Reading a weather map: station plots
A forecaster’s map isn’t covered in suns and clouds. Each weather station is drawn as a tiny code, a circle with numbers and a stick. Learn to read it, and you can see a whole province’s weather at a glance.
In this lesson
- Where each number sits on a station plot, and what it means
- Cloud cover in eighths of the sky (“oktas”)
- Reading wind barbs: direction and speed
- Decoding the pressure shorthand and the pressure tendency
The station model
Every station on a surface map is drawn the same way. Picture a small circle with numbers around it:
- The circle is the station. How much of it is filled in shows the cloud cover.
- Top left: the temperature.
- Bottom left: the dew point, the temperature the air would have to cool to before it’s saturated.
- Middle left, between them: a symbol for the present weather, such as dots for rain, stars for snow, commas for drizzle, three lines for fog.
- Top right: the sea-level pressure, in a shorthand.
- Right: the pressure tendency, how much the pressure has risen or fallen in the last three hours.
- The stick is the wind.
Cloud cover in oktas
Observers split the sky into eighths, called oktas. The station circle is filled to match:
- 0 oktas: empty circle, clear sky.
- 1 to 2 oktas: a small wedge filled: a few clouds.
- 3 to 4 oktas: about half filled: scattered cloud.
- 5 to 7 oktas: mostly filled: broken cloud.
- 8 oktas: completely filled: overcast.
- An X in the circle means the sky can’t be seen, for example in thick fog or heavy snow.
Wind barbs
- The stick points toward the direction the wind is coming from. A stick pointing to the upper left (northwest) means a northwest wind.
- The “feathers” on the end give the speed, in knots: a short half-feather is 5, a full feather is 10, and a solid triangle (pennant) is 50. Add them up.
- One knot is about 1.85 km/h. A quick way: double the knots and take off a bit. 20 knots is about 37 km/h.
- A circle around the station with no stick means calm.
On a chinook map, look for long sticks with lots of feathers pointing west or southwest across southern Alberta. Behind an Arctic front, the sticks swing around to the north or northeast.
Pressure: the shorthand
To save space, the pressure is written as three digits, with the leading 9 or 10 and the decimal point dropped.
- If the number is below 500, put a 10 in front: “132” means 1013.2 hPa.
- If it’s 500 or more, put a 9 in front: “980” means 998.0 hPa.
The pressure tendency is written the same way, in tenths: “+12” means the pressure has risen 1.2 hPa in the last three hours, and a little line symbol beside it shows whether it rose steadily, rose then fell, and so on. A big fall often means a low or a front is approaching.
Try it yourself
Decode this station plot (as you’d find it on a map):
- Circle three-quarters filled; temperature -4; dew point -7; a star symbol between them; pressure 214; tendency -18; stick pointing northeast with one full feather and one half-feather.
Answer: about 6 oktas, broken cloud; -4°C (25°F) with a dew point of -7°C (19°F); light snow; pressure 1021.4 hPa, falling 1.8 hPa in three hours; northeast wind at 15 knots (about 28 km/h). Falling pressure and a northeast wind in southern Alberta can mean upslope snow on the way.
Now print the free Western Canada station map from Weather Graphics and decode five stations near Lethbridge.
🏫 For teachers and parents
- Time: 40 to 60 minutes.
- Materials: printed symbols chart and station map, one per pair.
- Activity: “station plot bingo”: call out weather (“northwest wind, 20 knots, overcast, light snow”) and students draw the plot. Then swap and decode each other’s.
- Math link: converting knots to km/h, and decoding the pressure shorthand.
- Quick check: students draw the plot for the weather outside the classroom window right now.
Key terms
- Station plot
- The coded picture of one station’s weather on a map.
- Okta
- One eighth of the sky, used to measure cloud cover.
- Wind barb
- The stick and feathers showing wind direction and speed.
- Dew point
- The temperature air must cool to before it becomes saturated.
- Pressure tendency
- The change in pressure over the last three hours.
Check your understanding
1. A station’s pressure is written as “067”. What is the pressure?
067 is below 500, so put a 10 in front and add the decimal: 1006.7 hPa.
2. A wind barb has two full feathers and one half-feather. How fast is the wind?
10 + 10 + 5 = 25 knots, about 46 km/h.
3. The station circle is completely filled in. What’s the sky like?
A filled circle is 8 oktas: overcast. An X means the sky can’t be seen.
4. The temperature and dew point are both -2. What might you expect?
When temperature and dew point are equal, the air is saturated.
Sources: Weather Graphics weather reference chart (station model, symbols); Environment and Climate Change Canada surface analysis products.
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).