sheet-like and nearly transparent
Cirrostratus are sheet-like clouds composed of ice crystals.
Though cirrostratus can cover the entire sky and be up
to several thousand feet deep, they are relatively transparent, as the
sun or the moon can be easily seen through them. Sometimes the only
indication of their presence is given by an observed
halo around the sun or moon
Halos result from
of light by the cloud's ice crystals.
|These high level clouds typically form when
a broad layer of air is lifted to
Lifting Condensation Level
Cirrostratus clouds, however, tend to thicken as a
warm front approaches,
signifying an increased production of ice crystals. As a result, the
is no longer seen and the sun (or moon by night) becomes less visible.
During sunrise and sunset,
these clouds can appear in a magnificent array
of colors as
unscattered components of sunlight (red, yellow, and orange) are reflected by
the underside of the clouds.
The criss-cross pattern of cirrus
streaks is commonly seen before an approaching
The cirrus streaks were aligned
in a southwest to northeast direction, indicative of the advancing
warmer air at higher levels. Lower on the horizon, thickening cirrostratus
clouds effectively hide the sun, signifying changing weather ahead.
With time, these clouds will thicken into
altostratus and eventually into the lower and more dense
clouds as the warm front
gets closer and closer.