What does it mean when there is no ceiling or "CLR" in an airport METAR? Here's the current METAR at KFLG:


  KFLG 210657Z AUTO 21010KT 3/4SM -SN BR VV010 M07/M09 A2961 RMK AO2
  SLP044 P0003 T10721094 410331178


It doesn't have anything about cloud layers or "CLR", but it shows what the vertical visibility is. Why doesn't it have information about the cloud layers?
Vertical Visibility with a number means that cloud layers cannot be determined because of haze, fog or mist, instead it's a measure of how far up the weather station can see. Because its sensors cannot penetrate further the station cannot tell you whether there's clouds above that level or not, but it does say in this case that there are no clouds below 1000 feet. 

You may see VV/// sometimes, this means cloud cannot be measured. If fog, mist or haze and poor visibility is reported as well then it's likely that the fog is so thick the sensors cannot penetrate it, if on the other hand visibility is good with no fog or haze it's likely a sensor malfunction.