Wind Gust vs Sustained Wind: What's the Difference?

A forecast says "winds 30 km/h, gusting to 60" while your own station shows 18 km/h. Neither number is wrong — they are measuring different things, in different ways, at different heights. This guide explains what sustained wind and wind gusts actually are, why forecasts always quote both, and why your home anemometer almost always reads lower than the official figure.

What is the difference between a wind gust and sustained wind?

Sustained wind is the average wind speed over a fixed period — two minutes for US National Weather Service observations, ten minutes under the WMO standard used in most of the world. A wind gust is a brief peak lasting only seconds, conventionally measured as a roughly 3-second average.

The gap between the two comes from turbulence. Friction with the ground, obstacles, and rising warm air break the airflow into eddies, so the wind arrives in surges rather than as a steady stream. Over open water the gap is small; over a town or a wooded valley, gusts commonly run far above the sustained speed. The National Weather Service publishes a short definition of wind gusts if you want the official phrasing — gusts are only reported when they exceed the sustained wind by a meaningful margin.

Why do forecasts give both a wind speed and a gust speed?

Because the two numbers answer different questions. The sustained wind describes general conditions — what cycling, sailing, or working outdoors will feel like for the next few hours. The gust figure describes the short, violent peaks, and it is the gusts that knock over garden furniture, snap branches, and drive rain into gaps.

A day of 30 km/h sustained wind with gusts to 45 is blustery but unremarkable. The same 30 km/h gusting to 70 is a different day entirely, even though the "wind speed" line on the forecast looks identical. When you are deciding whether to secure the trampoline, read the gust number, not the average.

Why does your home weather station read lower than the forecast?

Mostly mounting height. Official wind readings are taken at 10 m (33 ft) above open, unobstructed terrain. Wind speed drops off sharply close to the ground and around buildings and trees, so an anemometer on a garden pole or a rooftop bracket will usually read noticeably lower. That is expected behavior.

Friction slows the wind progressively as you get closer to the surface, and every fence, hedge, and neighboring roof carves out a sheltered wake. A station at 2–3 m in a suburban garden reading well below the airport figure is the normal case, not a broken sensor. The comparison you should care about is your station against itself over time, which stays consistent. If you want to narrow the gap, mounting position matters far more than sensor quality — the weather station siting guide covers where an anemometer should go and what ruins its data.

How do Davis stations measure gusts?

Davis stations transmit a fresh wind reading roughly every 2.5 seconds — fast enough to catch a gust that lasts only a few seconds. Stations that average wind over longer intervals of 10, 30, or 60 seconds smear those short peaks into the average, so their reported gusts run low.

The measurement itself comes from a cup anemometer paired with a wind vane: the cups spin at a rate proportional to wind speed, and the gust is simply the highest of those rapid samples in the reporting window. Sampling rate is one of the quiet specification differences between station tiers — two anemometers in the same garden can disagree on gusts purely because one looks more often. For more on what is actually inside the kit, see how weather station sensors work.

What wind speed causes damage?

As a rough guide, winds gusting above about 60 km/h (around 40 mph) start moving loose objects — garden furniture, bins, weak or dead branches. Gusts above about 90 km/h (around 55 mph) bring a real possibility of tree and structural damage. Exact thresholds vary with exposure, soil moisture, tree health, and building condition.

Treat these bands as prompts, not physics: a saturated lawn lets trees uproot at lower speeds, and a poorly fixed fence panel needs far less than a healthy roof. The practical habit is simple — when the forecast gust figure crosses the lower band, walk the garden and secure anything light. A wind gust email alert from your own station makes a good backstop for storms that arrive earlier or harder than forecast; setting up weather alerts on a home station walks through the options.

What do the Beaufort numbers mean?

The Beaufort scale translates wind speed into visible effects, from Beaufort 0 (calm, smoke rises vertically) to Beaufort 12 (hurricane force). It is defined on the sustained wind, not gusts — a Beaufort 5 afternoon over rough terrain can still produce gale-force gusts.

The scale is a useful sanity check for your own readings: if the trees outside are behaving like Beaufort 7 while your anemometer claims Beaufort 3, the sensor is probably badly sheltered.

How do gusts show up on your own charts?

Plotted together, average wind and gusts form two lines, and the vertical gap between them is your site's gustiness. A wide gap on a moderate day means turbulent, obstructed airflow; a narrow gap means clean exposure. Watching that gap over months tells you more about your site than any single reading.

Direction deserves the same treatment. On a Pro Weather site the wind rose is built from the raw per-tick samples rather than pre-averaged values, so the direction of brief gusts is not averaged away — a front's sudden westerly burst still shows in the pattern. If you have never used the chart, here is how to read a wind rose.

Common questions

What counts as a wind gust?

A gust is a sudden, brief rise in wind speed lasting a few seconds, conventionally measured as a roughly 3-second average. Weather services report a gust only when the peak exceeds the sustained wind by a meaningful margin — a steady breeze with tiny fluctuations does not get a gust figure at all.

How is sustained wind calculated?

Sustained wind is the mean wind speed over a fixed averaging period at the standard 10 m measuring height. US practice averages over 2 minutes; the WMO standard used in most other countries averages over 10 minutes. The same storm can therefore carry slightly different "sustained" numbers depending on which convention the reporting agency uses.

Why does my anemometer read lower than the forecast app?

Height and shelter. Forecast and airport winds refer to 10 m above open terrain, while most home anemometers sit at 2–6 m among buildings, fences, and trees that rob the wind of speed. Your gusts may also read low if your station samples wind infrequently. Compare trends, not absolute values, and improve mounting before blaming the sensor.

What wind speed is dangerous?

There is no single threshold, but risk climbs quickly once gusts pass roughly 60 km/h (40 mph), when loose objects and weak branches start to go. Beyond roughly 90 km/h (55 mph), trees can come down and buildings can suffer damage, especially with saturated ground or poor exposure. Local factors move these numbers substantially in both directions.