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We’ve all heard the term “severe weather” or “severe thunderstorm,” but what actually defines these categories? Here is a quick guide to understanding these terms and the five categories of severe weather risks.

What is it that makes a storm severe?

According to the National Weather Service (NWS) in order for a storm to be categorized as severe it needs to produce one or more of the following elements:

  • Wind speeds of 58 miles per hour or greater.
  • Hail 1″ in diameter or larger.
  • A tornado.

The 5 severe weather risk categories

A division of the NWS called the Storm Prediction Center (SPC) assesses the risk of severe weather and places them into 5 different category ratings from 1 to 5, with 5 being the highest.

The 5 categories are: Marginal, slight, enhanced, moderate and high. Let’s look at the qualifications for each category.

1. Marginal risk

Defined as: Isolated severe storms.

Possibilities: Heavy rain, winds, and hail are the main threats. Isolated severe storms are possible.

Hazards: Wins 40-60 mph, up to 1″ hail, low tornado risk.

Scope: Limited in duration, coverage, and intensity.

2. Slight risk

Defined as: Scattered severe storms.

Possibilities: Damaging winds and hail are typically the main threats. Scattered severe storms are possible. Low threat of isolated tornadoes.

Hazards: Damaging winds, 1″-2″ hail, 1-2 tornadoes.

Scope: Not widespread, isolated intense storms, short-lived.

3. Enhanced risk

Defined as: Numerous severe storms.

Possibilities: Significant wind damage, large hail, and a few isolated tornadoes are the main threats. Numerous severe storms are possible.

Hazards: Likely wind damage, 1″-2″ hail, several tornadoes.

Scope: Widespread with a few intense storms, more persistent.

4. Moderate risk

Defined as: Widespread severe storms.

Possibilities: Widespread wind damage, significant hail damage, and several strong tornadoes are the typical main threats.

Hazards: Widespread wind damage, destructive hail, strong tornadoes.

Scope: Widespread severe storms and long-lived-intense storms.

5. High risk

Defined as: Widespread and long-lived destructive storms.

Possibilities: Damaging winds, major structure from large hail, and strong tornadoes are typically the main threats. Strong, destructive storms of a long-duration are possible.

Hazards: Catastrophic hail, tornado outbreak, Derecho.

Scope: Widespread, long-lived, destructive storms.

Keeping safe in severe weather

Severe weather brings a variety of dangers both indoors and outdoors. If you live in an area that frequently has severe weather, it’s important to own a weather radio, either battery-powered or handcrank, in order to be able to receive weather updates and warnings should the power go out.

Outdoor threats

If you are outside during severe weather, get indoors as quickly as possible.

Tornadoes and strong straight-line winds can send projectiles flying, uproot trees, and take down power lines.

Large hail could strike you and cause injuries, including knocking you unconscious.

You can also be struck by lightning.

Indoor threats

When severe weather brings strong winds or tornadoes it’s important to stay away from windows to protect yourself from flying debris.

In the case of a tornado, get to your storm shelter, basement, or the lowest level of your residence. If you have none of these available, get to an interior room without windows, often this is a bathroom.

If you are sheltering in a bathroom, get inside the tub, lay down, and place protective padding over the top of you. In any case, the goal is to put as many walls between you and the outside as possible.

Additionally, cover your head with a hard object if available, otherwise, use a pillow and/or blanket to protect yourself from flying debris.