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## High and Low Pressure Patterns 

As you analyze the mountain weather before your flight, pay spe› cial attention to the position of the highs and lows to give clues to the wind speed potential. For example, in the winter, a high often sets up over the Four Corners area in southwest Colorado. This is often coupled with a low pressure centered in eastern Colorado or western Kansas. The result can be very strong westerly winds and• dangerous turbulence in the high terrain for days at a time. 

## Mountain Wave 

When the wind speed is above about 25 knots and flowing perpen› dicular to the ridge lines, the air flow can form waves, much like water flowing over rocks in a stream bed. The waves form down wind from the ridge line and will 

be composed of very strong up and down drafts, plus dangerous rotor action under the crests of the waves. If enough moisture is present, lenticular clouds can form to give a visual indication of the wave action. These clouds are reported in the remarks section of hourly sequence reports as ACSL (altocumulus standing lenticular) or CCSL (cirrocumulus standing lenticular). 

## Winds Through Passes 

Just as the flow through a carburetor speeds up in the restriction of the throat, wind flowing through the narrow restriction of a moun› tain pass will also speed up. When the winds are forecasted above about 20 knots, be aware that the speed in passes may cause turbu› lence and drafts that should be avoided. 

## Orographic Lifting 

As the wind blows moist air upslope, it will cool and may form clouds. If, as is often the case winter, the air is stable, the clouds will stay close to the mountain, forming a "cap" cloud. However, if the air is unstable, as is usually the case in the summer, this initial lifting will be enough to start convection and result in thunder› storms forming. 

## Microbursts 

Microbursts have received much space in the aviation and popular press in the pasl several years because of their implication in many serious airline accidents. Many light aircraft accidents have also 

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