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MOUNTAIN FLYING

MOUNTAIN FLYING. Dr. Chip West National Weather Service. TERRAIN. WEATHER-RELATED ACCIDENTS. Adverse Winds. Reduced Visibilities. Low Ceilings. Turbulence. High Density Altitude. Icing. Thunderstorms. Obscurations. 0. 50. 100. 150. 200. 250. 300. NTSB Accident Data for 1995.

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MOUNTAIN FLYING

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  1. MOUNTAIN FLYING Dr. Chip West National Weather Service

  2. TERRAIN

  3. WEATHER-RELATED ACCIDENTS Adverse Winds Reduced Visibilities Low Ceilings Turbulence High Density Altitude Icing Thunderstorms Obscurations 0 50 100 150 200 250 300 NTSB Accident Data for 1995 Fatal Accidents Non-Fatal Accidents

  4. Valley Fog and Stratus • Diurnal Cycle • Outside vs Valley Observations • Season – Fall to Spring

  5. Fog and Stratus

  6. Preflight .Observations – sources .ASOS/AWOS limitations .Valley fog/stratus .Winds aloft .Terrain effects on wind .Frost

  7. Types ASOS AWOS ASOS “tunnel view “Clr” < 12,000ft. Cloud heights AGL Point visibility Observations

  8. Weather Takeoff Factors • Altitude • Temperature • Humidity • Wind direction • Worse case combination?

  9. Enroute –To Where? • Always leave yourself the option of turning to lower terrain or back • Forecast/observed cloud heights vs wind direction and weather patterns • Terrain/wind induced turbulence • Mountain wave • Venturi effect • Valley winds • Icing • Approaching/crossing ridges • How to fly valleys

  10. Terrain effects on wind • Up to a doubling of reported speeds when flow channeled between peaks • Up to a doubling of reported speed when forced over or around a peak, ex. Grandfather mountain. • Diurnal effects • Morning and evening winds

  11. Terrain Effects on Wind Doubling or more of speed around peaks or between peaks

  12. Turbulence over Ridges • < 20 kts = Light to Moderate • 20 – 30 kts = Moderate to occasional Severe • > 30 kts = Moderate or frequent Severe

  13. Mountain Waves

  14. MECHANICAL TURBULENCEMOUNTAIN WAVE 70 60 50 40 30 20 10 0 FAVORABLE CONDITIONS -WINDS 25 KTS OR GREATER ACROSS -WINDS INCREASING WITH HEIGHT -STABLE ATMOSPHERE WAVE LENGTH 5 TO 30 MILES STRATOSPHERE TROPOPAUSE TROPOSPHERE 1000’s OF FEET LENTICULAR CLOUD WIND ROTOR CAP CLOUD TURBULENCE

  15. MOUNTAIN WAVE CLOUDS CCSL ACSL ROTOR

  16. RESPONSE ITEM THE EFFECTS OF MOUNTAIN WAVES OFTEN EXTEND FROM THE SURFACE TO A. LESS THAN 5,000 FEET. B. THE ALTITUDE OF THE MOUNTAIN CREST. C. SLIGHTLY ABOVE THE TROPOPAUSE. A. LESS THAN 5,000 FEET. B. THE ALTITUDE OF THE MOUNTAIN CREST. C. SLIGHTLY ABOVE THE TROPOPAUSE.

  17. Crossing Ridges

  18. How to fly valleys

  19. WIND DOWNSLOPE FLOW LEEWARD WINDWARD FAVORABLE CONDITIONS • WINDS MODERATE OR GREATER ACROSS MOUNTAINS

  20. RESPONSE ITEM IN ORDER TO AVOID AN ACCIDENT BY RAPIDLY DESCENDING INTO THE MOUNTAIN THE PILOT SHOULD: A. CLIMB 5,000 FEET OR MORE ABOVE CREST. B. DECREASE SPEED AT CREST HEIGHT. C. FLY AT CREST HEIGHT BUT STAY OUT OF DOWNDRAFT. A. CLIMB 5,000 FEET OR MORE ABOVE CREST. B. DECREASE SPEED AT CREST HEIGHT. C. FLY AT CREST HEIGHT BUT STAY OUT OF DOWNDRAFT.

  21. Mountain Winds

  22. Anabatic Windor Updraft WindSun’s heating

  23. Valley WindDiurnal heating induces up valley wind

  24. Mountain BreezeEvening cooling induces down valley or drainage winds

  25. FRONTSWIND SHEAR TURBULENCE WARM COLD

  26. FRONTS MECHANICAL TURBULENCE STRONG GUSTY SURFACE WINDS

  27. Arrival/Landing • “Localized” weather • Wind, effects of local terrain on • Time of day • Surrounding terrain

  28. Safety Summary • Always remain in a position so you can turn toward lowering terrain – 45 & down • Never fly beyond the point of no return – 180, idle

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