As cirrostratus clouds thicken they form into Altostratus clouds. They are grey or blue and contain very few features.
Spreading over a large area forming mid level featurless clouds. Dull but not too thick it is likely that the sun will appear if only briefly and obscured. Sometimes effects effects such as coronas and iridescence accompany these clouds.
What's in a name?
Alto - high or on high. From above. Stratus - to spread out, extend, flatten, layer.
How was it made?
When Cirrostratus clouds descends from a higher level the water and icecrystals in the cloud thickern and form these mostly featurless clouds.
What weather will you have if these are overhead?
Most likely its dry with these overhead but as they thicken they can form nimbostratus clouds which are rain bearing so Altostratus clouds are often a sign that the weather is going to change.
How high is it?
Anywhere from 2,100m (6,500ft) up to 7,000m (20,000 ft).
The outcome for you.
Shadowless day which could become wetter, worth getting the umbrella ready just in case.
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