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How do storms in the middle and high latitudes
form? |
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How do upper level winds influence storm
formation? |
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What are the wind flow patterns in a developing
storm system? |
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A wave cyclone begins along the polar front,
where cold polar air meets warm subtropical air. |
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The (stationary) front is locally a trough of
low pressure. |
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Air flows parallel to the front, but in opposite
directions. |
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Because of the different wind directions, a
frontal wave can form. |
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The region of lowest pressure is at the junction
between the two fronts. |
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Green shaded region is where rain is. |
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Next an open wave forms with lower pressure at
the center. |
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Precipitation forms in a wide band in front of
the warm front and a narrow band near the cold front. |
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Energy comes from warm air rising, latent heat,
and wind flowing toward low. |
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The faster moving cold front moves closer to the
warm front, reducing shrinking the warm sector. |
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Eventually, the front becomes occluded. At this point the storm is most intense. |
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The point where the cold, warm, and occluded
fronts meet is called the triple point. |
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A new wave may start at this secondary low. |
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The center gradually dissipates as cold air lies
on both sides of the original front. |
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Without the supply of energy from warm air
rising and precipitation, the original front gradually disappears, leaving
a low and a stationary front. |
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Low 1 is just forming, Low 2 is an open wave,
and Low 3 is dissipating. The
average speed of a cyclone is 25 knots. |
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Strengthening of a cyclone is called
cyclogenesis. |
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Regions in US where this frequently occurs: east
slope of Rockies, the Great Basin, Gulf of Mexico, and Atlantic Ocean east
of Carolinas. |
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Air flow converges towards a low, acting to
increase the pressure. |
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Air flow diverges away from a high, acting to
decrease the air pressure. |
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How does a low intensify? |
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Where the isobars (and wind flow) get closer
together the air is converging, while when the isobars get further apart
the air is diverging. |
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A surface high will intensify if there is
converging air above it. |
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A surface low will intensify if there is
diverging air below it. |
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Note offset between surface and above highs and
lows. |
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Upper level wind influences the formation of
surface highs and lows. |
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Large storm systems at middle and high latitudes
form along the polar front. |
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According to the polar front theory, storms
start as a frontal wave, develop into an open wave, and eventually
dissipate. |
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Whether a storm intensifies is determined in
part by upper level convergence and divergence. |
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