1. MOUNTAIN FLYING Dr. Chip West National Weather Service

2. TERRAIN

3. WEATHER-RELATED ACCIDENTS 050100150200250300 NTSB Accident Data for 1995 Obscurations Thunderstorms Icing High Density Altitude Turbulence Low Ceilings Reduced Visibilities Adverse Winds Fatal AccidentsNon-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. Observations Types –ASOS –AWOS ASOS –“tunnel view –“Clr” < 12,000ft. –Cloud heights AGL –Point visibility

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

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. DOWNSLOPE FLOW WIND WINDWARD LEEWARD 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 Wind or Updraft Wind Sun’s heating

23. Valley Wind Diurnal heating induces up valley wind

24. Mountain Breeze Evening cooling induces down valley or drainage winds

25. WARM COLD FRONTS WIND SHEAR TURBULENCE

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