How Do Weather Stations Measure Rainfall?

Rainfall seems like a simple measurement, but getting it right requires careful mechanical design. The rain gauge on your weather station is a precision instrument that counts every drop, and understanding how it works helps you interpret the data correctly.

The tipping bucket mechanism

The most common rain gauge design in personal weather stations, including all Davis models, is the tipping bucket. It works like a tiny mechanical seesaw:

1. Rain falls into a funnel at the top of the gauge
2. The funnel channels water into one of two small buckets balanced on a pivot
3. When the bucket fills to a calibrated amount of rainfall, its weight tips it down. Davis sells two versions: a metric collector that tips every 0.2 mm and a US collector that tips every 0.01 inch (0.254 mm)
4. The tip empties that bucket and positions the other bucket under the funnel
5. Each tip generates a magnetic pulse that the station counts
6. The station multiplies the number of tips by that calibrated amount to calculate total rainfall

The process repeats for as long as it rains. The station tracks the total count and the rate (how many tips per minute, which gives you the rain rate).

What the station reports

From the tipping bucket mechanism, your weather station calculates three values:

• Rainfall today. The cumulative total since midnight.
• Rain rate. How fast rain is falling right now, calculated from the interval between tips. A high rain rate means the bucket is tipping rapidly, which indicates intense precipitation.
• Rainfall this event. The total from the current rain event (some stations reset this after a dry period).

These values are what you see displayed on your website and in your weather charts.

Accuracy and common issues

Tipping bucket gauges are mechanically simple and reliable, but they have known limitations:

• Undercatch in heavy rain. During intense downpours, some water can be lost during the bucket tip itself (when neither bucket is under the funnel). This is a known limitation of the design. Davis gauges minimise this with a fast-tip mechanism, but some undercatch is inevitable in extreme rain rates.
• Blockages. Debris, leaves, or insects in the funnel can block the water flow. A blocked gauge stops reporting until it is cleaned.
• Evaporation. In hot weather, a tiny amount of water can evaporate from the bucket before it tips, though this is negligible for most measurements.
• Splash. Heavy raindrops can splash out of the funnel, especially in windy conditions. Mounting the gauge at the correct height helps.
• Leveling. The gauge must be perfectly level. If it tilts, the bucket fill volumes become uneven and the measurement drifts.

Maintenance tips

Keeping your rain gauge accurate requires minimal but regular care:

• Clean the funnel every few months, especially after leaf fall or pollen season. Remove any debris and rinse with clean water.
• Check for insects. Small insects can nest in the funnel or bucket mechanism. A gentle rinse usually clears them.
• Ensure it is level. Use a spirit level on the top of the gauge. Adjust the mounting if needed.
• Inspect after storms. Heavy rain or hail can knock the gauge out of alignment.

How your weather data site displays rainfall

Once your station measures the rainfall and uploads it to WeatherLink, your website can display it in several useful ways. Pro Weather shows:

• Current rain rate with an intensity indicator
• Today's total with a visual progress bar
• Historical charts showing daily, weekly, monthly, and yearly totals
• Records for the highest rain rate, wettest day, wettest month, and wettest year
• Email alerts when rain rate crosses a threshold you define

All of this is calculated from those tiny bucket tips happening inside your gauge.

If you have a Davis station and want to see your rainfall data on a live, modern website with full historical charts, Pro Weather connects in minutes and stores your data forever.