What does the big number mean?
The big number is the modelled mean wind speed at your working height for the hour you have selected. This guide explains the unit line, the direction text, the 10 m gust, how height and fidelity change it, and what a dash means.
ON THIS PAGE
01What the number is
The hero readout opens with the words "Primary wind at" and your working height. Beneath is the large number, followed by your display unit and the height again, for example "mph at 80 m". It is the mean wind speed from the primary forecast model, read at the height shown in the Height stepper, for the hour selected on the time strip. It is not a gust, not a forecast for ground level and not an observation. Change the height and the number changes; change the hour and it changes again.
02The direction line
Under the number is a line such as "FROM 270° · BLOWS ENE". The first part is the meteorological bearing the wind comes from, in degrees true, written with three digits. The second part is the compass point the wind is heading toward, the opposite direction. A wind from 270 degrees is a westerly, and it blows toward the east. If the direction is unknown, dashes stand in for the bearing and the compass point.
03The gust and the odds
A row beneath shows "GUST 10 m" and a value. This gust is always the 10 m gust from the model, whatever your working height. Models define gust only at 10 m, so there is no gust at 80 m to show; the label says 10 m so you do not mistake it. On the right of the row is the odds figure: "P(>limit) · set your limit" when no limit is set, or "P(>" and your limit with a percentage, and EXCEED when it is 40% or more. A dash in its place means odds could not be computed.
04Height, and how it is worked out
The model provides wind at 10, 80, 120 and 180 m. If your height is one of those the value is read directly. Between them it is interpolated on a log-height scale. Below 10 m or above 180 m it is extrapolated using a neutral log law, and the instrument labels it. These labels are in the wind-profile glass, in the inspector on desktop: "Native model level", "Interpolated between native levels (log-height)", "EXTRAPOLATED · outside 10 to 180 m, log law" or "UNKNOWN · no usable level". Small notes about the method can also appear under the hero.
05The hour
The number follows the time strip. At first it shows the current hour. Drag the strip, or use the arrow keys, and the hero, the lamp and the odds all move to the selected hour. The title at the left of the time bar shows the hour and "SITE TIME", so you can confirm which hour you are reading. Times are in the site timezone, not your own.
06Why it differs from a weather app
Most apps show wind at 10 m, and often gust. The hero shows mean speed at your height, which is usually higher than 10 m wind because wind increases with height, with the exact ratio depending on conditions and terrain. A crane jib at 80 m and a person on the ground at the same pin should not see the same number. Different models and different averaging also move figures by a few miles per hour.
07A dash and UNKNOWN
If the instrument cannot compute a value, the number is replaced by a dash and a note reading "UNKNOWN" with the reason, such as no usable level. That is not zero wind. A missing value is never shown as calm, because showing a figure the data does not support could mislead. The lamp also turns to UNKNOWN or NO LIMIT in these cases. Try another hour, another height, or reload.
08Common misreadings
The common mistakes are: reading the number as ground level, reading the 10 m gust as a gust at height, forgetting that the hour has been scrubbed, and treating a calm-looking number as a decision. The number is data. Compare it with the limit you typed, look at the odds and the fan, and apply your own document. The decision stays with the person responsible on site.
Questions
Why does the number change when I change the height?
Because wind speed generally rises with height above the ground, and the instrument reads the model levels at 10, 80, 120 and 180 m and works out your height from them. Values inside 10 to 180 m are native or interpolated, and outside that range they are extrapolated and labelled as such.
Is the gust at my working height?
No. The gust shown is always the 10 m gust, labelled "GUST 10 m". Forecast models define gust at 10 m only. If your limit is a gust at height in your documents, treat the 10 m gust as a reference only, and see the limit and rule guides for how gust rules work at other heights.
Can it tell me whether it is fine to lift, spray or fly?
No. It reports modelled wind and the odds of reaching the limit you typed in. The limit comes from your own document, such as a manufacturer's manual, a method statement or a permit. The decision stays with the person responsible on site.
Why does it show a dash instead of zero?
A missing value is not calm. If a model level is absent or the data failed to load, the number becomes a dash with an UNKNOWN note, and the odds are not computed. A zero would suggest there is no wind when the truth is that there is no data.
Which model does the number come from?
It comes from the primary forecast, the best-match blend that the weather service provides, with ICON, GFS and ECMWF IFS used for the agreement check. The source and the fetch time are written at the bottom of the inspector, in the provenance note, which also says it is a modelled forecast and not an observation.