A Major Heat Wave Is Coming: Here’s What You Need to Know

Get ready, New England — the weather is about to turn dangerously hot over the next several days. A massive "heat dome" is building across the country, and by the time we reach the Fourth of July, temperatures in parts of Massachusetts could soar well into the 90s and even hit 100°F or higher. Let’s break down exactly what’s happening, day by day, and how to stay safe.

Monday and Tuesday: Enjoy the Nice Weather While It Lastes

The first couple of days of this forecast are actually pretty pleasant — so soak them up!

• Monday already brought comfortable conditions, and Tuesday looks even better.
• Expect plenty of sunshine across the region.
• Temperatures will range from the 70s along the coast to the upper 80s inland — a classic, comfortable summer day.
• Morning temperatures will start in the 60s, with moderate (not too sticky) humidity.
• Sea breezes along the coastline Tuesday afternoon may keep some spots near the beach in the 70s, so temperatures can vary a lot depending on how close you are to the water.

Important Point

Tuesday is the most comfortable day of the next five days. If you have any outdoor plans — yard work, exercise, errands — Tuesday is your best bet!

Tuesday’s Forecast by Area

Wednesday: The Heat Arrives — And It’s Serious

Things change dramatically starting Wednesday. Here’s what happens:

1. Tuesday night into early Wednesday: A warm front moves in. Temperatures will stay in the 60s to near 70°F, and humidity will still feel tolerable when you wake up.
2. Late morning to early afternoon Wednesday: The humidity will surge. Dew points (a measure of how much moisture is in the air — think of it as how "muggy" it feels) will jump into the lower 70s. The air will start to feel completely tropical.
3. Temperatures will climb into the lower to mid-90s°F.

An Extreme Heat Watch Has Been Issued

The National Weather Service has issued an Extreme Heat Watch from Wednesday morning through Saturday (the Fourth of July) for all of Massachusetts and the rest of New England — except Cape Cod and the Berkshires.

• Early Wednesday morning (just after sunrise) is still okay to be outside.
• By Wednesday afternoon and evening, it will be intolerable for any strenuous outdoor work or activity.
• The "feels like" temperature (called the heat index) on Wednesday could hit a scorching 109°F in parts of New England.

What Is the Heat Index?

The heat index is what the temperature actually feels like to your body when you combine the real air temperature with humidity. When it’s humid, your sweat can’t evaporate as easily, so your body can’t cool itself down. That’s why 95°F with high humidity can feel like 109°F — and why it’s so dangerous.

Thursday Through the Weekend: Record-Breaking Heat

The heat doesn’t let up — it gets even worse.

• Dew points are forecast to reach the mid- to upper 70s°F on Thursday.
• That means heat index values of 105 to 110°F.
• Actual air temperatures could hit 102°F or higher in the Boston area.
• The record high for July 4th in Boston is 98°F — and forecasters say we could break that record.

A Look at the Record Books

• The last time the Boston area hit triple digits (100°F+) was June 24, 2025, when it reached 102°F.
• The all-time highest temperature ever recorded in Boston was set on July 4, 1911.
• High-temperature records are being broken far more often than cold-temperature records these days, which is consistent with the long-term pattern of climate change.

What’s Causing This? Meet the "Heat Dome"

This heat wave isn’t random. It’s being driven by a massive high-pressure system — commonly called a "heat dome" — that stretches from the middle of the United States all the way to the East Coast.

What Is a Heat Dome?

Imagine a giant invisible lid sitting over a huge part of the country. That’s basically what a heat dome is. High pressure pushes air downward, and as that air sinks, it warms up. When the high-pressure system gets stuck in place (like a pot with a lid on it), the air keeps getting hotter and hotter day after day. That’s exactly what’s happening this week.

The dark brown areas on the weather maps show where temperatures will soar into the 100s°F — covering a big chunk of the U.S. this holiday week.

How to Stay Safe in Extreme Heat

Here’s what you need to do to protect yourself and your family:

• Get outdoor activities done early in the morning. The sun rises before 5:15 a.m., so you have a few hours before 8 or 9 a.m. when the heat is still manageable.
• Avoid strenuous outdoor work from Wednesday afternoon through Saturday.
• Wear sunscreen if you’re heading to the beach — the sun is incredibly strong right now.
• Stay hydrated. Drink plenty of water, even if you don’t feel thirsty.
• Check on elderly neighbors and relatives, young children, and pets — they’re especially vulnerable to heat.
• Never leave children or pets in a parked car, even for a minute.
• Spend time in air-conditioned spaces during the hottest parts of the day. The beach will be the best natural escape, but indoor spaces with air conditioning are ideal.

Summary

The bottom line: A significant, dangerous heat wave is heading for New England this week. Tuesday is your last comfortable day. By Wednesday afternoon, the heat becomes extreme and potentially life-threatening. Plan accordingly, stay cool, and take this seriously.

Frequently Asked Questions

Q: What’s the difference between temperature and heat index?
The temperature is what the air actually measures on a thermometer. The heat index is what it feels like when you factor in humidity. High humidity makes it harder for your body to cool off through sweating, so the heat index is often higher than the actual temperature — and that’s what makes it dangerous.

Q: Who is most at risk during extreme heat?
Older adults, young children, people with chronic health conditions, and pets are at the highest risk. People who work outdoors should also take extreme caution and limit activity to early morning hours.

Q: Why is the heat wave lasting so many days?
A "heat dome" — a large, stuck area of high pressure — is trapping hot air over the region. Because the high-pressure system isn’t moving, the heat builds day after day. It will continue until the pattern breaks.

Q: Could temperature records actually be broken this week?
Yes. The forecast calls for temperatures around 102°F on July 4th, which would break the daily record of 98°F for that date. The Boston area has been setting far more high-temperature records than low-temperature records in recent years, consistent with climate trends.

Q: Is the beach a good place to be during this heat wave?
The beach is one of the best places to be thanks to sea breezes that keep temperatures cooler near the water. However, the sun is extremely strong, so wear sunscreen, stay hydrated, and still avoid being out during the peak afternoon hours if possible.