You woke up, looked out the window, and saw the patio furniture floating. Or maybe you just heard that rhythmic drumming on the roof all night and wondered if your sump pump was about to give up the ghost. It’s the first thing everyone asks over coffee: how much rain did we get last night? It seems like a simple question. It isn't.
Weather is weirdly local. You might have a deluge that drowns your tomatoes while your cousin three miles away only gets a light misting that barely clears the dust off their windshield. This is why checking the weather app on your phone—the one that pulls data from an airport fifteen miles away—usually feels like a lie. If you really want to know what happened while you were sleeping, you have to look at the intersection of automated sensor networks, "bucket" reports from neighbors, and the high-tech wizardry of dual-pol radar.
Why your phone app is probably wrong about last night's rain
Most people look at a generic weather app and see a single number. "0.5 inches." They look outside at a literal pond in their driveway and know that’s wrong.
The National Weather Service (NWS) relies heavily on ASOS—Automated Surface Observing Systems. These are those cluster-looking instruments you see at major airports like O'Hare, LAX, or Hartsfield-Jackson. They are incredibly accurate for that specific patch of tarmac. But rain, especially during summer thunderstorms or localized "training" cells (where storms follow each other like train cars), is notoriously patchy.
In 2024, a series of storms hit the Northeast where some towns in Connecticut recorded six inches of rain in three hours, while towns just ten miles north saw less than an inch. If you lived in the northern town but checked the "regional" report, you’d be baffled.
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The best places to find actual rainfall totals
If you're hunting for the truth, skip the generic "Sun & Clouds" icon app. You need the raw data.
CoCoRaHS is the gold standard.
The Community Collaborative Rain, Hail, and Snow Network (CoCoRaHS) is a volunteer-driven project. It’s basically thousands of weather nerds across the country who have high-quality, manual rain gauges in their yards. They wake up at 7:00 AM, check the tube, and log it. Honestly, it’s the most accurate ground-truth data available. You can go to their map, zoom in on your specific neighborhood, and see exactly what your neighbors measured. It’s far more reliable than a satellite estimate because someone actually saw the water in a physical container.
The NWS "Observed Precipitation" Map
The National Weather Service provides an interactive map that combines radar estimates with ground sensors. It’s updated frequently. If you want to know how much rain did we get last night, this is where the professionals go. You can toggle between the last 24 hours or even the last 7 days.
Personal Weather Stations (PWS)
Apps like Weather Underground allow you to tap into "Personal Weather Stations." These are people who bought a Davis or Ambient Weather station and hooked it up to the internet.
Sometimes these are great. Sometimes they are terrible.
If a neighbor has their rain gauge mounted under a tree or right next to a tall fence, their data is garbage. You have to look at a cluster of five or six stations in your area. If four of them say 1.2 inches and one says 0.2 inches, you know which one is the outlier.
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Understanding the "Rain Shadow" and local microclimates
Geography plays a massive role in why your backyard feels like a swamp while the next town over is bone dry.
If you live near a mountain range or even a significant set of hills, you might be experiencing the orographic effect. Air hits the hill, rises, cools, and dumps all its moisture on the windward side. By the time it gets to the other side—the leeward side—it’s dry.
Urban Heat Islands (UHI) also change the game. Big cities like Chicago or Houston create their own little weather bubbles. The heat radiating off the asphalt can actually "split" a storm cell or, conversely, intensify a storm as it passes over the city, leading to flash flooding in the urban core while the suburbs just get a breeze.
Why does it matter if it was one inch or three?
It isn't just about small talk. It’s about infrastructure.
One inch of rain on a one-acre lot is about 27,154 gallons of water. That is a staggering amount of weight and volume. If you got three inches last night, your soil is likely at "field capacity." This means it literally cannot hold any more water. Anything else that falls will immediately become runoff, which leads to:
- Foundation stress: Saturated soil expands and puts massive pressure on basement walls.
- Nitrogen leaching: If you just fertilized your lawn and got two inches of rain, your money just washed into the local creek.
- Septic issues: For those on a septic system, heavy rain can flood the leach field, meaning your drains might start gurgling or backing up.
The role of Dual-Pol Radar in modern reporting
In the old days, radar just measured "reflectivity"—how much of the beam bounced back. Big drops meant big rain. Simple.
Now, we use Dual-Polarization radar. It sends out both horizontal and vertical pulses. This allows meteorologists to see the shape of the drops. If the drops are flat like pancakes, it’s heavy rain. If they are tumbling and jagged, it’s hail. This tech has made the "estimated" rainfall totals on NWS maps significantly more accurate in the last decade. But even with lasers and satellites, it’s still an estimate.
Nothing beats a plastic tube in the ground.
How to measure your own rainfall accurately
If you’re tired of guessing, buy a manual rain gauge. The digital ones are cool because they sync to your phone, but the "tipping bucket" mechanism in many consumer-grade digital stations often misses the true total during extremely heavy downpours because the water splashes out before the bucket can tip.
A classic, clear plastic 4-inch diameter gauge (like the ones CoCoRaHS uses) is virtually foolproof.
Place it in the open. A good rule of thumb is to put it twice as far away from an object as the object is tall. If you have a 20-foot tree, put the gauge 40 feet away.
Actionable steps for the morning after
Stop guessing. If you had a heavy night of weather, here is exactly what you should do to verify the data and protect your property:
- Check the CoCoRaHS Map: Go to their website and look for your specific zip code. This gives you the most honest "ground truth" from human observers nearby.
- Inspect your "Low Spots": Walk the perimeter of your house. If water is standing within three feet of your foundation four hours after the rain stopped, you have a grading problem that needs to be fixed before the next storm.
- Clear the storm drains: Often, the "how much rain" question is less important than "where is the water going?" If leaves are clogging the street grate, your street becomes a lake regardless of the official total.
- Check your sump pump: If the local reports say you got over two inches, your pump has been working overtime. Listen for the cycle. If it’s huming but not moving water, the check valve might be stuck.
- Document for Insurance: If you have garden or property damage, take photos immediately. Mention the specific rainfall totals you found from official NWS or CoCoRaHS sources in your claim; it adds professional weight to your report.
The next time the sky opens up and you're lying in bed wondering how much rain did we get last night, remember that the answer isn't on a pretty icon on your iPhone. It’s in the data networks, the radar shapes, and that little plastic tube in the backyard.