Graphic area forecast (GFA)
Picture of expected weather at or below 24,000 ft ASL over a region, for pre-flight planning.
Issue (TC AIM MET 4.2): four times a day, about 30 min before valid time.
| Issued (Z) | Valid (Z) |
|---|---|
| ~2330 | 0000 |
| ~0530 | 0600 |
| ~1130 | 1200 |
| ~1730 | 1800 |
Basics:
| Item | Value | Cite |
|---|---|---|
| Coverage | 7 regions | TC AIM MET 4.3 |
| Validity | 12 hours | TC AIM MET 1.3.6 |
| Charts per issue | 6 (2 chart types x 3 valid times: start, +6 h, +12 h) | TC AIM MET 4.2 |
- New issue replaces previous (TC AIM MET 3.1, table).
Two chart types:
| Chart | Shows |
|---|---|
| Clouds and weather | Cloud bases and tops, visibility, weather, obstructions to vision |
| Icing, turbulence and freezing level | See the GFA icing and turbulence chart symbols lesson |
- Fronts and pressure systems drawn on both charts (TC AIM MET 4.11, 4.12).
Units (TC AIM MET 4.4):
| Quantity | Unit |
|---|---|
| Height | hundreds of ft ASL |
| Speed | knots |
| Visibility | SM |
| Time | UTC |
Symbols (TC AIM MET 4.5, 4.8):
- Standard meteorological abbreviations only, as on significant weather prognostic charts.
- Colour charts: TS and PL red.
Interpolate between valid times (TC AIM MET 4.2):
- Each 5 kt of forecast motion = feature moves 30 NM in 6 h (6 NM per kt).
References
- TC AIM MET 4.0 (Graphic Area Forecast)