I am a volunteer observer for the National Weather Service Cooperative Observer Program. My station is one of several thousand across the country kept by ordinary people: farmers, retired schoolteachers, a fellow who runs a water treatment plant, and me, a retired railroad signal maintainer. What we write down each morning becomes the official climate record for our towns. Nobody pays us. We do it because somebody has to, and because, if you keep at it long enough, the numbers begin to tell a story.

The shelter. The white wooden box on legs in the corner of the yard is an instrument shelter, the kind the Weather Service calls a "cotton region shelter." It has louvered sides so air moves through freely, a double roof to keep the sun off, and it stands so that the thermometers inside are about five feet above the ground. It is painted white to reflect sunlight, and the door faces north, so that when I open it in the morning the sun does not shine directly on the thermometers. It sits over grass, well away from the house, the driveway and the trees, because pavement radiates heat and trees trap it. The whole purpose of the shelter is to measure the temperature of the air, not the temperature of a box sitting in the sun. Put a thermometer on your porch in the sun and it will read 20 degrees too high; that is not weather, that is the porch.

The thermometers. Inside are two liquid-in-glass thermometers on a mount. The maximum thermometer is a mercury thermometer with a narrow constriction in the tube just above the bulb, like a medical fever thermometer. Mercury expands past the constriction as the air warms, but when it cools, the constriction keeps the column from falling back, so the thermometer holds the highest reading since I last reset it. I read it, then whirl it on its mount to force the mercury back down. The minimum thermometer is filled with alcohol and has a small dark glass index inside the column. As the alcohol contracts in cold, the surface of the liquid drags the index down; when it warms and expands, the alcohol flows past the index and leaves it behind. The far end of the index marks the lowest temperature. I read it, then tip the thermometer bulb-up so the index slides back to the surface. Each morning gives me the high and low of the previous 24 hours. Both thermometers are checked against a standard when the Weather Service representative visits, about once a year. (Some stations are being changed over to an electronic sensor with a readout in the house. I have asked to keep my glass ones as long as they last.)

The rain gauge. The standard gauge is a metal cylinder eight inches across, standing on a post in the open, with a funnel top that directs the rain into a narrow inner measuring tube. The tube has one-tenth the cross-section of the funnel, so one inch of rain fills ten inches of the tube. That lets me read the rainfall to the hundredth of an inch with a marked measuring stick, which I could not do with a plain bucket. If more than two inches fall, the tube overflows into the outer can and I measure the overflow separately by pouring it into the tube. Anything less than 0.01 inch is recorded as a trace, "T." In winter I take the funnel and tube out so snow falls into the big can; I melt it indoors and measure the water, and I measure the snow depth itself with a ruler on a white board I keep on the lawn for the purpose.

"Red sky at night, sailor's delight; red sky in morning, sailors take warning." — Mostly true, here. In the middle latitudes, weather moves from west to east. A red sunset means the setting sun in the west is shining through clear, dry, dusty air, so the weather coming toward you is fair. A red sunrise means the sun in the east is lighting up high clouds moving in from the west, or that the clear air has already passed you and moisture is behind. It fails when weather comes from an unusual direction, but I would put it at right two times out of three.

"A ring around the moon means rain soon." — True more often than not. The ring is a halo made by ice crystals in cirrostratus clouds, and cirrostratus is very often the leading edge of a warm front. In my ledger, a halo is followed by measurable rain within 36 hours a bit better than half the time. Not a promise, but better odds than a coin.

"Mackerel scales and mares' tails make tall ships carry low sails." — True, and the same idea. Cirrocumulus and cirrus spreading over the sky mean moisture and disturbance arriving high up, ahead of a front. Sailors were told to shorten sail because wind was likely within a day or two.

"When the dew is on the grass, rain will never come to pass." — Generally true. Heavy dew forms on clear, calm nights, and clear calm nights come with high pressure. High pressure usually means a fair day. No dew on a mild night means clouds or wind, which means a system is nearby.

"Rain before seven, fine by eleven." — Sometimes. A lot of rain comes in bands with a front, and a band that starts before dawn may well pass by mid-morning. But an all-day nimbostratus rain, like my September 11th, laughs at this one.

Counting cricket chirps to get the temperature. — True, and it surprised me. Count the chirps of a snowy tree cricket in 14 seconds and add 40, and you get the temperature in Fahrenheit, usually within a few degrees. Crickets are cold-blooded and chirp faster when warm. I have checked this against the shelter thermometer on summer evenings a dozen times. It works.

The woolly bear caterpillar's stripes forecast the winter. — No. I have looked, and the stripes vary from caterpillar to caterpillar in the same year. Nobody has ever shown they predict anything. Same for the thickness of corn husks, the height of hornets' nests, and what the groundhog does in February. Pleasant to talk about; do not plan your firewood by them.

Those forms, added up over a century, are the country's climate record. When you hear that a month was "the wettest August since 1951," it is a cooperative observer's ledger that says so. When the river forecasters need to know how much rain fell on the upper watershed last night, it is a farmer's gauge in a pasture that tells them. When an engineer designs a culvert, or a farmer picks a planting date, or a lawyer wants to know whether it was raining on a certain Tuesday in 1987, the answer comes from people like me.