You set up a fire at the end of a long day hiking, or driving to your campsite, and you gather around to have a nice relaxing evening. However, you soon notice that the smoke is hanging lower than usual, and doesn't seem to be rising straight off into the sky.
What does this mean?
It means there might be rain on the way! As I've mentioned, changing weather can often be measure by changing air pressure, as the two go hand in hand. When the air pressure decreases, low pressure (which brings clouds and sometimes precipitation) is on the way. Increasing pressure means high pressure areas are on the way, which often means fine, clear days.
So, how does that affect your fire?
If the smoke is hanging low to the ground:
A low pressure system is on the way, and rain may come! This happens because of the temperature changes that occur when low pressure systems move in, keeping the smoke from rising into the air.
If the smoke is rising in a straight, vertical column:
A high pressure area is moving in; fair weather should grace your future!
And now you know! So, next time you notice something amiss with your campfire smoke, be smart and make preparations for the change in weather that is sure to happen in the coming days!