Weather & ATIS

090 CommunicationsChapter 6

Weather information sources

Key fact

In the air, ATC, ATIS, and VOLMET may give weather information. Broadcast on VHF and UHF.

ATIS

Key fact

ATIS provides routine information as a repetitive broadcast on discrete VHF and/or VOR. Usually updated every 30 minutes. D-ATIS is the datalink Automatic Terminal Information Service.

Runway visual range (RVR)

Key fact

RVR is reported when prevailing visibility is under 1,500 m. Format example: R27R/1500U.

Trend values after the number:

Code	Meaning
U	Increasing RVR
N	Neutral
D	Decreasing RVR

Key fact

Wind shear phraseology: WS ALL RWY (on all runways) or WS RWY27L (on a specific runway).

Braking action codes

Coefficient	Braking action	Code
over 0.4	Good	5
0.39 to 0.36	Medium to good	4
0.35 to 0.30	Medium	3
0.29 to 0.26	Medium to poor	2
under 0.25	Poor	1
—	Unreliable (slush)	9

METAR format

Key fact

Format is location, then date and time of issue (DDHHMM) — e.g. LEJR 032330Z. Visibility in km if over 5,000 m; otherwise 4 digits in metres. Wind in degrees true and m/s or kts. “Hear it magnetic, see it true.” Temperature in °C.

Key fact

METAR is updated when wind direction changes over 60° or speed increases over 10 kts. Also updated with MET REPORT SPECIALs.

Definition — CAVOK

Ceiling and Visibility OK — visibility 10 km+, no cloud below 5,000 ft or MSA, no CBs/TCU reported, no significant weather.

Cloud amount (oktas)

Oktas	Description
1–2	FEW
3–4	SCATTERED
5–7	BROKEN
8 (100%)	OVERCAST

VOLMET

Key fact

VOLMET gives weather for multiple airports in flight. Includes TAFs, SIGMETs, and METARs.

Exam trap

Wind in METAR is true; wind in ATIS/verbal reports is often magnetic. Remember: “Hear it magnetic, see it true.”