow in higher elevations, the park has reported.

Officials say the park will remain closed to visitors. The flooding has also prompted park evacuations and left some in surrounding communities trapped without safe drinking water.

The next step is to evaluate the infrastructure, but Sholly said there is not a firm timeline on when the park will be able to reopen.

When asked about the extent of the damage, he said, "We don't know exactly yet," adding that the northern loop was most affected by the flooding.

When the flood waters subside next week, Sholly said the park will pull together people from different agencies to assess and calculate how much time and money it will cost to rebuild. The superintendent said this is going to be a big job, estimating there are "hundreds" of bridges and major roads throughout the park that need to be evaluated.

Unprecedented flooding: The Yellowstone River reached record-high levels Monday in the Montana towns of Corwin Springs and Livingston.

At Corwin Springs, the river rose more than 5 feet on Monday morning, according to the National Oceanic and Atmospheric Administration river gauge data. The gauge reading was 13.85 feet on Monday afternoon, surpassing the historical high crest of 11.5 feet from 1918.

The river gauge reading at Livingston was a record 10.9 feet.

June precipitation has been more than 400% of average across northwestern Wyoming and southern Montana, according to CNN meteorologists.

CNN's Claudia Dominguez and Sara Smart contributed to this reporting.

A Montana helicopter company has flown dozens of people in and out of the Gardiner community airstrip in Park County on Monday and Tuesday after the town located at the northern entrance to Yellowstone National Park was isolated by heavy flooding in the area.

Laura Jones with Rocky Mountain Rotors told CNN that the company’s aircraft has transported about 40 people.

“We haven't ‘rescued’ anyone that was in danger, we have mainly been transporting people out of there (since there was no way out) to catch their flights home,” Jones said in an email. “We have also taken some passengers in who had pets they needed to get to or live there and needed to get home.”

She said they learned on Tuesday afternoon that the road from Gardiner to Livingston had opened and people had gotten out.

“We have had several flights we had booked tomorrow, and Thursday cancel now that they can get out,” she said.

Hundreds of thousands of customers continue to be without power today after severe storms impacted several states on Monday in the Midwest and the Ohio River Valley. 

On Tuesday, another round of severe weather is adding to the totals without power, this time in the Southeast.

All of these regions have now been under a heat advisory and/or excessive heat warning for a second day, with temperatures climbing into the upper 90’s and heat indices making it feel above 100 degrees.

Currently, there are 490,143 customers without power in at least seven states, according to data from PowerOutage.US. 

Ohio continues to experience the brunt of the outages at 310,324 customers in the dark.

Here's a look at the outages:

• Ohio — 310,324
• West Virginia — 56,986
• Indiana — 48,910
• Michigan — 21,208
• Illinois — 21,006
• Georgia — 17,413
• Wisconsin — 14,296

There are currently 40 active large wildfires burning in the United States, according to a fire update from the National Interagency Fire Center (NIFC).

So far, the 40 large fires have burned approximately 1,192,672 acres in six states, the NIFC said. 

“Seven new large fires were reported yesterday, three in Alaska and Arizona and one in Utah. More than 6,200 wildland firefighters and support personnel are assigned to incidents,” according to the NIFC. 

The majority of the fires this year have been due to human-related causes.

“Nearly 96% of the wildfires reported this year were caused by people," the NIFC said. "States with the most human-caused wildfires include: Texas, North Carolina, California, Georgia and Florida.”

Nearly 30,000 wildfires have burned around 2.5 million acres across the US so far this year — exceeding the pace of any year over the past decade, statistics released Tuesday by the National Interagency Fire Center show.

This makes 2022’s early wildfire season the largest in a decade, and the third-largest since records began in 1999 — behind a record 4 million acres in June in 2011, and 2.7 million acres burned in 2006, according to NIFC spokesperson Sheri Ascherfeld.

Alaska is currently experiencing the most active wildfires in the country.

In an update today from the Alaska Wildland Fire Information, it said the East Fork Fire has burned 129,197 acres and the Apoon Pass Fire has burned 43,820 acres.

These are the states currently reporting large fires, according to NIFC:

• Alaska (23)
• New Mexico (6)
• Arizona (6)
• California (3)
• Texas (1)
• Utah (1)

CNN's Ella Nilsen and Brandon Miller contributed reporting to this post.

Over three days, abundant rainfall and rapid snowmelt combined to produce up to three-quarters of a foot of water runoff, leading to the historic flooding across the region that spans Yellowstone National Park and the Montana and Wyoming border.

"The Beartooths and Absarokas received anywhere from 0.8 inches to over 5 inches of rainfall over the course of June 10th through June 13th," the National Weather Service in Billings revealed Tuesday.

"This combined with anywhere from 2 to nearly 5 inches of snow melt equivalent, leading to a total water event of at least 4 to 9 inches," they added. Snow melt equivalent is the measurement of water created once the snow melts.

According to CNN Weather calculations, this amount of runoff is similar to the area receiving two to three months of June precipitation in only three days.

Though cooler temperatures and drier weather have allowed for the rivers to drop back to normal levels, even hotter temperatures are expected late this week and weekend, which could bring additional flooding to the region.

“Plan on highs in the 60 to 70s in the higher elevations [Friday and Saturday], which should melt much of the remaining snowpack and lead to additional river rises,” the NWS in Billings said on Tuesday.

This week’s extreme weather — severe flooding, dangerous heat and associated power outages — spans thousands of miles, but they are connected by one thing: a massive pattern of blocked weather over the US.

These “blocking systems” disrupt the normal movements of weather systems, and can keep heat trapped in one part of the country. Atmospheric blocking happens when the fluctuation of the jet stream — the narrow bands of powerful winds high in the sky that determine day-to-day weather around the globe — causes a traffic jam of sorts.

During the summer, these traffic jams can cause extreme and prolonged heat, also known as “heat domes.” This happened during the deadly heat wave that seared the Pacific Northwest last year, according to a recent study published in April.

Studies have shown that the climate crisis could affect the frequency of blocking, in concert with its geographic distribution. But scientists say one thing is certain: climate change is making heat waves warmer and severe storms such as hurricanes wetter than previously recorded.

The town of Gardiner in Park County, Montana, has been left isolated and surrounded by water after heavy flooding washed out bridges and roads, Park County officials said in a post on their Facebook page on Tuesday.

“Extensive flooding throughout Park County has washed out bridges, roads, and left communities and homes isolated,” the post said. “Gardiner is currently isolated and surrounded by water.”

Gardiner is located at the northern entrance to Yellowstone Park, according to its website.

“Gardiner is a center of activity for visitors to the region, serving as the only entrance into Yellowstone National Park that remains open to wheeled-vehicle use year-round,” according to the town’s website.

CNN tried to contact Park County officials, to confirm how many people are affected but has been unable to reach anyone.

The town is also urging visitors to be patient because after the flood waters recede "we could be looking at a significant loss to our tourism based economy," Gardiner's tourist information center said in a Facebook post.

"We ask for you to be patient before cancelling your plans, and especially in asking for a return on your deposits as our hard working small businesses look at the potential prospects of terrible economic hardship this summer," the post said.

The flooding has caused many roads and bridges to be inaccessible. Some railroad tracks have had to shut down because water have crossed the tracks, the post said adding that the “majority of bridges crossing the Yellowstone River in the Paradise Valley are not safe for use. Exceptions are Pine Creek, Murphy Lane and Mill Creek, but they are available for emergency traffic only.“

The Yellowstone River runs through the town of Gardiner.

“Personnel from agencies across the region and state are assisting local resources on the response. There are evacuations and rescues going on throughout the county, including two air lifts (up the Boulder and near Cooke City-Silver Gate) and several swift water rescues,” the post added.

“Two Bear Air and the National Guard have been assisting with the air rescues while Park County Search is assisting with the swift water rescue,” the post said, adding that rescue personnel has been brought in to deal with “potential need.” 

Officials warned residents that displaced wildlife could traverse their properties and that bears, deer and domestic livestock have been spotted.  

The flooding, officials say, “has also made drinking water unsafe in many areas” and the Montana Department of Environmental Quality issued a no drink order in the area after a water main broke.

Officials also said that once waters recede bridges and roads will be assessed to verify if they are structurally sound.

See video of the devastation in Gardiner here.

The Tennessee Valley Authority is seeing a record demand for power demand this month, according to a company tweet Tuesday.