GFA layout, comments box & corrections
Every GFA chart (clouds-and-weather panel, icing/turbulence/freezing-level panel) has the same four parts (TC AIM MET 4.6):
| Part | Position | Holds |
|---|---|---|
| Weather information section (the picture) | Left, most of chart | Forecast picture |
| Title box | Right side, top | Chart name, issuer, region, type, issue and valid times |
| Legend box | Right side, middle | Symbols used on that chart, nautical mile scale bar |
| Comments box | Right side, bottom | Forecaster's supplementary notes (below) |
Title box example: GFACN33 CWAO REGION ONTARIO-QUEBEC
- GFACN33 = chart name
- CWAO = Montreal forecast office (issuer, four-letter identifier)
- Ontario-Quebec = GFA region name
- Chart type = clouds and weather
Comments box: forecaster's notes too fiddly to draw or that would clutter the chart (TC AIM MET 4.9).
| Phrase (printed on every issue) | Meaning |
|---|---|
HGT ASL UNLESS NOTED |
Heights ASL unless noted |
CB TCU AND ACC IMPLY SIG TURB AND ICE |
CB, TCU, ACC imply significant turbulence and icing |
CB IMPLIES L LVL WS |
CB implies low-level wind shear |
- Lettered areas (A, B, C...) match the same-lettered area on the main chart.
- No letter: applies everywhere else on the chart.
- 12-hour IFR outlook:
- On the final (12-hour) clouds-and-weather chart only, lower part of the comments box.
- Covers 12 hours beyond the chart's 12-hour validity.
NIL SIG WX= no organized IFR expected in that period.
Corrections (TC AIM MET 4.14): a reissued GFA marks a correction on the first line of the title box.
| Correction | Code |
|---|---|
| First | CCA |
| Second | CCB |
| Third | CCC |
- Issued for:
- unforecast weather below AIRMET criteria that the forecaster judges should be shown
- forecast weather that fails to occur (removed from the chart)
- a significant error that would cause a hazardous misreading
- The comments box explains what changed.
Trap: inventing a fifth box, or calling a routine new issue a correction (no CCA, CCB or CCC).
References
- TC AIM MET 4.6 (GFA layout, Table 4.1)
- TC AIM MET 4.7 (title box, Table 4.2)
- TC AIM MET 4.8 (legend box)
- TC AIM MET 4.9 (comments box)
- TC AIM MET 4.11 (comments box location)
- TC AIM MET 4.14 (GFA corrections)