What Are Thunderstorms?

A thunderstorm comes from rain-bearing clouds that also produce thunder and lightning. All thunderstorms produce lighting and therefore are dangerous. A thunderstorm is classified as a severe thunderstorm when it contains large (at least one inch) hail and/or winds of 58 MPH or greater. If you can hear thunder, you are close enough to be affected by lightning, which can strike up to 10 miles ahead of or trailing a storm. Thunderstorms can occur by themselves, in clusters, or in lines. The typical thunderstorm is 15 miles in diameter and produces heavy rain for 30 minutes to an hour.

Why Prepare?

Thunderstorms are very common in the spring and summer months throughout Massachusetts, with 10–30 days of thunderstorms each year. Thunderstorms can be extremely destructive and can produce lightning, hail, high winds, flash floods, or tornadoes.


The National Weather Service issues severe thunderstorm watches and warnings to alert the public of potential severe weather. It is important to understand the difference between watch and warning so you know what to do to stay safe:

Severe Thunderstorm Watch

Thunderstorms are possible based on weather conditions.

        • Pay attention to changing weather conditions, and be prepared to shelter immediately.

Severe Thunderstorm Warning

A severe thunderstorm has been sighted or indicated by weather radar.

        • Seek shelter immediately.

Before a Thunderstorm

  • Be informed by receiving alerts, warnings, and public safety information before, during, and after emergencies. Download the Massachusetts Alerts app.
  • Create and review your family emergency plan.
  • Assemble an emergency kit.
  • Make a record of your personal property by taking photos or videos of your belongings. Store these records in a safe place.
  • Prepare your home.
    • Remove dead or rotting trees and branches around your home that could fall and cause injury or damage.
    • Clear clogged rain gutters to allow water to flow away from your home.

During a Thunderstorm Watch

  • Listen to the National Oceanic and Atmospheric Administration (NOAA) Weather Radio or to a local news station for the latest information.
  • Follow instructions given by public safety officials.
  • Be alert to changing weather conditions and be prepared to take shelter immediately.
  • Consider postponing outdoor activities.
  • Secure or bring in outdoor objects (patio furniture, children's toys, trash cans, etc.) that could be blown away or cause damage during strong winds.
  • Consider unplugging sensitive electronic equipment before the storm.

During a Thunderstorm

When you first hear thunder, see dark threatening clouds developing, see lightning, or after a severe thunderstorm warning is issued, take actions to stay safe. Remember “When Thunder Roars, Go Indoors!” If possible, monitor local media for the latest information and follow the instructions given by public safety officials.

If You Are Outside

  • Go indoors immediately. If you cannot get inside, take shelter in a vehicle.
  • If you are in an open area, go to a low place such as a ravine or valley and watch out for flash flooding.
  • If you are in a forest, seek shelter in a low area under a growth of small trees.
  • If you are boating or swimming, get to land and seek shelter immediately.

If You Are in a Car

  • Stay in your car if you are on the road. If driving conditions worsen, find a safe place to pull over and park.
  • Avoid touching metal or other surfaces in and on your vehicle.

If You Are Inside a Building

  • Stay away from windows and doors. Strong thunderstorms can cause flying debris that could do significant damage.
  • Avoid using a corded telephone, except for emergencies. Cordless or cellular telephones are safe to use. Unplug appliances, air conditioners, and other electrical items like computers to avoid damage from a power surge.
  • Avoid showering, bathing, washing dishes, or doing laundry. Plumbing and bathroom fixtures can conduct electricity.
  • Avoid contact with metal objects (yard equipment, motorcycles, bicycles, etc.).
  • Stay inside until at least 30 minutes after you last hear thunder or see lightning.

After a Thunderstorm

  • Continue to monitor media for emergency information.
  • Follow instructions from public safety officials.
  • Call 9-1-1 to report emergencies including downed power lines and gas leaks.
  • Call 2-1-1 to obtain shelter locations and other disaster information.
  • Stay away from downed utility wires. Always assume a downed power line is live.
  • Stay out of damaged buildings and areas until authorities deem them safe.
  • Check your home for damage:
    • If you believe there is a gas leak, go outdoors immediately, and do not turn electrical switches or appliances on or off.
    • If your home or property is damaged, take photos or videos to document your damage, and contact your insurance company.
  • If your power is out, follow our power outage safety tips.
    • Report power outages to your utility company.
    • Use generators and grills outside because their fumes contain carbon monoxide. Make sure your carbon monoxide detectors are working as it is a silent, odorless, killer.
  • If phone lines are down, use social media or texting to let others know you are OK.
  • Remember “Turn Around, Don’t Drown!” Don’t drive through flooded roads. Cars can be swept away in just two feet of moving water.