What Causes Cold Air Drainage Into The Platte River Valley?
By definition dry cold air is denser than warm moist air. Due to the
effects of gravity and terrain, this cold air "drains" down the Sandhills
and into the Platte River Valley. This phenomena is one reason why
those living in the Platte River Valley experience seasonally colder
temperatures at night - as a direct result of topography!
Definitions from the American Meteorologic Society
Glossary of Meteorology
Drainage Wind— Cold air runoff winds that are produced
when air in contact with terrain surfaces is cooled and flows
downslope and/or downvalley.
This generic term is often used to indicate aggregate downslope
(katabatic) and downvalley flows, when it is difficult to distinguish
between the two. This happens frequently in basins, at the upper
end of valleys, in complicated topography where the downslope
and downvalley directions are not perpendicular, and in simple
valleys when the weaker and shallower downslope flows are
masked or overwhelmed by the stronger downvalley flow.
Over even gently sloping topography, drainage winds also refer
to gravity winds that drain cold air into frost hollows, river valleys,
and other lower-lying terrain. See downslope wind.
(The topographic image above shows higher terrain in blue shades with
lower terrain in pink - please note how well the Platte River Valley appears)
(Note: In the 2 topographic images above, you can clearly see the higher
terrain of the Nebraska Sandhills to the northwest and north of North Platte.
Click images above for larger sized resolution
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