Why does the Western US get less rain than the Eastern US?

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  • Jim
    Lv 7
    1 month ago

    Cold air warming vs warm air cooling

    • TQ
      Lv 7
      1 month agoReport

      👀 👀 👀 meteorology

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  • TQ
    Lv 7
    1 month ago

    The reasons why the Western [sic] US [sic] get less rain than the Eastern [sic] US [sic] are related directly to 1) the semi-permanent areas of HIGH pressure located offshore of both east and west coasts and 2) the jet stream responsible for their creation.

    On the west coast of the U.S. .. the clockwise circulation are the HIGH transports cool dry moist air polar/arctic air into the mid-latitudes. The southerly motion toward lower latitudes decreases deep vertical layer rotation (vorticity through the conservation of angular momentum) producing downward vertical motion.

    Downward vertical motions leads to evaporation ... dissipation of clouds ... and no precipitation.

    The exact opposite mechanics are observed on the east coast of the U.S.

    On the east coast .. the clockwise circulation are the HIGH transports warm moist tropical air into the mid-latitudes. The northerly motion away from lower latitudes increases deep vertical layer rotation (vorticity through the conservation of angular momentum) producing upward vertical motion.

    Upward vertical motions leads to condensation ... clouds ... and precipitation.

    The final reason is related to the Westerlies (sometimes referred to incorrectly as the jet stream). The Westerlies accelerate as they move off land and out over open water which favors the development of a long wave trough of LOW pressure where upward vertical motions are also present.

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  • 1 month ago

    More and younger mountain ranges in the West. Moist air comes in from the west and flows up over the mountains, cooling as it rises. Cold air holds less moisture than warm air, so rain falls on the windward side. Once over the peaks, the air falls and warms up. But dry air heats up more than wet air does so the western states east of the Rockies give up their moisture to the air. By the time the air reaches the East, it has become moist again. While the same thing happens to some extent over the Appalachians, these are older mountains and worn down, so the effect is less. The dividing line between the dry West and the moist East pretty much follows the hundredth meridian.

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    • οικος
      Lv 7
      1 month agoReport

      I never said that it didn't.. And you are stretching the meaning of
      "localized" when referring to the rain shadow of the Rockies.

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  • 1 month ago

    The Western U.S. is basically a desert.

    The Rocky Mountain Range, along with the Pacific Ocean's southern warmer waters and the northern colder waters creates a semi-permanent high pressure system the sits over this region most of the time. If you understand precipitation, you know that higher pressures and temperatures allow the air to hold greater amounts of water before precipitation can occur. In order for rain to fall, the barometric pressure, or water saturation point, has to drop enough for the air to condense enough to create rain drops that gravity can pull to the ground.

    Usually what happens is as the tilt of the earth begins to apex towards winter in the northern hemisphere, temperatures increase in the southern hemisphere which cause the low pressures of the arctic to descend south. Which pushes the high pressure over the western U.S. to the southwest, bringing lower temperatures and pressures over the region. Causing it to rain in the area.

    The great oceanic currents also play a role in this, but as you start to take more and more variables into play, the explanation becomes increasingly complex to explain. However, that's the basics of why it rains more east of the Rockies.

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    • TQ
      Lv 7
      1 month agoReport

      "higher pressures and temperatures allow the air to hold greater amounts of water ..." your words ... not mine

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  • Dze
    Lv 7
    1 month ago

    no expert .. but i assume most of the moisture thats 'put into' the atmosphere comes from ocean ... you got the rockies pretty much between the ocean and a large area of the west .. theres alot more water around the southern and eastern US for storms to feed on and build up, especially in warmer times of the year ...

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