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What Do the Forecasted Weather Classes Mean?

PSAI weather forecasts show three days of events: today, tomorrow, and the day after tomorrow. Each weather forecast is tagged with a color-coded storm class indicator ranging from 1 (low) to 5 (high). Learn more about these storm classes and how to interpret them below.

Definition of Severe Weather

Severe weather in the United States is defined as 1" or greater hail, 58mph or greater winds, and/or a tornado. Please keep in mind that all severe weather events, regardless of class, represent expected areas based on the current forecasts, which can change.

Storm Classes Represent Coverage, Not Severity

In general, it's important to understand that the weather classes represent the expected coverage of severe weather within the specified timeframe and geographic area—not necessarily weather event severity. 

In other words, a higher class means more of that area is expected to see severe weather, but it does not necessarily mean that the weather event itself will be more severe. To illustrate this point, there could absolutely be significant hail or wind in a Class 1 area; however, it would be much more isolated and likely affect few homes.

Storm Classes Represent the Maximum Expected

It is important to note that the class shown on the PSAI weather map represents the maximum storm class to affect your specified geographic location. A storm class of 3, for example, means that the area may include all storm classes up to and including 3.

You can see how this works in the example below. The tag reads "Class 3 storm expected," and the swath includes classes 1, 2, and 3.

Breakdown of Storm Classes 1–5

Looking for a more precise definition of a particular storm class? Here is more information on each of the storm classes from low to high:

  • Class 1: The extreme weather characteristics are expected to be sporadic events in small isolated instances across the swath displayed in this region. Many small swaths are anticipated for the day of event forecast.
  • Class 2: Extreme weather events expected for this day should be less scattered and more widespread but still sporadic. On the day of this weather event, you can expect many different swaths for extreme hail and wind (instead of one large event covering the region in focus).
  • Class 3: Extreme weather events are expected to cover a large portion of the region displayed in this forecasted swath. On the day of the weather event, you will likely see larger and less scattered swaths for hail and wind.
  • Class 4: Extreme weather characteristics are expected (i.e. 58 MPH+ winds, 1"+ hail, and/or tornadic events) over much of the forecast swath.
  • Class 5: There are widespread extreme weather events expected to cover most of the region displayed in this forecast swath.