‘Heat dome’ to bring scorching temps to most of US

LOS ANGELES - Another dangerous heat wave is set to deliver sweltering weather next week to most of the lower 48 states, placing areas once again under extreme drought conditions and in jeopardy of breaking more records.

Millions of Americans will be under excessive heat warnings and advisories next week, with parts of Kansas and Missouri already under said warnings and advisories in place for sections of the Midwest and Southeast. 

The National Weather Service says a key point of the upcoming heat wave will be the humidity in the Southeast and Mississippi Valley. 

"Although the actual temperatures are not expected to be that unusual for this time of year for these areas, humidity levels are expected to be high, resulting in hazardous heat index values," Scott Handel, a lead meteorologist with the NWS, told FOX Television Stations.

While above-normal temperatures are not surprising to meteorologists, trends over the past 15 years have supported increased heat across much of the country and drier-than-normal soil moisture is also contributing to the dangerous heat.

"The Climate Prediction Center seasonal outlooks issued earlier this year favored above-normal temperatures for most of the country for this summer and what we are currently observing is consistent with these outlooks," Handel said.

What is a heat dome?

According to the NWS, the pattern behind the stretch of oppressive heat is associated with a strong upper-level ridge of high pressure. 

A "heat dome" is an expansive area of high pressure in the atmosphere that causes air to sink and compress over large areas of the country. As this air is compressed, the temperature increases which can result in heat waves. 

This type of event is already occurring across parts of the country and is expected to expand next week.

How hot will it get?

Early estimates indicate that most of the contiguous United States will see highs running 10 to 15 degrees above average. 

When you factor in the humidity, it’ll feel like it’s well into the triple digits for millions (even if areas don’t hit triple-digit numbers). 

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The pattern could also spark severe thunderstorms and cause gusty winds. 

Heat will continue to bring triple-digit temperatures to many areas, and officials are sounding the alarm to take additional precautions if necessary to stay safe and hydrated.

Which states will experience heat wave?

The heat wave is expected to affect much of the contiguous United States, including much of the Southeast, Mississippi Valley, Northern and Central Plains, Northern Rockies, and interior parts of the Northwest. 

The states with the greatest chances of impacts include Georgia, South Carolina, North Carolina, Virginia, Kentucky, Tennessee, Alabama, Mississippi, Arkansas, Iowa, Missouri, South Dakota, Nebraska, Kansas, Oklahoma and Louisiana. 

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"Humidity will play a larger role with this heatwave, with probabilities exceeding 40% for heat indices exceeding 105 and even potentially 110 F across the Lower and Middle Mississippi Valley and Southeast," the NWS said. 

How long will the heat wave last?

Temperatures are already climbing and a heat wave is already ongoing across parts of the country, particularly across the Northern Plains and parts of the interior West. 

This heat wave is set to expand eastward next week to the Mississippi Valley and Southeast. Thereafter, an elevated risk of excessive heat is expected to persist for many of these areas through next weekend and into the following week.

Heat safety tips

The National Weather Service is cautioning those impacted by the heat wave to stay in air-conditioned buildings if possible.

"Anytime excessive heat is possible during the peak summer season is a cause for concern from a health perspective," Handel said. "Vulnerable populations (young children, the elderly, people with medical conditions, and pregnant women) can suffer from heat stroke, severe dehydration and trouble with breathing due to a greater likelihood of poor air quality." 

Emergency physicians say heatstroke, more severe than heat exhaustion, will present with sickness, weakness and inability to walk.

"If they feel they're getting illness related to too much heat, we'd rather they come in early and have it be a false alarm because that's when we have the opportunity to treat," said Dr. Ronn Berrol, emergency director of Summit/Alta Bates.

It’s important to limit outdoor activity during the hottest part of the day — the afternoon hours. The NWS also suggests checking in with at-risk friends, family and neighbors.

Lastly, make sure to drink water before, during and after working or exercising outside. 

Extreme drought conditions persist

The combination of the heat, low humidity and wind gusts have increased the threat of wildfires in the West. According to the U.S. Drought Monitor, exceptional and extreme drought persists in the West.

A robust monsoon circulation provided limited Southwestern drought relief, particularly in parts of Arizona, New Mexico, and southwestern Colorado. Farther north and west, however, little or no rain fell in California, the Great Basin, and the Northwest, where dozens of wildfires were in various stages of containment.

More than half of the US west is suffering exceptional or extreme drought – the highest rating since authorities began monitoring the phenomenon 20 years ago.

Thirteen new large fires were reported Thursday, bringing the national total to 83 large fires and complexes that have burned 1,366,587 acres. Almost 22,000 wildland firefighters and support personnel are assigned to incidents across the country.

This story was reported from Los Angeles.