MART Vol. II MO/MP - NESA - Civil Air Patrol

the mountainside. The stronger the wind gets, the greater the downward pressureand turbulence. Consequently, in approaching a hill or mountain from the leewardside, a pilot should gain enough altitude well in advance. Because of thesedowndrafts, it is recommended that mountain ridges and peaks be cleared by atleast 2,000 ft. If there is any doubt about having adequate clearance, the pilotshould turn away at once and gain more altitude. Between hills or mountains,where there is a canyon or narrow valley, the wind will generally veer from itsnormal course and flow through the passage with increased velocity andturbulence. A pilot flying over such terrain needs to be alert for wind shifts andparticularly cautious if making a landing.3.1.5 Winds around pressure systemsCertain wind patterns can be associated with areas of high and low pressure.Air flows from an area of high pressure to an area of low pressure. In theNorthern Hemisphere during this flow the air is deflected to the right because ofthe rotation of the earth. Therefore, as the air leaves the high-pressure area, it isdeflected to produce a clockwise circulation.HAs the air flows toward the low-pressure area, it is deflected to produce acounterclockwise flow around the low-pressure area.LAnother important aspect is air moving out of a high-pressure area depletesthe quantity of air. Therefore, highs are areas of descending air. Descending airfavors dissipation of cloudiness; hence the association that high pressure usuallyportends good weather.By similar reasoning, when air converges into a low-pressure area, it cannotgo outward against the pressure gradient, nor can it go downward into the ground;45