Isolated thunderstorms are individual storm cells that pop up in just a few spots, so most of the forecast area stays dry while a few places get a brief but intense storm. In forecasts, “isolated” usually means only a small chance that any one location will see a storm, often around 10–20% coverage.

Simple definition

  • An isolated thunderstorm is a single or small cluster of thunderstorms that is not part of a large, organized storm system.
  • They affect a small geographic area; nearby towns may have sunshine while one spot gets heavy rain and lightning.

How forecasters use “isolated”

  • When a forecast says “isolated thunderstorms,” it usually means storms will be “few and far between,” with low areal coverage (roughly 10–20% of the area may see a storm).
  • You can think of it as: most people in the region stay dry, but a lucky (or unlucky) few get a brief thunderstorm.

What they feel like

  • They can bring heavy rain, lightning, gusty winds, and sometimes small hail, but they are usually short‑lived (often under an hour).
  • They often appear suddenly on what otherwise looks like a mostly nice, warm, humid day, then fade away quickly.

Why and when they form

  • Isolated thunderstorms often form in warm, humid air with plenty of moisture and light winds that do not change much with height.
  • Solar heating during the afternoon is a key trigger, so they are most common in the late afternoon and early evening, especially in summer.

A quick mental picture

  • Imagine a clear sky with one big towering thundercloud off in the distance, “having the sky to itself” for many miles—that’s an isolated thunderstorm.
  • In contrast, if many such storms are scattered all over the region, coverage is higher and forecasters would usually say “scattered thunderstorms” instead of “isolated.”

TL;DR: “Isolated thunderstorms” means a low chance at your exact spot, but if one hits you, expect a short, sometimes intense burst of classic thunderstorm conditions.

Information gathered from public forums or data available on the internet and portrayed here.