Weather Terms in Radio (RTF)

Weather terms in radio (RTF)

In radio traffic, weather information — from ATIS, ATC, AFIS or in reply to a weather query — is transmitted in standardised ICAO format. The PPL pilot must understand and correctly interpret these terms.

Wind

Format: direction / speed / gusts

Examples:

• "Wind 270 degrees 10 knots" = wind from 270° (west) at 10 kt.
• "Wind 180 degrees 15 knots, gusting 25" = wind from south at 15 kt, gusts to 25 kt.
• "Wind variable 5 knots" = light wind, varying direction.
• "Wind 270 degrees 15 knots, varying between 240 and 300" = mean direction 270°, variation 240–300°.

Magnetic vs true:

• In radio: wind is given magnetic (ATC reference relative to runway direction).
• In METARs: wind is given true.
• For VFR approach: runway direction is magnetic — no conflict.

Visibility

Format: visibility in metres or kilometres, sometimes with direction.

Examples:

• "Visibility 10 kilometres" = 10 km in all directions.
• "Visibility 5 kilometres" = 5 km.
• "Visibility 2 000 metres in showers" = 2 km in showers.
• "Visibility 8 kilometres, to the north 4 000 metres in rain" = 8 km generally, 4 km to the north in rain.

Minimum visibilities for PPL VFR:

• Class G below 3 000 ft AMSL at 140 kt IAS: 1 500 m (clouds in sight of ground).
• Above 3 000 ft AMSL: 5 km.
• VFR Night: 5 km.

Runway Visual Range (RVR)

Definition: visibility along the runway, measured by sensors — typically relevant for IFR approaches.

Format: "runway / value / trend"

Examples:

• "RVR runway 25 left 1 500 metres" = RVR runway 25 L: 1 500 m.
• "RVR runway 25 1 200 metres downward" = 1 200 m, falling.
• "RVR runway 25 above 2 000 metres" = > 2 000 m.

Trend symbols in METAR/RVR:

• U (UP) = increasing,
• D (DOWN) = decreasing,
• N (NO CHANGE) = unchanged.

Key thresholds:

• RVR < 550 m: no PPL VFR.
• RVR < 200 m: only Cat IIIa IFR approaches.

Cloud height and ceiling

Definition of ceiling: height of the lowest cloud layer AGL that covers more than half the sky (BKN or OVC).

Radio format: "ceiling [value] feet" or "cloud base [value] feet".

Examples:

• "Ceiling 1 500 feet broken" = 1 500 ft AGL, BKN deck.
• "Cloud base 800 feet overcast" = OVC at 800 ft AGL.
• "Sky clear" = no clouds.
• "Scattered 3 000 feet" = SCT at 3 000 ft.

Coverage (oktas):

• SKC / CLR — clear (0 oktas).
• FEW — few (1–2 oktas).
• SCT — scattered (3–4 oktas).
• BKN — broken (5–7 oktas).
• OVC — overcast (8 oktas).

Weather phenomena

Standardised ICAO codes (also in METAR):

Intensity prefixes:

• − = light (e.g. −RA = light rain),
• (no prefix) = moderate,
• + = heavy (e.g. +TS = heavy thunderstorm).

Modifiers:

• SH = shower (e.g. SHRA = rain shower),
• TS = thunderstorm (e.g. TSRA = thunderstorm with rain),
• FZ = freezing (e.g. FZRA = freezing rain, FZFG = freezing fog).

Runway state

In radio and SNOWTAM:

Temperature and dew point

Format: "temperature [value] degrees, dew point [value] degrees".

Examples:

• "Temperature 15, dew point 10" = T 15 °C, Td 10 °C.
• In METAR notation: M = minus, e.g. "M05 / M08" = T −5 °C, Td −8 °C.

Spread (T − Td) rule of thumb:

• < 3 °C: high probability of fog formation.
• 0 °C: already saturated, fog/precipitation.
• Larger: stable, clear weather.

QNH and QFE on radio

Format: "QNH [value] hectopascals" or "QFE [value] hectopascals".

Examples:

• "QNH 1018" = QNH 1018 hPa (typical cruise weather).
• "QFE 985" = QFE 985 hPa (set altimeter to zero on field).

With US ATC: often in inches of mercury (inHg) — "altimeter 29.92" = QNH 29.92 inHg = 1013.25 hPa.

TREND forecasts

In ATIS or METAR with TREND extension:

Example: "NOSIG" at the end of an ATIS = weather remains stable.

Radio pronunciation

Important: some terms are spoken, not spelled:

• "METAR" — spoken as "M-E-T-A-R" (typically letter-by-letter due to brevity).
• "TAF" — pronounced "Taf".
• "SIGMET" — pronounced "Sigmet".
• Q-codes: spell letter-by-letter ("Quebec November Hotel" for QNH).