MadSci Network: Earth Sciences

Re: How do mountains and canyons effect wind velocity?

Date: Wed Oct 28 16:14:15 1998
Posted By: Suzanne Willis, professor,Northern Illinois University
Area of science: Earth Sciences
ID: 907749618.Es

Hello, Bob -

In general, air (or any fluid) which is forced to narrow its path (by
going through a narrow passage, between mountains, through gorges,
between buildings, or whatever) will flow faster. This is simply a
result of conservation - as long as there isn't extra air being supplied
from anywhere, and none of it is disappearing, then there has to be the
same amount passing any given point on its path per unit time as there
is passing any other point. So if the passage gets narrower, the flow
speeds up (and the pressure decreases). This is called the Venturi effect;
here is a discussion of it (as well as the continuity equation and the
Bernouilli effect) from a course offerred at the University of Michigan:
A general discussion of atmospheric winds, and how they vary with terrain
and in storms of various kinds, can be found in This page also contains
a number of useful, but non-Web, references.

These winds are of particular practical concern to aviators, especially
those flying small unpowered craft such as hang gliders; educational
information for them often contains advice about canyons and other
formations which restrict air passage and therefore can be sources of high

However, the highest winds occur during storms. The highest officially
recorded wind gust in the world is still the 231 mph gust recorded during
a storm on Mt. Washington, New Hampshire in 1934; for a discussion of
this gust, and a refutation of a claim for a higher gust during a 1997
typhoon on Guam, see
In general, Mt. Washington seems to have the worst weather in the US, and
perhaps in the world;  a comprehensive Mt. Washington weather page is at The high probability
of strong winds there seems to be a combination of the general topography
with the height of the mountain.

A wind atlas of the US is available at; this atlas is intended
to show winds as an energy resource and so is relatively large-scale;
however the detailed notes for each map indicate regions where winds may
vary significantly from the average.
A map showing the highest wind gusts possible if showers or thunderstorms
were to occur, and the possibility of both wet and dry microbursts, is
available from the GOES satellite data at These data are updated

It is probable that winds higher than the Mt. Washington gust have occurred
in tornadoes, but they have never been measured directly. Tornado wind
speeds have been estimated by looking at the damage they cause; the most
destructive tornadoes may have wind speeds up to 350 mph. Here are some
links about tornadoes:

 In summary, I would say: the most dangerous place in the US for winds is
Mt. Washington. No winds as high as 400 mph have been recorded or even
suggested. The highest winds come from tornadoes, which can arise
relatively quickly but not really "from nowhere". Thunderstorms can also
result in high and unpredictable winds. Clear-sky wind gusts also occur,
but do not get as strong as storm gusts; they can still be dangerous,

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