What is the relationship between temperature, dew point and the formation of clouds? What can you infer from the temperature / dew point values in this METAR?


  EGJG 121630Z 09012KT 9999 SCT006 15/14 Q1015


I understand the temperature is 15 degrees and the dew point is 14, and I found this:


  The temperature / dew point spread is low, so the risk of cloud
  forming is high especially if the temperature falls.


Why is the risk of clouds forming high, especially if the temperature is falling?
The dew point is the temperature at which condensation (a cloud) forms.

If the dew point is the same as the temperature on the ground, then there will be fog.

The temperature usually decreases as the altitude increases. This is called the lapse rate. In general, the closer the dew point is to the ground temperature, the lower the cloud ceiling will be.