Wind shear: WS group, PIREP guideline & detection
TAF WS group (TC AIM MET 7.3):
- Forecasts low-level, non-convective wind shear (excludes thunderstorm-driven shear).
- Forecaster has strong evidence it will affect aircraft within 1,500 ft AGL over the aerodrome.
- Low-level shear commonly from passing fronts, thunderstorms, temperature inversions, strong upper-level winds (FAA PHAK, line 14363). WS group covers only the non-convective ones.
WS011/27050KT
| Part | Meaning |
|---|---|
011 |
Top of shear layer, hundreds of ft AGL (011 = 1,100 ft AGL) |
270 |
Wind direction at that height, true |
50 |
Wind speed at that height, kt |
- Decode: shear from surface to 1,100 ft AGL; wind at top 270° true at 50 kt.
METAR WS group (TC AIM MET 8.2):
WS RWY06orWS ALL RWY: low-level wind shear within 1,500 ft AGL along runway takeoff or approach path.- Parallel runways: append
L,CorR.
Significant shear: PIREP guideline (TC AIM MET 7.3(d)):
- A pilot report of an IAS gain or loss of 20 kt or more within 1,500 ft AGL indicates significant low-level wind shear, justifying a WS group.
Detection and reporting (TC AIM MET 2.3, 8.4.4 Table 8.3):
| Source | Wind shear |
|---|---|
| Ground sensors | None in Canada; shear is normally deduced only from PIREPs |
| AWOS | Never reports it (no capability) |
| Human observer | Reports known wind shear in the lower layers |
Shear vs turbulence (TC AIM MET 7.3):
| Hazard | Signature |
|---|---|
| Wind shear | Rapid gain or, worse, loss of airspeed |
| Turbulence | Erratic changes in altitude or attitude |
- WS group is not a turbulence report.
Trap: reading WS height as feet AMSL, or missing the x100 scale (011 is 1,100 ft, not 11 or 110 ft); a smaller IAS change than 20 kt, or a different altitude than 1,500 ft AGL, does not qualify; expecting ground wind-shear sensors or AWOS to show wind shear.
References
- TC AIM MET 7.3 (low-level wind shear group)
- TC AIM MET 7.3(a)-(d) (significant wind shear guidelines)
- TC AIM MET 8.2 (METAR WS group)
- TC AIM MET 2.3
- TC AIM MET 8.4.4 (Table 8.3 wind shear row)
- FAA PHAK (wind shear causes, line 14363)