What You Need to Know:
Name(s): Cirrus Uncinus (‘curly hooks’), Mare’s Tails
Altitude of Formation: 7000m and above
Temperature of Formation: -50°C
Signals: Warm or occluded fronts and some sort of precipitation
Meaning of the Name: Latin for ‘Curly Hooks’
Elaborated, More Comprehensive Information
Cirrus uncinus appearing in the sky is an indicator of precipitation from a warm or occluded front in around 12 hours.
The high-level clouds are composed of (like all cirrus) water droplets which cool into ice crystals at around -40 to -50°C. The cooling into ice crystals are evident in the hooks in the mare’s tails. This is the upward motion of the water droplets causing them to cool faster or slower than it cools by the the downward motion. The direction of the hooks are also depicted by the wind shear, when wind shear is positive (when the momentum of the headwind is increased or the tailwind is decreased), the hook curves downward, vice versa for the negative wind shear).