This was found using a long tube filled with mercury, which is what the first barometers were.
When storms draw near, atmospheric pressure aka barometric pressure drops, due to air rising upward.
The air rises because that is what air naturally wants to do, which is go upwards.
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These clouds lead to storms.
Thus, theres less air pressing down, meaning more air can rise.
That rising air is, as noted above, what leads to clouds and rain.
Generally speaking, the lower the air pressure, the more likely it is to rain.
On a barometer, low air pressure will cause the fluid inside to rise higher in the tube.
Different Types of Barometers
Barometers come in various types.
These are the simplest form of barometer, but also tend to be fairly inaccurate.
Reading these is as easy as seeing where the fluid is inside the tube.
If its high, expect warmth and sunshine.
As it goes lower, you could anticipate storms or clouds.
The lower it goes, the more serious the storm.
The higher, the hotter and drier the air will be.
The resistance is then measured and displayed on an output of the electronic barometer.
In a Fluid Barometer
Fluid barometers are hard to find, and are typically antiques.
These can work one of two ways.
Should it begin to rise, the air pressure is lessening, leading to storms.
Others will have a tube that goes up and down, but then loops upward at the bottom.
When it says the pressure is dropping, storms are coming.
When it says its rising, more heat is likely.
