// Weather in the tower

Met display

The tower met display: wind, QNH and QFE, temperature, cloud base and RVR, how the numbers are averaged, and what Prestwick’s METAR shows right now.

What it is

CAP 670 requires a met display showing at least wind, pressure and temperature (ATC01.7), surface wind indicators showing speed and direction (ATC01.9) and an outside air temperature display (ATC01.12).
A cloud base recorder (ceilometer) is mandatory at licensed aerodromes with precision-approach runways; its display goes in the tower as an aid to the observer, with 100 ft resolution (CAP 746).

How controllers use it

Wind sensors are sampled at least 4 times a second, giving a 3-second gust and 2- and 10-minute averages (CAP 746).
Take-off and landing reports use degrees magnetic, a 2-minute average, and gust/lull over 10 minutes. METAR wind is a 10-minute mean in degrees true (CAP 493). “Instant” wind means a value that is not the 2-minute average.
QNH and QFE are rounded down. METAR does not include QFE.

UK rules and practice

METARs are issued every 30 minutes and sent to NATS via the AFS (CAP 746). AUTO METAR needs CAA permission.

At Prestwick

Associated met office: Met Office Exeter. Anemometers sit next to both ILS glidepath aerials.
The AIP warns that low-level mechanical turbulence can make the reported wind lower than pilots experience.
The panel on this page shows the latest EGPK METAR from the site’s weather feed, so its wind is the METAR 10-minute mean in degrees true, not the 2-minute magnetic wind a controller would read out.

Typical UK practice: Prestwick’s met system make is not public. Integrated systems of this kind (for example Vaisala AviMet AWOS) are typical in the UK.

// Through the eras

Met display in each era of the Prestwick tower
Era	Status	Notes
1930s–40s	Typical UK practice	A wind-direction repeater, a barometer and reports from the met office are typical of a wartime watch office.
1950s–60s	Typical UK practice	Analogue wind dials and a precision barometer are typical.
1980s–90s	Typical UK practice	Digital LED readouts for wind and pressure are typical.
Modern	Typical UK practice	An integrated met display is required (CAP 670); Prestwick’s system make is not public.