Gust fronts and storm turbulence
Gust front: leading edge of storm outflow. Two marker cloud types (AWH 22.6):
| Cloud | Shape | Attachment |
|---|---|---|
| Roll cloud | Tube | Completely detached from storm base |
| Shelf cloud | Wedge | Attached to parent cloud above |
- Can outrun its rain by up to 15 mi.
- Causes rapid surface wind shift.
Turbulence: present in every thunderstorm.
- Strongest inside cloud, in shear zone between updraft and downdraft. Not spread evenly through rain.
- Gust loads there can stall aircraft at manoeuvring speed, or structurally damage it at cruise speed (AWH 19.2.1.1).
- Not confined to cloud:
- Shear turbulence several thousand feet above a severe storm, outside cloud (PHAK ch.12).
- Severe turbulence may extend up to 20 NM from severe thunderstorms (TC AIM AIR 2.7.1).
Trap: confusing roll cloud (detached) with shelf cloud (attached).
References
- FAA-H-8083-28_aviation-weather-handbook.md 22.6 (Thunderstorm Terminology)
- FAA-H-8083-28_aviation-weather-handbook.md 19.2.1.1 (Thunderstorms)
- FAA-H-8083-25_PHAK ch.12 (Turbulence)
- TC AIM AIR 2.7.1 (flight near thunderstorms: general)