Altostratus is a mid-level cloud identified by its height, between 6,000 feet and 18,000 feet, and its generally smooth layered appearance. Sometimes the cloud has a diffuse base like shown here. In this case the Sun is dimly visible but altostratus often obscures the Sun's disk. Altostratus is not a precipitating cloud. This cloud formed in a layer of gentle upward motion that developed in advance of a winter storm moving eastward from the Rockies. The storm emerged on the Plains as a low center in Kansas and moved east. Heavy snow fell in parts of southern Minnesota and northeastern Iowa.
The map below was plotted from observations taken at 11:00 a.m. CDT on March 23, 2018. At that time the low center was reorganizing from Wyoming into northwestern Kansas. Notice the closed oval isobar enclosing eastern Wyoming, the Nebraska Panhandle, northeastern Colorado, and far western Kansas. By early evening the low center had formed over northwestern Kansas. The altostratus over Fort Dodge, Iowa was in a band that extended from northwest into southeast Iowa. The bases were above 12,000 feet. Lower clouds were located over western North Dakota southeastward to St. Louis. The ceiling at Des Moines, Iowa was at 7,000 feet (C70)* while ceilings in western North Dakota and eastern South Dakota were below 3,000 feet (C27, C28, C25)*.
The ceilings are plotted on the station model. Red indicates ceilings below 3,000 feet. Clouds above 12,000 feet are not plotted.