How to read a meteogram: speed, gust and direction on one chart

The primary feature of a meteogram is often a line graph representing the forecast wind speed. This line typically shows the average wind speed at a standard height, commonly 10 metres above ground level, averaged over a 10-minute period. The vertical axis indicates wind speed, often in metres per second (m/s) or knots, while the horizontal axis represents time, usually in hourly or three-hourly increments over several days.

For example, if the line shows 8 m/s at 14:00 on Tuesday, this indicates an average wind speed of 8 metres per second at that time. This is the sustained wind, not the peak gust. Your operational limits, such as a commonly cited 10 m/s for some elevated work, should be compared against this sustained speed. Remember, your own document governs the limits for your specific work.

Overlaying the average wind speed line, a shaded area or a separate line often represents the forecast wind gusts. Gusts are short, abrupt increases in wind speed, typically lasting a few seconds. The gust band illustrates the expected range of these peak speeds. For instance, if the average wind speed is 8 m/s and the gust band extends to 14 m/s, it means that while the wind will generally be 8 m/s, momentary bursts up to 14 m/s are anticipated.

Understanding the gust factor - the ratio of gust speed to average speed - is vital. A higher gust factor indicates more turbulent conditions. The Wind Agent's exceedance fan uses ensemble member fractions to show the likelihood that the wind, including gusts, will exceed your specific limits, helping you assess risk against your own operational thresholds. For more on this, see our article on Gusts and turbulence.

Wind direction is typically indicated by arrows or 'wind barbs' placed along the timeline. These symbols point in the direction the wind is coming from, following meteorological convention (e.g., an arrow pointing from west to east indicates a westerly wind). The orientation of these arrows reveals shifts in wind direction over time. A clockwise shift in direction is known as 'veering', while an anti-clockwise shift is 'backing'.

For example, if arrows change from pointing from the south-west to pointing from the north-west, this represents a veer. Significant shifts in direction can indicate the passage of weather fronts or changes in synoptic patterns. The Agreement Spine on The Wind Agent instrument provides a measure of consistency across different forecast models, which can be particularly useful when anticipating complex directional changes. For a deeper dive into directional changes, consider Veer and back: wind direction change.

Meteograms can effectively highlight the passage of weather fronts. A typical frontal passage might appear as:

• A sudden increase in wind speed: The average wind speed line and gust band may show an abrupt upward spike.
• A distinct shift in wind direction: The wind arrows will show a clear veer or back over a short timeframe.
• Changes in other parameters: While not strictly wind-related, a front often brings changes in temperature, precipitation, and pressure, which might also be visible on a more comprehensive meteogram.

For instance, a cold front often brings a sharp veer in wind direction (e.g., from south-westerly to north-westerly) and a sudden increase in wind speed, followed by a drop in temperature. Recognising these patterns helps in anticipating operational challenges.

Most meteograms represent wind at a standard height, typically 10 metres. However, wind speed changes with height due to surface friction, a phenomenon known as wind shear. The Wind Agent's Shear Glass provides height-matched wind speeds at 10, 80, 120, and 180 metres. This is crucial for operations at elevated heights, where wind speeds can be significantly higher than at 10 metres.

For example, if the 10-metre wind is 5 m/s, the wind at 120 metres could be 8 m/s or more, depending on atmospheric stability and surface roughness. Comparing your operational height to the standard 10-metre forecast is essential. Your own document governs height-specific limits. The Shear Glass uses established models like the log or power law to estimate these height-adjusted speeds. For more information on how location affects wind readings, see Siting and exposure: why location changes the reading.

A single meteogram typically shows a deterministic forecast - one possible future. However, weather forecasting inherently involves uncertainty. The Wind Agent provides ensemble exceedance odds, which are member fractions from multiple forecast model runs. These show the chance that the wind will exceed your specified limit, not as a calibrated probability, but as a proportion of ensemble members predicting exceedance.

If 30 out of 50 ensemble members predict wind speeds above your 12 m/s limit, the exceedance odds are 60%. This offers a more nuanced view of risk than a single forecast line. For example, if the deterministic forecast shows 9 m/s but the ensemble exceedance odds for 12 m/s are 70%, it suggests a significant chance that the wind will be stronger than the single forecast indicates, prompting a more cautious approach. This is an important distinction when considering the reliability of any Reading a meteogram.

Forecasts presented in meteograms are derived from numerical weather models. These models operate on grids, and their resolution (the spacing between grid points) affects the detail and accuracy of the forecast, especially in complex terrain. A global forecast, even from high-resolution models like ECMWF, will not capture local topographical effects as precisely as a very high-resolution regional model.

It is important to remember that these are model predictions, not actual site measurements. The Wind Agent's grounded agent feature helps bridge this gap by providing real-time local measurements to complement the forecast. For further reading on how models work, see Resolution and grids.

Beyond the meteogram, The Wind Agent instrument offers additional features to support your decisions. Evidence records capture historical wind data, allowing for post-event analysis and compliance documentation. The fleet board provides an overview of conditions across multiple locations, which is invaluable for managing distributed operations. These features, combined with the detailed meteogram, empower you to make informed decisions based on comprehensive wind intelligence, always measured against your own defined limits and procedures.