Low Pressure and High Pressure Systems
Low pressure occurs where warm air ascends and cools down allowing clouds to form which is the reason why weather is almost always unsettled when the weather is dominated by Low pressure systems. High pressure is where cool dry air descends warming as it does so and suppressing cloud formation leading to dry settled conditions. As you can see air flows between the two systems. Low pressure systems have weather fronts associated with them while High pressure systems don’t. See also Cyclogenesis and Explosive Cyclogenesis.
Low pressure occurs where warm air ascends and cools down allowing clouds to form which is the reason why weather is almost always unsettled when the weather is dominated by Low pressure systems. High pressure is where cool dry air descends warming as it does so and suppressing cloud formation leading to dry settled conditions. As you can see air flows between the two systems. Low pressure systems have weather fronts associated with them while High pressure systems don’t. See also Cyclogenesis and Explosive Cyclogenesis.
Fax Charts Showing Low pressure and High pressure
Here you see a fax chart showing High pressure and Low pressure systems. Note the cold fronts, warm fronts and Occluded fronts on the fax chart. Low pressure systems are indicated by L and High pressure by H.
Cyclogenesis and Explosive Cyclogenesis (Bomb)
Cyclogenesis refers to the formation of low pressure systems. All Atlantic Depression, Low pressure systems are a form of Cyclogenesis. These ranging from wave depressions to modification of ex hurricanes. Cyclolysis refers to when the low pressure weakens soon after the cold air reaches the centre.
Col
A Col is the area of slack pressure between two low pressure systems and two high pressure systems. The weather within a col is generally quiet any showers will be slow moving due to light winds. The light winds also allow formation of fog or mist and winter frosty conditions.
Atmospheric Pressure or Air Pressure
Atmospheric Pressure is the force per unit of on a surface by the weight of air above it. This is commonly measured in millibars mb or Inches. So you may see a Low pressure or a High pressure system with the number 1002 next to it. This will be the value in millibars mb. The same value would be 29.59 in.