Severe thunderstorm watch or warning: when wind and hail mean shelter

The severe threshold

Wind and hail can be the main threat

The National Weather Service classifies a thunderstorm as severe when it can produce wind of at least 58 mph, hail at least 1 inch in diameter, or a tornado. Lightning and heavy rain can still be dangerous below those severe-weather thresholds.

• Straight-line wind can bring down trees and power lines, turn loose objects into projectiles, and damage roofs and buildings.
• Large hail can break windows, injure people and animals outdoors, and damage vehicles and roofs.
• A tornado warning is a separate alert. A severe thunderstorm warning does not mean a tornado is impossible, so keep checking updates until the threat has passed.

The August 11, 2026 derecho across northern Illinois and northwestern Indiana is a recent official example of the danger: the NWS documented widespread 70 to 100-plus mph straight-line winds, including a 99 mph gust at Gary/Chicago International Airport. This is historical context, not a current alert.

Use the exact product name

Outlooks, forecasts, watches, and warnings answer different questions

Always read the official product title, issue time, valid period, affected area, hazards, and instructions. A broad risk on an outlook does not mean every location will see severe weather, and it is not a local warning.

SPC Convective Outlook

An outlook shows where organized severe thunderstorms may occur over the next one to eight days. Its risk categories communicate probability and coverage across broad areas; they do not predict a storm at one address.

Local forecast

A forecast describes expected timing and conditions for a place. It supports planning, but it is not itself a watch or warning and may change as new observations arrive.

Severe Thunderstorm Watch

A watch means severe thunderstorms are possible in and near a broad area. Review where you will shelter, secure loose items, and be ready to receive warnings.

Severe Thunderstorm Warning

A warning means a severe thunderstorm is occurring or imminent in the warned area. Move inside a sturdy building, go to an interior room, and stay away from windows.

Warning damage tags

Base, considerable, and destructive describe increasing impact

NWS Severe Thunderstorm Warnings may include a damage-threat tag. The tag supplements the warning; it does not replace the need to shelter when your location is inside the warning polygon.

When a warning includes you

Get inside, move inward, and protect yourself from glass

1. Enter a substantial building; a hard-topped vehicle is safer than remaining outdoors, but a sturdy building is better.
2. Move to an interior room on the lowest practical floor and stay away from windows, skylights, and exterior doors.
3. Keep shoes on and protect your head from broken glass and falling debris.
4. Bring people and pets inside. Do not step outdoors to photograph hail or inspect damage while the warning is active.
5. Continue monitoring official alerts in case a tornado or flash-flood warning is issued.

If you live in a mobile or manufactured home, identify a nearby sturdy shelter before storms develop and allow time to reach it during the watch stage. Do not wait for damaging wind to begin before following that plan.

After the storm

Wait for the warning to expire, then watch for secondary hazards

• Stay away from downed power lines and anything touching them.
• Do not enter a visibly damaged building until authorities say it is safe.
• Never drive through floodwater or around a road barricade.
• Use generators only outdoors and well away from doors, windows, and vents.
• Keep checking official alerts; another storm may follow the first one.