Aerodrome weather-observation station types
CFS labels each aerodrome's weather service by what produces it, not what it reports.
| Label | Produced by | Reports | Cite |
|---|---|---|---|
| METAR | Qualified human observer | Full hourly report (plus SPECI as needed) | MET 1.2.3(a) |
| METAR AUTO | AWOS meeting complete METAR AUTO standard (NAV CANADA or DND) | Same full report | MET 1.2.3(b) |
| LWIS (Limited Weather Information System) | Automated | Hourly, only 4 elements: wind, temperature, dew point, altimeter setting. No cloud, no visibility | MET 1.2.3(c) |
| AUTO | Automated, below even LWIS standard | Variable, non-standard subset of elements | MET 1.2.3(d) |
| VFR weather station | - | Local VFR use only | MET 1.2.4.2 |
| LAWO | Airport controllers, from tower cab | Visual observation of prevailing tower visibility and tower ceiling | MET 1.2.3(i) |
Per-label rules:
- LWIS:
- Still carried on the main network (MET 1.2.3, paragraph after item (i)).
- Transmits data to ATS facilities on the hour, separately from the minute-by-minute feed to its affiliated VGSS and VHF transmitter (TC AIM MET 1.2.5.2).
- Coded like:
LWIS CYXP 221700Z AUTO 25010G15KT 03/M02 A3017(MET 8.4.2).
- AUTO:
- Not on the main telecommunications network. Call aerodrome operator for specifics (MET 1.2.3(d)).
- Covers all other automated reports that have demonstrated TC compliance and are usable for IFR flight. Performance varies widely (MET 1.2.6).
- Fewer than the four LWIS elements = AUTO. Exception: DND High Arctic stations that omit dew point (MET 1.2.5.2).
- Automated system unable to report all elements needed for METAR AUTO/SPECI AUTO (and any TAF it supports): AUTO or LWIS.
- Local "AWOS" not supporting METAR AUTO/SPECI AUTO: listed as AUTO in CFS (MET 1.2.4.1).
- VFR weather station:
- Not usable for IFR (altimeter/wind do not meet IFR standards).
- Not permitted at an aerodrome with an instrument approach procedure.
- Not published in the CFS (MET 1.2.4.2).
- LAWO: made to support local flight operations. Not intended for transmission, distribution, or use outside the control zone (MET 1.2.3(i)).
- METAR AUTO (MET 1.2.5.1):
- May support a TAF at associated aerodrome.
- Minimum observed and reported: wind, altimeter setting (from multiple sensors as a failsafe), air temperature, dew point, visibility, cloud height, sky coverage, precipitation occurrence/type/intensity, fog and related obstructions, thunderstorm detection, icing, plus RVR when required.
US vs Canadian terms (MET 1.2.4.1):
| US term | Canadian equivalent |
|---|---|
| ASOS | METAR AUTO |
| AWOS | LWIS |
Representative observation: only if taken within 1.6 NM (3 km) of runway complex centre (MET 7.2).
Location indicator (MET 8.4.4, Table 8.3):
| Report type | Indicator |
|---|---|
| Normal | Aerodrome's own 4-letter identifier (CY..) |
| Human-observed, observer not at aerodrome (station beyond 1.6 NM (3 km) from runway complex's geometric centre) | Prefix CW instead of CY |
| NAV CANADA METAR AUTO | No difference |
- Example: Cartwright aerodrome is
CYCA, its weather report isCWCA.
Trap: LWIS = defined 4-element hourly report on main network; AUTO = non-standard leftover subset, not on it, so plain "AUTO" is the one to phone the operator about.
References
- TC AIM MET 1.2.3
- TC AIM MET 1.2.4.1
- TC AIM MET 1.2.4.2
- TC AIM MET 7.2
- TC AIM MET 8.4.4 (Table 8.3)