As with those sayings related to humidity or clouds, much of the weather lore that is based on changes in air pressure or the wind can accurately predict the weather. Air pressure and wind are two weather indicators that can be used to determine future weather conditions over the short term.
“When the wind is out of the east,
‘Tis neither good for man nor beast.”
Easterly winds usually indicate an approaching weather front or low pressure area. Low pressure generally brings bad weather. Remember that wind circulates around a high pressure cell in a clockwise direction. So if the wind is out of the east, a “high” that came from the west has already passed you by, or is currently passing by on the north. A low pressure system is sure to follow since highs and lows usually tend to alternate in progression.
Lore About Air Pressure
Moderator: S2k Moderators
Forum rules
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K.
-
Rob-TheStormChaser
AIR PRESSURE
The air is a fluid. As with any other fluid, it has internal pressure due to the force of Earth’s gravity. Normally, the weight of the air is 14.7 pounds per square inch measured at sea level. It gets lower with increasing altitude.
Air pressure is typically measured by reading how high a column of mercury can be suspended in a glass tube by the pressure of the air against the mercury in a cup in which the tube has been inverted. At sea level, this is normally 29.92 inches high, or about 760 millimeters. We call this normal atmospheric pressure.
Pressure differences are caused by the uneven heating of the surface of the earth by the sun. An area that is receiving a lot of solar radiation will become wanner, and the air volume will expand. As air becomes warmer, its molecules move faster and therefore, bump each other farther apart. This increases the volume of the air. A volume of warm air will contain fewer air molecules than an equal volume of cold air.
When the weight of the air over one region of earth becomes lower than the surrounding area, the parcel of air in that region begins to rise, being pushed upward by the higher pressure of the surrounding air. Air under low pressure, therefore, rises.
As air rises, it cools. As has already been stated, cooler air can hold less moisture. So if the rising air reaches an altitude where it is too cool to hold the amount of moisture it had on the ground, that moisture condenses out as clouds. Thus, low pressure areas produce cloudy and rainy weather.
High pressure areas are produced by heavy, sinking air. They are characterized by clear weather. An area of high pressure is sometimes call a high pressure cell, or simply, a “high.” Low pressure cells are usually just called “lows.”
The instrument used to measure air pressure is called a barometer. The change in the pressure, and how fast it is changing, is more indicative of the weather than the pressure itself. Rapidly falling pressure almost always means an approaching storm system. Rapidly rising pressure almost always means clearing and cooler weather is ahead.
More to follow
The air is a fluid. As with any other fluid, it has internal pressure due to the force of Earth’s gravity. Normally, the weight of the air is 14.7 pounds per square inch measured at sea level. It gets lower with increasing altitude.
Air pressure is typically measured by reading how high a column of mercury can be suspended in a glass tube by the pressure of the air against the mercury in a cup in which the tube has been inverted. At sea level, this is normally 29.92 inches high, or about 760 millimeters. We call this normal atmospheric pressure.
Pressure differences are caused by the uneven heating of the surface of the earth by the sun. An area that is receiving a lot of solar radiation will become wanner, and the air volume will expand. As air becomes warmer, its molecules move faster and therefore, bump each other farther apart. This increases the volume of the air. A volume of warm air will contain fewer air molecules than an equal volume of cold air.
When the weight of the air over one region of earth becomes lower than the surrounding area, the parcel of air in that region begins to rise, being pushed upward by the higher pressure of the surrounding air. Air under low pressure, therefore, rises.
As air rises, it cools. As has already been stated, cooler air can hold less moisture. So if the rising air reaches an altitude where it is too cool to hold the amount of moisture it had on the ground, that moisture condenses out as clouds. Thus, low pressure areas produce cloudy and rainy weather.
High pressure areas are produced by heavy, sinking air. They are characterized by clear weather. An area of high pressure is sometimes call a high pressure cell, or simply, a “high.” Low pressure cells are usually just called “lows.”
The instrument used to measure air pressure is called a barometer. The change in the pressure, and how fast it is changing, is more indicative of the weather than the pressure itself. Rapidly falling pressure almost always means an approaching storm system. Rapidly rising pressure almost always means clearing and cooler weather is ahead.
More to follow
0 likes
-
Rob-TheStormChaser
“When the wind is in the north. The skillful fisher goes not forth;
When the wind is in the cast, ‘Tis good for neither man nor beast;
When the wind is in the south, It blows the flies in the fish’s mouth;
But when the wind is in the west, There it is the very best.”
“Fish bite least
With wind in the east.”
In the U.S. the prevailing winds are from the west, northwest, or southwest. As a general rule, winds coming from a westerly direction signifies good weather. It is only a matter of conjecture, however, if fish react to the direction of the wind.
When the wind is in the cast, ‘Tis good for neither man nor beast;
When the wind is in the south, It blows the flies in the fish’s mouth;
But when the wind is in the west, There it is the very best.”
“Fish bite least
With wind in the east.”
In the U.S. the prevailing winds are from the west, northwest, or southwest. As a general rule, winds coming from a westerly direction signifies good weather. It is only a matter of conjecture, however, if fish react to the direction of the wind.
0 likes
-
Rob-TheStormChaser
“When the wind backs; and the weather glass falls
Prepare yourself for gales and squalls.”
A backing wind is one which changes direction in a counterclockwise manner—usually starting in the west, then changing to the southwest, south, and then southeast. A backing wind indicates the approach of a low pressure cell from the southwest.
Prepare yourself for gales and squalls.”
A backing wind is one which changes direction in a counterclockwise manner—usually starting in the west, then changing to the southwest, south, and then southeast. A backing wind indicates the approach of a low pressure cell from the southwest.
0 likes
-
Rob-TheStormChaser
The “weather glass” was an early term for a crude barometer. When the weather glass falls, the atmospheric pressure is lowering, signaling the approach of a storm system.
A similar rhyme goes like this:
“When the glass falls low,
Prepare for a blow;
When it rises high.
Let all your kites fly.”
Again, the “glass” referred to here represents a barometer, which measures air pressure. High pressure means fair weather; low pressure indicates rain or storms.
A similar rhyme goes like this:
“When the glass falls low,
Prepare for a blow;
When it rises high.
Let all your kites fly.”
Again, the “glass” referred to here represents a barometer, which measures air pressure. High pressure means fair weather; low pressure indicates rain or storms.
0 likes
-
Rob-TheStormChaser
-
Rob-TheStormChaser
“A coming storm your shooting corns presage,
And aches will throb, your hollow tooth will rage.”
“If your corns all ache and itch,
The weather fair will make a switch.”
Studies have shown that some people experience increased pain when the barometric pressure falls. This is not the case with everyone, but changes in air pressure do seem to cause aches and pains to increase for some folks.
And aches will throb, your hollow tooth will rage.”
“If your corns all ache and itch,
The weather fair will make a switch.”
Studies have shown that some people experience increased pain when the barometric pressure falls. This is not the case with everyone, but changes in air pressure do seem to cause aches and pains to increase for some folks.
0 likes
-
Rob-TheStormChaser
-
Rob-TheStormChaser
-
Rob-TheStormChaser
“Trout jump high
When a rain is nigh.”
Lowering of air pressure sometimes causes trapped gases, created by decaying plant matter on the bottom of a lake or pond, to release. This, in turn, causes microscopic organisms that hide in the plant debris to be dispersed. This, in turn, stimulates small fish to start feeding, which causes larger fish to start feeding on them. A whole “feeding frenzy” may develop, which cause the fish to become active and jump.
When a rain is nigh.”
Lowering of air pressure sometimes causes trapped gases, created by decaying plant matter on the bottom of a lake or pond, to release. This, in turn, causes microscopic organisms that hide in the plant debris to be dispersed. This, in turn, stimulates small fish to start feeding, which causes larger fish to start feeding on them. A whole “feeding frenzy” may develop, which cause the fish to become active and jump.
0 likes
-
Rob-TheStormChaser
-
Rob-TheStormChaser
-
Rob-TheStormChaser
Return to “USA & Caribbean Weather”
Who is online
Users browsing this forum: Cpv17 and 8 guests