WIND DANGERS
compiled by Dee Finney
FROM: http://k12.ocs.ou.edu/teachers/reference/atmosforce.html
Wind speed and direction respond to pressure gradient forces that exist between high and low pressure areas. In the Northern Hemisphere and because of the rotation of the earth, winds circulate in a clockwise fashion around areas of high pressure and in a counter-clockwise manner around regions of lower pressure. Air pressure decreases relatively slowly with height in regions dominated by warm air and relatively rapidly with height in areas where cold air prevails. As a result, wind patterns in the upper atmosphere tend to flow in an oscillating manner around major pockets of warm and cold air.
Wind results from physical forces that act on the air.
A force is an influence on a body which causes the body to accelerate (change speed or direction). Newton's First Law of Motion states that a body at rest will remain at rest, and a body in motion will remain in motion unless acted upon by an unbalanced force. If forces balance (no net force), then we have either no motion or uniform motion in a straight line.
Newton's 2nd Law of Motion states that the acceleration (rate of change of velocity) of a body is directly proportional to the net force upon the body, or F = ma, where F = force, m = mass, and a = acceleration.
Gravitational force- keeps the molecules in the atmosphere from moving into space. Gravity's influence is stronger
near the earth's surface and weaker aloft.
Vertical pressure gradient force- closely balances gravity so that all the molecules in the atmosphere are not
forced into the lowest meter above the ground. The vertical pressure gradient force results from molecules in the
high pressure near the earth's surface trying to move upward where the pressure is lower.
Coriolis force- the force that results from Earth's rotation. The Coriolis force solely results
from living on a rotating object -- Earth. It acts only on objects moving with respect to the earth's surface (e.g.,
the air, planes, birds, missiles, etc.). It is only significant over long distances (e.g., hundreds or thousands
of miles) and long time spans (e.g., 12 hours or longer). Hence, tornadoes are not influenced by the Coriolis force.
Neither is the water draining in your sink. The Coriolis force always will deflect objects to the right
in the Northern Hemisphere and to the left in the Southern Hemisphere. The Coriolis force will never change the
speed of an object, only its direction
Friction- the drag exerted on the air by the earth's surface (e.g., plants, trees, buildings, mountains, etc.).
Centrifugal force- the tendency for a body to resist a change in direction
If Earth did not rotate, air currents would flow directly from areas of high pressure to areas of low pressure. However, because Earth does rotate, air currents ultimately become involved in a tug-of-war between pressure gradient forces and the Coriolis force. The result is that air circulates counterclockwise around areas of low pressure in the Northern Hemisphere and clockwise around areas of high pressure
DANGER OF WIND IN MOBILE HOMES
HURRICANES AND SPINOFF TORNADOS
AVOID TRAVEL IN THESE CONDITIONS
Blowing/shifting snow: Loose snow and wind force more than 11 m/sec (fresh breeze, 18 knots) with blowing snow partially obstructing road view and/or danger of road conditions deteriorating within the next few hours.
Blizzard: Wind force 16 m/sec (moderate gale, 30 knots) or more and snowfall, difficult traveling weather, considerable danger of road conditions worsening at short notice.
Fog: Heavy fog with obstructed vision. In the interest of traffic safety motorists are advised to proceed with caution.
ALASKA - WINTER STORM WARNINGS
PACIFIC OCEAN WEATHER AND WINDS
PROTECTING YOURSELF FROM COLD AND WIND