High altostratus clouds and night flying conditions prevented him from making any visual contact.

Altostratus cloud: Thicker than cirrostratus; sun's disc just visible.

Often, when an altostratus cloud thickens and descends into lower altitudes, it will become nimbostratus.

If the precipitation increases in persistence and intensity, the altostratus cloud may thicken into nimbostratus.

They also can occur under altostratus cloud preceeding a warm or occluded front, when cumulus usually lose vertical development as the sun's heat decreases.

Nimbostratus, Stratus cloud, Altostratus cloud and stratocumulus clouds all have a smooth gray appearance.

A sheet of altostratus cloud often is seen lower down in a cumulonimbus cloud, this is known as a velum cloud.

On this day, however, the sky, layered with thin altostratus clouds and smog, appeared to reflect human suffering and failed to awaken in Claude visions of paradise.

Nimbostratus will occur along a warm front where the slowly rising warm air mass creates nimbostratus along with shallower stratus clouds producing less rain, these clouds being preceded by higher-level clouds such as cirrostratus and altostratus clouds.

Cumulonimbus velum (Cb vel) (from the Latin cumulonimbus, "column-rain" + velum, "veil") is a cumulonimbus cloud with a small layer of altostratus cloud wrapped around its mid area, representing an area of humid stable air created as a result of the growth of the parent cumulonimbus.