Scattered vs Isolated Thunderstorms – What is the Difference?

Feb 03, 2013

As a weather junkie one of the questions I often get asked is what is the difference between Scattered and Isolated thunderstorms. Though not obvious, there actually is a difference.

First and foremost. Scattered vs isolated has NOTHING to do with the intensity or severity of the storms. Anytime thunderstorms are forecast for your area you should always pay more attention in case a severe threat exists.

Basically, scattered vs isolated comes down to the coverage of the storms over the forecast area. Scattered thunderstorms mean, at any one given time at least 30-50% of the area could be affected by thunderstorms. Typically these are the days where it will downpour for 5 minutes, then the sun comes out a few moments later, only to have it rain again 30 minutes later. The “off and on” type days that often feature multiple rounds of storms, sometimes lasting an entire day or more.

 

Here are some radar examples of what is expected when the forecast calls for scattered thunderstorms. As you can see the storms are scattered across the entire area, and more of the area is being affected at once.
If the forecast calls for isolated storms, then forecasters are expecting maybe only 1 round of storms, such as a squall line to move through and the remainder of the day to be storm free. There may be more than 1 storm complex in the area, but coverage is more limited to maybe 10 or 20% of the area.

 

Here are a couple radar examples of isolated storms. As you can see in the images below, one storm complex, no matter how big or small, evil or weak, dominates the area. Typically with these days you get one or 2 storms and then that is it. Also with isolated days, less area will experience storms, so while you may get dumped on at your house all your friends will complain they stayed inside all day because the forecast called for storms that didn’t form. Seems too simple for something weather related, so of course there are some exceptions such as a big squall line that may sweep through over an entire forecast area. Remember though, while the whole area gets effected by the squall line, it is not all at once, and typically the squall line will only be affecting a small portion of a larger area. Also there are times will the squall line moves through and then the storms are done for the day.

So while seemingly subtle, there is an actual difference between the two terms. It is not whatever term the guy on TV feels like using on any given day, but rather they are trying to give a suggestion as to how the storms may play out during the day. Now of course since we are dealing with the weather here, nothing is ever set in stone and the storms themselves don’t care if they are supposed to be isolated or scattered, they will do what they do.

Most importantly, if you are a storm lover and want to know which one offers a better chance for you to see storms, scattered storms will be your better chance.

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