Aviation Weather: Weather Hazards

1. AF 202 – Chris Dimoulis Aviation Weather: Weather Hazards

2. Objectives Thunderstorms Wind Shear Turbulence Icing Fog Additional Hazards

3. Thunderstorms

4. Thunderstorms Requirements for thunderstorms Moist air Instability Initial lifting action

5. Thunderstorms If you have the moisture and instability, you need a lifting action to “set off” the instability Heating (thermals) Orographic lifting Fronts Low-level Convergence Upper-level Divergence

6. Thunderstorms Heating (Thermals) When the ground becomes much warmer than the air above it, the Lapse Rate is GREATER than standard (2-3 deg /1000 ft) The slightest displacement of that warm air (say a wind gust) will send that warm air into a vertical motion This creates “bubbles” of rising warm air that we call thermals

7. Thunderstorms Heating (Thermals) cont’. Thermals can have horizontal dimensions of a few hundred to a few thousand feet. Vertical speeds can be a few hundred F.P.M. to 2,000 F.P.M Thermals can happen as long as the ground is warmer than the air above it (i.e. cold front passage) Most common in hottest months and time of day (i.e. Southern Illinois in the summer)

8. Thunderstorms Orographic lifting A fancy name for when air is lifted due to a mountain or other terrain Fronts The ‘wedge’ of the warm or cold front lifts the warm air mass and ‘sets off’ any instability

9. Thunderstorms Low-Level Convergence Convergence is when the air horizontally converges into an area This creates a higher pressure and the only place for that air to go is up Upper-Level Divergence Divergence is when the air horizontally diverges from an area This creates a upper area low pulling air up from the surface

10. Thunderstorms Three stage of the thunderstorm Cumulus Mature Dissipating

11. Thunderstorms

12. Thunderstorms Cumulus Stage Updrafts predominate and are continuous Updraft area is much larger than just one individual thermal You can visually see one particular cloud growing faster than all others (and all others may even shrink as the feed the one) This stage could grow the cloud all the way to a towering cumulus (about 20,000 feet) Usually does not produce precipitation, but can (though it will not become mature)

13. Thunderstorms Mature Stage Begins when precipitation-induced downdrafts reach the ground Lightning and thunder Well organized circulation in the cloud Top of cloud reaches into the lower stratosphere The well known anvil shape is formed A cumulus stage that produces precipitation does not reach mature stage and does not produce lightning and thunder

14. Thunderstorms Dissipating Stage Characterized by precipitation and downdrafts Updrafts are cut off so there is no more development Ends with stratiform clouds since the anvil layer is often an ice cloud, it still lingers after the storm dissipates

15. Thunderstorms Single Cell Cumulus stage lasts 15 minutes Mature stage lasts about 30 minutes Total lifespan of a single cell storms is about 1 hour

16. Thunderstorms Multicell Thunderstorms

17. Thunderstorms Multicell Thunderstorms The key to prolonged life is the gust front Cumulus stage clouds develop As they move into mature or dissipating stage, more cumulus stage clouds develop

18. Thunderstorms Multicell Thunderstorms

19. Thunderstorms Supercell Thunderstorms

20. Thunderstorms Supercell Thunderstorms Produces the extreme convective activity Strong updrafts producing cloud bulges above the anvil top Updrafts and downdrafts remain separated which prolongs its life

21. Thunderstorms

22. Thunderstorms

23. Thunderstorms

24. Thunderstorms

25. Thunderstorms

26. Hazards Tornados A violently rotating column of air Winds up to 200 miles per hour (or more!) Incredible localize damage

27. Hazards

28. Hazards

29. Hazards

30. Hazards Hail A result of very strong updrafts Can be thrown out the top of the thunderstorm Tenths of an inch to larger than a softball

31. Lightning Electric discharge Heats surrounding air to 50,000 deg. F. causing air to rapidly expand That’s what causes the shockwave called thunder In Cloud, Cloud to cloud, cloud to ground

32. Hazards

33. Hazards Downdrafts Can cause low level wind shear

34. Pilot advice Stay 20 NM away from a thunderstorm And don’t fly through or under one!

35. Wind Shear and Turbulence

36. Wind Shear Definition: A change in wind direction and/or speed within a very short distance Causes of Wind Shear Microburst Passing fronts Temperature Inversions

37. Wind Shear Low Level wind shear is most hazardous to pilots A sudden increase in wind or a switch from tail wind to head wind could give the pilot false indications

38. Turbulence Technically defined as “bumpiness in flight” Types Low Level Turbulence (below 15,000ft) In and near thunderstorms Clear air Mountain wave

39. Low Level Turbulence Mechanical Turbulence The stronger the wind, the higher mechanical turbulence can reach

40. Low Level Turbulence Thermal Turbulence An unstable cold airmass over warm ground is prime ingredients for thermals Hot air rising causes vertical motion

41. Clear Air Turbulence Occurs in the free air away from any convective activity Above 15,000 ft where beyond the affects of low level turbulence Cannot usually be seen unless there are any clouds to show affect

42. Clear Air Turbulence

43. Clear Air Turbulence

44. Mountain Wave Turbulence Stable air flowing over mountains Can affect air patter for 100s of miles

45. Mountain Wave Turbulence

46. Icing

47. Icing Icing occurs… When there is visible moisture or precipitation Temperatures of aircraft skin are below freezing

48. Icing Types Clear Rime Mixed

49. Icing If you pick up icing 180 to get out of cloud Climb to find temperature inversion or sun Descend to warmer temps

50. Fog