Isolated vs. scattered vs. widespread thunderstorms: What’s the difference?

The meaning of the words isolated, scattered and widespread is a common source of confusion in weather forecasting.  Let’s clear the air.

At the Capital Weather Gang, when we forecast isolated showers or storms, we mean there is a 25 percent or less chance of getting wet at any given location. If isolated storms are in the forecast, it’s smart to keep an eye to the sky and on radar, but chances are you’ll stay dry.

Here’s what radar might look like for an isolated shower and storm scenario:

(Radar Scope)
(Radar Scope)

When we forecast widely scattered showers and storms, that conveys a 30-40 percent chance of rain.  It’s more likely than not storms will avoid you in this scenario, but you’re by no means in the clear.  An example radar:

(Radar Scope)
(Radar Scope)

A forecast for scattered showers and storms suggests rain chances in the range of 40-60 percent.  Whether you get rained on or not is essentially a crap shoot.  Here’s what scattered showers look like:

(RadarScope)
(RadarScope)

When we forecast widespread showers and storms, chances are very good – greater than 60 percent – most of the area will be affected.  This is not a good day for an outdoor party or, you better have a backup plan indoors.  Here’s a case of widespread activity:

(Radar Scope)
(Radar Scope)

It’s important to note these terms only convey information about storm coverage, not their intensity or the hazards associated with them.  Also, it doesn’t tell you anything about their timing.   A complete forecast must include all information about intensity, associated hazards, timing AND coverage ; but hopefully the above guide provides some clarity on what we mean by the words we use to describe coverage.

Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.
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