How do storms develop over large land masses? Is it that there's massive amounts of moisture in the air?

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answers:
Red say: 9
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TQ say: Here's how storms develop over large land masses.

Short answer:
It's not b/c there's massive amounts of moisture in the air.
And it's also not b/c of any of the world-class hand-waving on display in the other answers.

Longer answer:
Cyclogenesis is the name meteorologist give to a developing storm.
Three main ingredients are need for cyclogenesis to occur:
- Temperature contrast
- Lifting mechanism
- Moisture

Storms begin to form in the mid-to-upper levels of the troposphere where the air flows in undulating waves ... then work their way down to the surface.

- The RED (BLUE) stripe in the upper panel is a region of ASCENDING (DESCENDING) air.
- Beneath RED (BLUE) stripe at the surface is an area where air is being pulled toward (away from) a central point which creates LOW (HIGH) pressure.

- As the air is drawn toward a central point ... the rotation of the earth causes the wind to turn to the right and rotate counter-clockwise in the Northern hemisphere. Moisture in the rising air around the LOW cools ... condenses into clouds ... and creates precipitation.

The general storm movement is easterly pushed along by westerly winds in the mid- and upper levels.
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busterwasmycat say: Large scale systems are frontal systems, where there is a conflict between two air masses (high pressure zones where air is descending from the upper atmosphere and spilling out laterally). Typically, one air mass is a lot cooler and dryer than the other, so the moisture is brought in one air mass and the condensation is caused by the other air mass.

Low pressure happens because that air in the upper atmosphere that is descending out in the high pressure zone must get replaced somehow, right? The frontal zones are where the air return happens. Air rises and moisture plops out.

What you have, in essence, is two different circulation cells, and storms happen where the two cells come into contact. There is often a lot of energy exchange involved. Think of it as a very fast equivalent of a continent to continent collision in plate tectonics that causes mountains to rise: two masses pushing at each other and the only way out is up.
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CarolOklaNola say: Partly but it is more low pressure systems and Hugh pressure systems. There is normally a 3 to 5 day cycle in temperatures. . Some high pressure sys teams do not make it all the way to the GLF, and pressure systems can stall and dump a lot of rain like Harvey did. There are lake effect snow. There are .micro climates. It can pour in one part of New Orleans or Greater Oklahoma City and barely drop of rain or flake of snow or sleet falls some where else. I literally saw snow in one side if straight line and none in the other side one year. It may have been 9 or 13 years ago.
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Sammy say: I think it's due to 2or more pressure systems colliding together.
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