How to read wind direction without turning the arrows around
Wind direction usually names where the air comes from. Check the arrow legend before deciding where it is going.
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01The fundamental distinction
In the MET Norway data model, wind_from_direction means the direction the wind comes from, not the direction toward which it travels. A north wind moves from north toward south. An east wind moves from east toward west. That distinction matters before interpreting any number, label or chart.
A chart can use an arrow to show the incoming bearing or the direction of travel. Those are opposite conventions. Do not decide which one a chart uses from the arrow shape alone. Read its legend and the definition of the underlying field. The incoming bearing tells you where the flow comes from; a travel arrow tells you where it goes.
02Compass bearings and cardinal points
Wind direction is measured in degrees on a 360-degree compass scale. The cardinal points are fixed: 0 degrees is north, 90 degrees is east, 180 degrees is south, and 270 degrees is west. These values are absolute and do not change based on local geography or the user's orientation. A wind from 0 degrees is a northerly wind. A wind from 90 degrees is an easterly wind. A wind from 180 degrees is a southerly wind. A wind from 270 degrees is a westerly wind.
To visualize this without rotating arrows, imagine standing at the centre of a compass rose. The number reported is the point on the rim where the wind begins. If the number is 90, the wind starts at the east point and flows toward the centre, then continues toward the west. If the number is 270, the wind starts at the west point and flows toward the centre, then continues toward the east. This mental model avoids the need to physically turn a diagram or arrow. The user simply identifies the starting point on the compass and traces the path inward.
03Conceptual diagramming
A conceptual diagram for wind direction consists of a circle representing the compass. Mark the four cardinal points: North at the top, East at the right, South at the bottom, and West at the left. Place a dot at the centre representing the observer or the location of interest. To represent a wind from the north, draw a line from the top of the circle to the centre. To represent a wind from the east, draw a line from the right of the circle to the centre. The line indicates the path of the air mass.
This diagrammatic approach allows for quick verification of wind direction without complex calculations. If a forecast states the wind is from 45 degrees, the line originates from the northeast quadrant, halfway between north and east. The flow is toward the southwest. If the forecast states the wind is from 225 degrees, the line originates from the southwest quadrant, and the flow is toward the northeast. By keeping the origin point fixed on the rim and the destination at the centre, the user maintains a consistent frame of reference.
04Data model definitions
The MET Norway location forecast data model provides specific definitions for wind variables. The variable wind_from_direction is defined as the direction the wind comes from, with 0 degrees corresponding to north, 90 to east, 180 to south, and 270 to west. This definition is embedded in the data structure and must be respected by any software or human interpreting the output. Ignoring this definition and assuming the value represents the destination direction will result in a 180-degree error in interpretation.
The same data model defines wind_speed as a ten-minute average at ten metres above ground, expressed in metres per second. That definition belongs to the wind_speed field. Do not extend its averaging period to direction or gusts unless their own definitions support it. A forecast field is a model prediction, not a measurement made at your location.
05Forecast context and limitations
The location forecast service provides predictions for any coordinate for the next nine days. It is a forecast service, not a real-time measurement at the requested site. This distinction is vital. A forecast predicts what the wind will be based on model physics and initial conditions. It does not report what the wind is doing at this exact moment. Users must not confuse a forecast value with an observation. The accuracy of the forecast depends on the model resolution and the complexity of the local terrain.
Global forecasts use the ECMWF high-resolution model, but the coarse resolution warrants care with wind speed in complex topography. In mountainous or urban areas, local effects can cause significant deviations from the model output. The direction reported by the model is a large-scale approximation. It may not reflect the actual direction of the wind at a specific street or valley. Users should treat the forecast direction as a general tendency rather than a precise local vector.
06Practical interpretation questions
Consider a practical question: If a forecast reports a wind from 180 degrees, which way is the wind blowing? The answer is toward the north. The wind originates from the south and moves northward. If a user mistakenly interprets the 180 degrees as the destination, they would conclude the wind is blowing south, which is incorrect. This error is common and can have serious consequences in aviation or sailing. Always ask: where is the wind coming from?
Another hypothetical example: If the wind is from 90 degrees, it is an easterly wind. It blows from the east to the west. If the wind is from 270 degrees, it is a westerly wind. It blows from the west to the east. These examples illustrate the inverse relationship between the reported bearing and the direction of travel. The reported bearing is the source; the travel direction is the opposite. This inverse relationship is the core principle of wind direction interpretation.
07Avoiding common errors
Turning your body does not change a compass bearing. If a chart rotates with a map, check the map orientation before comparing it with the surroundings. A useful practical check is to locate north, identify the reported source bearing, and then trace the opposite direction of travel. Keeping those steps separate avoids confusing screen orientation with wind direction.
Another error is to assume that the wind direction value is relative to the local terrain. For example, in a valley, the wind may flow along the valley axis. However, the reported value is still a compass bearing. It is not aligned with the valley. Users must convert the compass bearing to a local frame if they wish to understand the wind relative to the terrain. This conversion requires knowledge of the local orientation. Without this knowledge, the compass bearing is the only reliable reference.
08Summary of interpretation rules
To summarize, the wind direction value in meteorological data is the compass bearing of the origin of the wind. 0 degrees is north, 90 is east, 180 is south, and 270 is west. The wind flows from this bearing toward the centre of the compass and then toward the opposite bearing. Users should visualize the wind as a vector originating from the rim of the compass and pointing inward. This visualization avoids the need to rotate arrows or diagrams.
The data model defines these variables explicitly. Users should consult the documentation for the specific model they are using to confirm the definitions. The MET Norway model, for example, clearly states that wind_from_direction is the direction the wind comes from. Adhering to this definition ensures accurate interpretation. Deviating from it leads to errors. By internalizing the distinction between origin and destination, users can read wind data with confidence and precision.
Questions
What does 'wind_from_direction' mean in the MET Norway data model?
In the MET Norway data model, 'wind_from_direction' means the direction the wind comes from. For example, a north wind moves from north toward south, and an east wind moves from east toward west. This distinction is crucial for accurate interpretation of wind data.
How are compass bearings used to measure wind direction?
Wind direction is measured in degrees on a 360-degree compass scale, where 0 degrees is north, 90 degrees is east, 180 degrees is south, and 270 degrees is west. These values are absolute and indicate the point on the compass from which the wind originates.
If a forecast reports a wind from 180 degrees, which way is the wind blowing?
If a forecast reports a wind from 180 degrees, the wind is blowing toward the north. This is because 180 degrees indicates the wind originates from the south and moves in the opposite direction, northward.
How can one avoid common errors when interpreting wind direction?
To avoid common errors, always locate north, identify the reported source bearing, and then trace the opposite direction of travel. It is important not to confuse screen orientation with wind direction or assume the value is relative to local terrain.
What is the core principle for interpreting wind direction?
The core principle for interpreting wind direction is understanding the inverse relationship between the reported bearing and the direction of travel. The reported bearing indicates the wind's source, and the wind travels in the opposite direction.
SOURCES
Modelled forecasts are planning support, not on-site measurement. Thresholds are commonly cited figures, attributed to their source — never statutory limits.