4 Rain Sizes in Las Vegas and What Each Does to a House

A normal year at the Las Vegas airport brings 4.18 inches of rain, and a normal November brings 0.30 inch.¹ So when the National Weather Service forecast from Wednesday, November 11 put a 50 percent chance of rain on Friday night, November 13, with a second system behind it on Monday, the fair question is how big.² Most Las Vegas rain is too small to flood a house, but it’s big enough to leak into one, and a flash flood depends on how fast the rain falls, not on the day’s total. We sorted 20 years of airport rain days by size so you can match the forecast to what it does to a home.

What the Forecast Called for on November 13 to 17

The forecast office in Las Vegas described two systems. The first one brings a chance of showers late Friday into Saturday. The second arrives Monday into Tuesday with a wider chance of rain.²

The numbers were small. The forecast grid for central Las Vegas showed about 0.06 inch from Friday night into Saturday morning, and about 0.15 inch from Monday afternoon into Tuesday morning.² The forecasters wrote that they were growing more confident in at least some light rain at desert elevations.²

No flood watch was in effect for the valley when that forecast came out. Forecasts move, so look at the current one before you plan around it.²

November can still surprise you. Last year the airport took 0.65 inch on November 15 and 0.55 inch on November 18, each one well over the normal for the whole month.¹

And the wettest day of 2026 so far was only a month ago. On Sunday, October 11 the airport gauge caught 1.08 inches, which tied the wettest October day in the airport record we pulled back to 1937.¹

The 4 Rain Sizes at the Las Vegas Airport

We counted every day with measurable rain at the airport from 2006 through 2025, using the National Weather Service daily record.¹ There were 455 of them, about 23 a year. Days with only a trace were left out.

Under a Tenth of an Inch

This is the common one. It covers 269 of the 455 days, or about 6 in 10.¹ Friday night’s forecast amount sits in this group.

It wets the roof, the walls and the street. It doesn’t pond. What it does is test every gap that has opened up since the last rain, like a cracked roof tile, a dried out window seal or a lifted piece of flashing.

A Tenth to a Quarter Inch

This size showed up on 97 days, about 5 a year.¹ Monday’s forecast amount sits here.

Now there’s enough water to run. Gutters and roof drains carry a steady stream, and low spots on a patio or along a block wall start to hold water. A slow drip at a ceiling stain becomes a wet ring.

A Quarter to a Half Inch

This size showed up on 59 days, about 3 a year.¹

Yards and driveways shed water toward the street, and anything graded toward the house shows it. Water finds the bottom of the garage door and the track of a sliding door.

Half an Inch or More

This is the rare one. It came on 30 days in 20 years, about 3 every 2 years, and only 5 of those days reached a full inch.¹ October 11 of this year made it 6.

These are the days when streets run curb to curb and washes fill. Whether your street floods depends on what comes next, which is how fast it fell and where.

A Flash Flood Is About Speed, Not the Day’s Total

The National Weather Service defines a flash flood as a flood caused by heavy rain in a short period, generally less than 6 hours.³ The clock matters more than the gauge.

A half inch spread over a gray winter day soaks in and drains off. The same half inch in 20 minutes over one part of town becomes a river in the street. The airport total can’t tell you which one you got, and it can’t tell you what fell on your side of town.

The ground makes it worse. Desert Research Institute scientists point out that as concrete and pavement replace porous desert soil, flood risk in the valley rises.⁶

The valley is built for this. The Clark County Regional Flood Control District says its system now includes 113 detention basins and more than 722 miles of channels and underground storm drains, and that about 75 percent of the planned system is finished.⁵

That system protects neighborhoods, not individual roofs. And the last quarter of it isn’t built yet.

Winter counts too. The district names July through September as the months for sudden downpours.⁴ But the Desert Research Institute study found that floods here now happen more often in winter than they used to, and that daily rain amounts have gone up in winter since 1950.⁶

On the road, the district’s numbers are blunt. Six inches of water is enough to make you lose control of a vehicle, and one foot can float most cars.⁴

What a Tenth of an Inch Does on a 2,000 Square Foot Roof

Small rain is still a lot of water once a roof collects it. The US Geological Survey figures that one inch of rain on a 40 by 70 foot roof is 1,743 gallons.⁷

Scale that to a 2,000 square foot roof and you get our math below. It’s an example, not a measurement of your house.

• 0.06 inch, Friday night’s forecast amount, is about 75 gallons.
• 0.15 inch, Monday’s forecast amount, is about 190 gallons.
• 0.50 inch is about 620 gallons.
• 1.08 inches, the October 11 total, is about 1,340 gallons.

Even the smallest forecast puts about 75 gallons on that roof, and all of it leaves by the same few paths. If one of those paths is blocked or cracked, the water goes into the house instead.

So after a light rain, walk the house once with a flashlight.

• Ceilings under roof valleys, vents and skylights. A new stain or a damp ring is the sign, and our guide on how a small ceiling stain grows covers what to do next.
• Window sills and the carpet under them. Our door and window leak guide shows the clues.
• The track and the floor at each sliding door.
• The inside edge of the garage door and the base of the garage walls.
• The attic, if you can get a safe look, for dark or damp wood.

Speed matters once you find something wet. The EPA says to dry water damaged areas and items within 24 to 48 hours to prevent mold growth.⁸

When Rain Turns Into a Flood Claim

Rain through the roof and floodwater through the door are not the same thing to an insurer. FEMA’s FloodSmart site says most homeowners insurance does not cover flood damage.⁹

It describes a flood as an excess of water on land that is normally dry, affecting two or more acres or two or more properties.⁹ Street water that rises into the garage fits that. A drip from the ceiling is a different question, so ask your agent how your own policy treats each one.

You can’t buy your way out the week of a storm. A new flood policy usually takes effect 30 days after you buy it, with a few exceptions such as a policy bought with a new mortgage.¹⁰

And living outside a mapped flood zone doesn’t clear you. The flood control district says 20 to 25 percent of National Flood Insurance Program claims come from outside the high risk areas.¹¹

If water does come in, photos first, then cleanup. Our insurance claims page walks through the paperwork, and the flood damage restoration page and storm damage page show how the drying runs.

We’d rather you spend ten minutes with a flashlight after a light rain than find the stain in January. Size the rain first, then check the spots that size reaches.

Things to Settle

Studies and Pages

Pick RemediationX as a Preferred Source on Google