Week 07 · Precipitation

Wednesday

Station Lab: The jar rain gauge

// Rain, snow, sleet, freezing rain and hail

⏱ about 20 min

Wednesday: Station Lab: The Jar Rain Gauge

Rocket sets three jars on the lab table: a wide bowl, a skinny vase and a straight-sided jar.

"After the next rain, we measure," he says. "Whichever jar has the most water wins."

Raven frowns at the bowl. "What do you notice about the shapes?"

"The bowl is wide at the top and narrow at the bottom," Rocket says. "So the water would look deeper than it really is."

Nova glides along the row of jars. "A good gauge gives the same depth the ground received," she says. "Which shape does that?"

Rocket slides the straight-sided jar to the center. "Same width top to bottom. This one is Station Rooftop's official gauge."

Your mission

You will build a rain gauge from a straight-sided jar. Then you will test it with a known amount of water before any rain falls.

Weather observers read rain to the hundredth of an inch. Your gauge will be rougher, but it will be honest.

A clear, straight-sided jar or cup (the same width at the top and bottom)
A ruler marked in inches or millimeters
A measuring cup and some tap water
Waterproof tape or a marker that writes on glass or plastic
A small tray of pebbles or a bucket to keep the jar from tipping
Your weather log

Safety first

If a bottle needs cutting, a grown-up does it. Taped edges keep fingers safe.
The gauge sits on the ground, a railing or a windowsill, never on a roof or up a ladder.
Never go outside during a thunderstorm or high wind to check it. Read the gauge after the weather has passed.
The water in the gauge is for measuring, not drinking. Pour it out when you are done.

Check the jar: measure its width at the top and at the bottom. The two numbers should match.
Stand the ruler inside the jar, or tape it to the outside with the zero mark level with the inside bottom.
Pour exactly one cup of water into the jar and read the depth. Write it down.
Pour in a second cup and read again. The depth should have doubled.
Empty the jar. Set it in an open spot away from walls, trees and roof edges, weighted so it cannot tip.
After the next rain ends, read the depth to the nearest small mark and write it in your log with the date.
Empty the jar after every reading so each day starts at zero.

Test	Water added	Depth you read
1	One cup
2	Two cups
Rain day 1	Unknown
Rain day 2	Unknown

PREDICT BEFORE YOU POUR

Read the question.
Tap your answer.

You pour a second cup into a straight-sided jar. What happens to the depth?

The same rain falls into a wide bowl and a straight jar. Which reading matches the depth on the ground?

How the professionals do it

The National Weather Service standard rain gauge has a funnel eight inches across that leads into a narrow measuring tube.

One inch of rain fills the tube to a depth of ten inches, so tiny amounts are easy to read.

Observers read a measuring stick to the hundredth of an inch, for example 1.34 inch.

More than 8,700 volunteers take daily readings of temperature, snowfall and 24-hour precipitation for the Weather Service.

A good rain gauge has the same ____ at the top and the bottom.

In the standard gauge, one inch of rain fills the tube to how many inches? Type a number.

Record your two test depths. Did the second reading double the first? If not, what about your jar could explain it?After the next rain, record the depth and the time you read it. Also note what the sky looked like when the rain ended.

Draw your finished gauge with labels: the jar, the ruler, the zero mark and the open spot where it sits.

Great lab work. Tomorrow you read real drop size data and compare your gauge with an official report.

Grown-up checked my answers

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