A massive heat dome is gripping much of the US again this week, with the Midwest facing a brutal combination of scorching temperatures and stifling humidity due in part to so-called «corn sweat,» or the extra moisture crops release into the air. This added humidity is pushing heat indexes well above 100 degrees across parts of the Corn Belt and beyond, compounding the risks for millions under excessive heat warnings and advisories.

The extreme heat bearing down across the US this summer can have a serious impact on public health. Excess heat can exacerbate common health conditions, but it can also mess with your air conditioning, overheat phones and cause meltdowns for other tech. If you live in an area at risk for extreme heat, or know someone who does, you can sign up for a free alert system to help you prepare. The HeatRisk tool from the National Weather Service can send personalized warnings straight to your inbox, giving you advance notice when dangerously high temperatures are headed your way.

HeatRisk is free to use and you’ll want to keep tabs on it to avoid heat safety issues, such as heatstroke, dehydration or fatigue. Here’s how to use it and why you should. 

Read more: This CDC Tool Can Help You Track Heat Risks on Trips and in Your Area

What is NWS HeatRisk?

NWS HeatRisk is a clickable map of the US, which is used to forecast extreme heat and assess the impact of that weather on public health. You can click anywhere on the interactive map and pull up a seven-day forecast of risk assessments for any city, town or area. 

The threat assessment is built on a five-level system that’s color-coded for severity, with green representing little to no risk and magenta representing the highest risk. The map will display a seven-day forecast for anywhere in the country, along with the color of the health threat level.

The system also considers how unusual the heat is for your area, how long the heat is expected to last and how it could affect people who are more vulnerable, such as older adults, kids or outdoor workers.

Read more: Super Common Health Conditions Can Make a Heat Wave More Dangerous: Here’s How to Prepare

Threat colors

NWS HeatRisk has five levels, each with a different color that corresponds to the size of the health risk:

0: Green

According to the NWS tool, there’s little to no risk involved with the forecasted heat at the green level.

1: Yellow

At the yellow level, there’s a minor risk for people who are extremely sensitive to heat.

2: Orange

The orange level represents a moderate risk to the general public, with potential danger to health systems and heat-sensitive industries.

3: Red

Red means there’s a major risk to anyone without access to immediate cooling and hydration, with likely impacts to health systems and heat-sensitive industries.

4: Magenta

The most extreme level is magenta. It’s both a rare occurrence and one that’s of long duration, with no overnight relief and is likely to affect health systems, heat-sensitive industries and infrastructure.

How to sign up for heat risk alerts 

To get free heat warnings, go to Heat.gov, enter your ZIP code and sign up for email or text alerts. You’ll get daily updates when your area faces extreme heat levels that could pose a health risk. 

Signing up for alerts is a quick step that could help you plan ahead, from adjusting outdoor activities to checking on family or neighbors, or just opting to stay hydrated and inside.

Other ways to track heat risks

Similar to NWS HeatRisk, a tool from the US Centers for Disease Control and Prevention called the HeatRisk Dashboard gives you a seven-day forecast to assess the potential health impact from extreme heat. 

Data Explorer is another tool from the CDC’s Environmental Public Health Tracking Program, which offers further HeatRisk information and assessment resources for COVID-19 and other illnesses.

Read more: Here’s How to Keep Your Kitchen Cool (and Lower Your Energy Bill) During a Heat Wave

Why extreme heat warnings matter 

Summer 2025 has already been a scorcher in many parts of the country. It’s important to stay diligent since extreme heat is the deadliest weather hazard in the US, causing more deaths each year than hurricanes, floods or tornadoes. 

The risks of heat are only growing. Heat waves are lasting longer, nighttime temperatures are staying high and unusual humidity — like the current «corn sweat» in the Midwest — can make it even harder for your body to cool down.

Staying informed is one of the easiest ways to protect yourself and your loved ones. Along with signing up for alerts, the CDC recommends learning the signs of heat-related illnesses, drinking plenty of water and never leaving children or pets in cars.

For more ways to stay safe this summer, check out CNET’s guide to the best portable AC units, tips for cooling down this summer and how to make your home more heat-resilient.