A heat wave has been hovering over the Midwest and the eastern US this week, and the National Weather Service expects that to continue for much of the country for the upcoming holiday weekend. 

Over 175 million Americans across the Midwest and East are at risk of heat-related issues based on The Weather Channel's HeatRisk tracker. Extreme heat advisories have also been issued for the Central Plains, South and Northeast regions. Thermometers will hit triple digits in many areas, and some locales will exceed 110 degrees. Overnight temperatures could hover around 80 degrees. 

That means there will be no relief even at hours when the sun isn't at its strongest.

"Heat is referred to as a 'silent killer' because it does not have the sudden, dramatic visual impacts of other extreme weather events," Jessica Lee, services coordinator at NOAA's Weather Prediction Center, said in an email to CNET. "Unlike a tornado or a hurricane, a heat wave does not leave behind a visible path of destruction. This leads to heat often being seen as a mere nuisance and not as a deadly threat, leading to a lack of urgency in response."

As temperatures rise this week, it's crucial to stay safe and be alert to all weather advisories. If you have underlying health conditions, the heat can worsen them if you aren't careful. This may mean staying in and changing your plans or taking extra precautions if you have no choice but to be outside. In extreme heat situations, listening to the experts on how to protect yourself can be a matter of life and death.

Temperatures in London reached 36.4 degrees Celsius, or more than 97 degrees Fahrenheit, as Europe dealt with a deadly heat wave in June. High temperatures are expected for the eastern and central US this week.

Dan Kitwood/Getty Images

Keep an eye on the heat

The Centers for Disease Control and Prevention has a HeatRisk tracking tool that gives you the daily risk level based on your ZIP code, plus tips to help manage your health in the heat. Pay attention to your weather app for temperatures and weather alerts. You may also see a feels-like temperature, which can be higher than the thermometer temperature because of humidity and other factors.  

"Because the Heat Index is calculated for shady areas, it does not fully account for the potential heat stress in direct sunlight and can underestimate the heat's effect on your body by up to 15 degrees Fahrenheit," Lee said.

During heat waves, you may expect temperatures to cool at night, but sometimes they don't drop enough to offer genuine relief. Cooler night temperatures give your body a chance to reset from the heat. But when temperatures remain high, your body doesn't have that chance, which can be dangerous for your health. So even when the sun goes down, continue to pay attention to how hot it is -- and not just outside your home.

Make sure your home is cool 

Keeping your home cool during a heat wave is essential to protecting your health and that of your loved ones and your pets. 

"Stay in the coolest area of your home as much as possible," said CNET Editor Corin Cesaric-Epple. Staying inside can also protect you against sunburns, which, aside from being painful, make it harder for you to stay cool.

In your home, air conditioning is the best way to ensure you stay comfortable and safe.

Cesaric-Epple and CNET's Labs team have reviewed more than a dozen portable and window AC units and found that, of the two types of non-central air conditioning, window units have optimal cooling performance. Energy Star models can also keep you cool while using less electricity.

If you're not in the market for a new AC unit, there are other tips to keep your home cool. Consider keeping your curtains closed to prevent sunlight from warming your home. And use weatherstripping or other materials to seal up any gaps around your doors and windows to keep cool air in and hot, humid air out. 

Stay hydrated 

It's especially important to stay hydrated during heat waves. Dehydration can be dangerous because your body needs sweat to stay cool. Drink water regularly and take water with you when you go outside. The CDC recommends drinking eight ounces of water every 15 to 20 minutes when working outside in the heat. You should drink in short intervals instead of consuming a large amount all at once. And don't overdo it: The CDC doesn't recommend drinking more than 48 ounces of water per hour. 

CNET has more advice to help you stay cool this weekend, and throughout the summer, including a handheld fan we recommend to help you stay cool, and heat illness signs to watch out for.