Why is high air pressure associated with bad weather and low air pressure is associated with good weather?

Answer 1

Low pressure areas form when an airmass warms, either from being over a warm land or ocean surface, or from being warmed by condensation of water vapour in large rain or snow systems. The warming causes the air layer to expand upward, becoming slightly thicker. This expansion then causes air in the upper troposphere to flow away, leaving less mass, and so less weight (pressure) at the surface. The lower pressure air at the surface then causes higher pressure air around it to flow toward lower pressure, but as it does, the rotation of the Earth turns the wind to the right, resulting in the counter-clockwise wind flow around low pressure (in the Northern Hemisphere...it flows in the opposite direction in the Southern Hemisphere).

High pressure areas form when an airmass cools over a cool land or ocean surface. The cooling causes the air layer to shrink, becoming slightly thinner. This shrinkage then causes surrounding air in the upper troposphere to fill up the extra space. The added weight of the extra air causes higher pressure at the surface. The higher pressure air at the surface then tries to flow outward toward lower pressure, but as it does, the rotation of the Earth turns the wind to the right, resulting in the clockwise wind flow around the high pressure (in the Northern Hemisphere...it flows in the opposite direction in the Southern Hemisphere).

Answer 2

From his vantage point in England in 1848, Rev. Dr. Brewer wrote in his A Guide to the Scientific Knowledge of Things Familiar the following about the relation of pressure to weather:

The FALL of the barometer (decreasing pressure)

• In very hot weather, the fall of the barometer denotes thunder. Otherwise, the sudden falling of the barometer denotes high wind.
• In frosty weather, the fall of the barometer denotes thaw.
• If wet weather happens soon after the fall of the barometer, expect but little of it.
• In wet weather if the barometer falls expect much wet.
• In fair weather, if the barometer falls much and remains low, expect much wet in a few days, and probably wind.
• The barometer sinks lowest of all for wind and rain together; next to that wind, (except it be an east or north-east wind).

The RISE of the barometer (increasing pressure)

• In winter, the rise of the barometer presages frost.
• In frosty weather, the rise of the barometer presages snow.
• If fair weather happens soon after the rise of the barometer, expect but little of it.
• In wet weather, if the Mercury rises high and remains so, expect continued fine weather in a day or two.
• In wet weather, if the mercury rises suddenly very high, fine weather will not last long.
• The barometer rises highest of all for north and east winds; for all other winds it sinks.

The barometer UNSETTLED (unsteady pressure)

• If the motion of the mercury be unsettled, expect unsettled weather.
• If it stands at "MUCH RAIN" and rises to "CHANGEABLE" expect fair weather of short continuance.
• If it stands at "FAIR" and falls to "CHANGEABLE", expect foul weather.
• Its motion upwards, indicates the approach of fine weather; its motion downwards, indicates the approach of foul weather.

These pressure observations hold true for many other locations as well but not all of them. Storms that occur in England, located near the end of the Gulf Stream, bring large pressure changes. In the United States, the largest pressure changes associated with storms will generally occur in Alaska and northern half of the continental U.S. In the tropics, except for tropical cyclones, there is very little day-to-day pressure change and none of the rules apply.

Answer 3

High pressure is typically associated with fair weather.

Answer 4

BECAUSE it has to do with percepitation

Answer 5

Yes