http://www.stormcam.org/barometric-weather/
How are barometric readings analyzed?
How are barometric readings interpreted with regards to weather patterns and/or changes?
Low pressure indicates a storm system, while high pressure indicates fair weather. The change in barometric pressure indicates which way the weahter is trending. Falling pressure means that a storm may be on the way in, while rising pressure means you can expect clear skies soon.
The most severe cyclones (typhoons, hurricanes, etc.) may have pressures as low as 900 mbar or 26 inches of mercury. A more typical storm on land has pressures in the vicinity of 980 mbar or 29 in Hg. A typical nice day has pressure slightly above 1000 mbar, or about 30 in Hg. The highest atmospheric pressure ever measured on the surface of the Earth was over 1080 mbar, or 32 in Hg, but that’s quite exceptional.
Weather Barometers : Understanding Barometer Readings