Observing the Weather Yourself
Learn how to site a home weather station properly, what each sensor tells you, how to decode an airport report, and how your own observations can help science.
In this lesson
- What a home weather station measures, and how each sensor works
- Where to put sensors so the readings are honest
- How to read a METAR, the coded report airports issue
- Using radar and satellite images like a forecaster
- Citizen science: CoCoRaHS, CWOP and your own weather diary
Why your own observations matter
Official weather stations are spread thinly across the prairie. Lethbridge’s airport is south of the city, and weather can be quite different only a few kilometres away. A thunderstorm can drop hail on one neighbourhood and leave the next one dry. On a calm winter night, the river valley bottom can be several degrees colder than the tablelands above.
That is where home observers come in. The West Lethbridge Weather station, for example, is a Davis Vantage Pro 2 that has been recording conditions on the west side since 2007, with its wind sensor mounted on a 10 m tower. Stations like it fill in the gaps between official sites, and over the years they build a valuable local climate record.
What each sensor measures
- Temperature: an electronic sensor reads the air temperature. It must be shaded, because a thermometer in the sun measures sunshine, not air.
- Humidity: a hygrometer measures relative humidity, and the station calculates the dew point from it (see Lesson 5).
- Wind speed: an anemometer, usually three spinning cups. The faster they spin, the stronger the wind.
- Wind direction: a vane that points into the wind, reporting the direction the wind is coming from.
- Rain: most home stations use a tipping-bucket gauge. Rain funnels into a tiny seesaw that tips each time it fills with a set small amount, and the station counts the tips.
- Pressure: a barometer, often inside the indoor console, measures station pressure; the station converts it to sea-level pressure so it can be compared with other places (Lesson 3).
- Extras: some stations add solar radiation, UV, soil temperature or lightning detection.
An unheated tipping bucket cannot measure snow properly: snow piles up in the funnel or blows right past it, and is counted late or not at all when it melts. For snow, measure depth with a ruler in a few undisturbed spots, and if you can, melt a sample from a manual gauge to get its water equivalent.
Siting: where you put it matters more than what you buy
An expensive station in a bad spot gives worse data than a basic one in a good spot. The goal is to measure the air the way official stations do, so your numbers can be compared fairly.
The siting rules
- Temperature and humidity: about 1.25 to 2 m above the ground, over grass or natural ground, inside a white, louvred radiation shield (a fan-aspirated shield is even better). Keep it away from walls, decks, pavement, dryer vents and air conditioners, and never on a roof.
- Wind: the standard height is 10 m, in the open. Buildings and trees slow and twist the wind, so the farther the sensor is from them, the better. A common guideline is a clear distance of about ten times an obstacle’s height.
- Rain: mount the gauge level, under open sky, well away from trees and roofs. A rule of thumb is to keep it at least two to four times an obstacle’s height away from that obstacle.
Our strong winds make good siting even more important. Rain blown sideways and snow swirling past the funnel mean gauges here tend to catch less than actually fell on windy days. And on calm winter nights, cold air drains into the coulees and river valley, so two well-sited stations only a few kilometres apart can legitimately read very differently.
Reading an airport report: the METAR
Airports issue coded weather reports called METARs, usually every hour. They look like gibberish at first, but they follow a strict pattern. Lethbridge’s airport code is CYQL; Calgary is CYYC and Medicine Hat is CYXH.
A few quirks to know. Aviation uses its own units: wind in knots (multiply by about 1.85 for km/h, so 37 knots is roughly 69 km/h and the 52-knot gust is about 96 km/h), visibility in statute miles, cloud heights in feet, and pressure as an “altimeter setting” in inches of mercury (29.61 is about 1003 hPa). Wind direction is where it is coming from, in degrees: 270 is due west. “M” means minus. Times are in UTC, so 1800Z is noon in Alberta (Alberta Time is UTC minus 6 all year). Canadian METARs often end with a remarks section (RMK) listing cloud types and the sea-level pressure in hectopascals.
Radar and satellite: seeing the big picture
Radar sends out pulses of microwave energy and listens for echoes bouncing off raindrops, hail and snowflakes. Stronger echoes mean heavier precipitation. Always play the animation, not just the still image, to see which way storms are moving. Remember that the radar beam climbs higher with distance, so it can overshoot light snow from low clouds far from the radar, and mountains can block it.
Satellite images come in three main flavours. Visible images are like a photograph and only work in daylight. Infrared images measure the temperature of cloud tops, so they work day and night; the coldest, brightest tops belong to the tallest storms. Water vapour images show moisture high in the atmosphere and reveal the swirls of the jet stream.
On a chinook day, look at a visible satellite image of southern Alberta. You can often see a sharp cloud edge running parallel to the Rockies, with clear skies between it and the mountains: the chinook arch, seen from above.
Join in: citizen science and your weather diary
CoCoRaHS (the Community Collaborative Rain, Hail and Snow Network) is a volunteer network that operates in Canada as well as the United States. Volunteers use a standard manual rain gauge, check it each morning and report rain, snow and hail online. The reports help researchers, forecasters, farmers and water managers, and hail reports are especially valuable in Alberta. All you need is a gauge, an open spot in your yard and a few minutes a day.
CWOP (the Citizen Weather Observer Program) lets owners of home weather stations share their readings automatically over the internet. The program is run in partnership with the U.S. National Oceanic and Atmospheric Administration but accepts stations from other countries, including Canada. Readings are quality-checked and made available to forecasters and researchers.
Keep a weather diary
You do not need any equipment to start. Each day, jot down the date, time, temperature, sky, wind and anything you notice: the first frost, the first snow, a chinook arch, the first crocus, a hailstorm. Add photos. Compare what happened with what was forecast. After a few years, your diary becomes a personal climate record of your own corner of southern Alberta, and you will start to see patterns no app can show you.
Try it yourself
Find today’s METAR for CYQL (NAV CANADA’s aviation weather website and many free apps show it) and decode it using the example above. Then compare its temperature, wind and pressure with the live West Lethbridge readings. Are the differences what you would expect, given that the two stations sit in different parts of the city?
West Lethbridge now (4:08 am): 0°C, wind calm, humidity 94%. Live station ›
Key terms
- Radiation shield
- A white, louvred housing that shades a temperature sensor from the sun while letting air flow through.
- Anemometer
- The instrument that measures wind speed, usually with spinning cups.
- Tipping-bucket gauge
- A rain gauge with a tiny seesaw that tips each time it collects a set amount of water, counting rainfall automatically.
- METAR
- A coded, usually hourly, weather report issued by airports.
- UTC (Z time)
- Coordinated Universal Time, the single world clock used in weather and aviation.
- Infrared satellite image
- A picture of cloud-top temperatures that works day and night; colder tops mean taller clouds.
- CoCoRaHS
- A volunteer network that measures and reports daily rain, hail and snow, active in Canada and the U.S.
- CWOP
- The Citizen Weather Observer Program, which collects data from home weather stations.
Check your understanding
1. At what height should a home station’s temperature sensor be mounted?
The standard height for temperature is about 1.25 to 2 m over grass, so readings match official stations. Ten metres is the standard for wind.
2. Why should you not mount a temperature sensor against the south wall of your house?
Sun-warmed walls radiate heat, and houses leak heat, both of which push readings above the true air temperature.
3. In the METAR wind group “26037G52KT”, what does “G52” mean?
The group reads: from 260 degrees, at 37 knots, gusting (G) to 52 knots (KT).
4. Which satellite image works at night and shows how cold, and therefore how tall, cloud tops are?
Infrared images measure the temperature of cloud tops, so they work day and night; the coldest tops belong to the tallest clouds.
5. What do CoCoRaHS volunteers do?
CoCoRaHS volunteers use a standard manual gauge and report precipitation every morning, filling gaps between official stations.
Weather School is for learning and enjoyment. It is not official guidance and may contain errors. For watches and warnings, always use Environment Canada (WeatherCAN app or weather.gc.ca).