How Can Rainfall Vary So Much Just a Few Miles Apart?

Have you ever had a heavy downpour at your house, only to talk to someone a few miles away who barely got any rain?

It can seem strange, especially when both places were supposedly under the same rainstorm. But rainfall can vary considerably over surprisingly short distances. This is especially common with summer showers and thunderstorms.

Rain Doesn't Fall Evenly

It's tempting to picture a rainstorm as one large cloud spreading rain evenly over everything below it. That's often not what happens.

Showers and thunderstorms can contain areas of very heavy rain right next to areas receiving much lighter rain. If the heaviest part of a storm passes directly over your house, you may get a soaking. A neighborhood only a few miles away may catch the edge of the same storm and receive very little.

Sometimes the difference can be even more dramatic: one place gets a downpour while another nearby stays completely dry.

Thunderstorms Can Be Very Localized

Summer thunderstorms are particularly good at producing these differences because individual storm cells can be relatively small and can change quickly.

A storm may strengthen as it approaches one area, produce heavy rain for a short time, and then weaken as it moves away. New cells can also develop while others disappear.

The path matters, too. A narrow band of heavy rain doesn't have to shift very far for one neighborhood to receive much more water than another.

This is why watching a dark cloud nearby doesn't necessarily mean you're going to get the rain—and why you can sometimes hear thunder while standing under blue sky.

Wind Can Make the Pattern Even More Complicated

Rain doesn't necessarily fall straight down from the spot where it formed. Wind can carry falling raindrops sideways as they travel toward the ground, particularly during thunderstorms.

Storms themselves are also moving, sometimes quickly. The combination of a moving storm, changing rainfall intensity and wind can create a patchwork of rainfall totals across a relatively small area.

Two Nearby Rain Gauges Can Both Be Right

This is one reason two properly placed rain gauges a few miles apart can record very different totals.

If one gauge records 1.2 inches and another records 0.6 inch, that doesn't automatically mean one of them is wrong. They may simply have experienced different parts of the storm.

The same thing helps explain why the amount in your rain gauge may not match the rainfall total reported by a nearby weather station or your weather app. That number may accurately represent rainfall at another location without accurately representing what fell at your house.

Rainfall Can Even Vary Around Your Yard

You don't always have to travel a few miles to get a different rainfall reading. Two rain gauges in the same yard can sometimes collect slightly different amounts, especially during a windy or fast-moving storm.

Some of that difference can come from the rain itself. Wind can push falling rain at an angle, and brief, intense bursts of rain don't necessarily pass evenly over every part of a property. But placement matters too. Trees, buildings, fences and other nearby objects can block or redirect wind and rain, causing one gauge to catch more or less water than another.

That's why two gauges don't have to show exactly the same amount to both be working properly. Small differences are normal. Larger differences are a good reason to check whether one gauge is too close to a tree, roof, wall or other obstruction.

Fun Fact: Weather radar is extremely useful for seeing where rain is falling, but the rainfall amounts it shows are estimates. A small, intense downpour can produce much more rain at one location than the radar estimate suggests. A properly placed rain gauge measures what actually reached the ground at that particular spot.

What About Microclimates and Rain Shadows?

Rainfall can also vary from place to place for longer-term reasons.

Local differences in elevation, vegetation, bodies of water, buildings and other features can create microclimates. On a larger scale, certain structures and mountains can create a rain shadow, with much wetter conditions on one side of a mountain range and much drier conditions on the other.

Those are persistent geographic influences. The big differences you see after a single summer thunderstorm can be much simpler: the heaviest rain just didn't fall in the same place.

That's one of the most interesting things about measuring rainfall locally. A regional forecast can tell you that rain is coming, but what actually falls at your house can be a very local event.