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been caused by these events. The wet microburst is found in the middle of an active thunderstorm or intense rain shower and avoiding the strong downdraft is relatively easy. The dry microburst, however, is somewhat more insidious because it occurs with little or no warning in the clear air beneath virga. Dry microbllrsts are common in and near the Rockies and other moun› tainous areas of the western U.S. in the summer. The formation of the dry micro burst is likely when thunderstorms with bases above about 3,000 to 5,000 feet AGL exist and the temperature/ dew point spread on the surface is more than about 40 degrees. If dust is blowing underneath one of these high based thunderstorms, stay clear until the event passes (usually only a few minutes). 

## Temperature Inversions 

Mountain valleys are often conducive to the formation of tempera› ture inversions and valley fog at night. This should play a part in your arrival and departure planning. Since the inversion breaks and the fog dissipates by late morning, you may have to delay slightly at some airports. 

## Density Altitude Effects on the Airplane 

There are numerous ways that density altitude affects the air› plane. For example, a normally aspirated engine will lose 3% of its power per thousand feet of density altitude increase. Next, as density altitude increases, the wings have less dense air with which to create lift. Since a pro› peller is an airfoil, it, too, will be less efficient. 

## Effects on Performance 

All of these factors affect the overall performance of the airplane. At higher density altitudes, takeoff and landing distances are increased, rate of climb and actual service ceiling are decreased, true airspeed is higher for a given indicated airspeetl, and turning radius is larger at high altitude at a given indicated airspeed. 

To help regain some of the lost takeoff and landing performance at high density altitudes. you should reduce the weight at \rvhich you 

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