40 Minutes

1. References: -FTGU, pages 132, 144, 145, 148 to 154 -Air Command Weather Manual, Chapters 9 and 15 Meteorology 5.10 Extreme Weather 40 Minutes

2. 5.10 Meteorology - Review What type of weather is associated with a: a. cold front cumulus clouds, high ceiling, turbulence, showers, good visibility b. warm front stratus cloud, low ceiling, smooth air, steady precipitation, restricted visibility What is an occluded front? When a cold front catches up to a warm front and the air mixes. Creates variable weather and a TROWAL. What clouds tell that a warm front is approaching? Cirrus, Cirrostratus, Altostratus, Nimbostratus, Stratus

3. 5.10 Meteorology – Severe weather • MTPs: • Thunderstorms • Requirements for Thunderstorms • Stages of a Thunderstorm • Thunderstorm Weather • Hazards of a Thunderstorm • Aircraft Icing • Hazards of Squalls and Tornadoes

4. 5.10 Meteorology – Thunderstorms • The basic requirements for a thunderstorm to develop are: • Unstable air • A Lifting Force (generally convection) • High Moisture Content • When are they likely to occur? • With the passage of a cold front • From daytime heating – hot summer days • Interesting Factoid: At any one time there are 1800 TS occurring world wide

5. 5.10 Meteorology – Thunderstorms Stages of a Thunderstorm Cumulus stage Mature stage Dissipating Stage

6. 5.10 Meteorology – Thunderstorms • Cumulus Stage: • Strong updrafts prevail throughout the cell • Usually no precipitation (yet…) • Temperatures in the cloud are higher than surrounding air.

7. 5.10 Meteorology – Thunderstorms • Mature Stage: • Updrafts of up to 6,000 feet per minute • Downdrafts start in the middle, up to 2,500 ft/min • Precipitation starts as water drops are too heavy for surrounding air to suspend any further • Falling raindrops cause very large, fast downdrafts • Downdrafts of up to 6,000 ft/min at this point • Usually 15-20 minutes in duration, though may be as long as an hour.

8. 5.10 Meteorology – Thunderstorms • Dissipating Stage: • Entire cell becomes an area of downdraft • Precipitation Stops • Cell loses its energy • Indicated with the top of the cloud forming an anvil shape.

9. 5.10 Meteorology – Thunderstorms

10. 5.10 Meteorology – Thunderstorms They have very complex weather patterns; wind shear can be found on all sides of the storm • As the thunderstorm matures, strong downdrafts develop and the cold air rushing down spreads out along the ground well in advance, undercutting the warm air - gust front.

11. 5.10 Meteorology – Thunderstorms • Macroburst: A severe and damaging downward rush of air with a diameter of 2 nautical miles or more is called a These can last up to 20 minutes • Microbursts: A downward rush of air with a diameter less than 2 nautical miles and peak winds that last less than 5 minutes • Downdrafts can have vertical speeds as great as 6,000ft/min, with horizontal wind speeds as high as 80 knots

12. 5.10 Meteorology – Thunderstorm Hazards • Lightning • A discharge of electrical energy produced by a thunderstorm • A positive charge collects on the top of the cloud while a negative charge exists on the bottom • Thunder • Created by the rapid increase of temperature (and therefore pressure) of the air around the lightning bolt • Hail – can be crippling to a flying operation • Icing – can occur at any level within the cloud (even when not in cloud!). • Rain – can be very heavy at times • Pressure variance – Altimeter reading errors

13. 5.10 Meteorology – Thunderstorm Hazards AIRPLANE

14. 5.10 Meteorology – Thunderstorm Hazards • DON’T fly through a thunderstorm!!!!! • Avoid landings and takeoffs near them • Don’t fly under them • Reduce speed at first indication of turbulence • If you fly around one, stay at least 10-15 miles away, and fly around the right side

15. 5.10 Meteorology – Aircraft Icing Aircraft Icing • Icing increases aircraft weight, drag, stall speed, and decreases lift • Do not fly when there is any contamination to the critical surfaces of an aircraft • Wings, Vertical/Horizontal Stabilizers, Control sufaces, Propeller

16. 5.10 Meteorology – Aircraft Icing Types of Icing 1. Frozen Dew • A white semi-crystalline frost that covers the surface of the aircraft • Frozen dew happens on cold clear winter nights • Water vapour hits the surface of the aircraft and sublimation occurs

17. 5.10 Meteorology – Aircraft Icing 2. Hoar Frost • a white, feathery, crystalline formation that covers the entire surface of the aircraft • Very similar to frozen dew • The only difference is that hoar frost can happen during flight.

18. 5.10 Meteorology – Aircraft Icing • 3. Rime Ice • An opaque, or milky white ice that accumulates on the leading edge of the wing, and on antennas • It is formed by the almost instantaneous freezing of small supercooled water droplets • This fast freezing causes air pockets to be trapped in the ice, giving the opaque quality.

19. 5.10 Meteorology – Aircraft Icing 4. Clear Ice • A heavy coating of glass like ice which forms over the entire surface (or a good portion of it) of a wing • It is formed as large supercooled water droplets freeze slowly as they move rearward to cover the wing • Most often occurs with temperatures between 0 - 10 °C

20. 5.10 Meteorology – Squall Line • Squall Line • Long line of squalls and thunderstorms which sometimes accompanies the passage of a cold front • Usually associated with a fast moving cold front undercutting an unstable warm air mass • May form anywhere from 50 to 300 nautical miles in advance of the front.

21. 5.10 Meteorology – Tornadoes Tornadoes • Violent, circular whirlpools of air associated with severe thunderstorms • Very deep, concentrated low pressure areas • Shaped like a funnel hanging out of the cumulonimbus cloud • Dark in appearance due to dust and debris sucked in • Diameter ranges from 100 feet to half a mile • Move at speeds of 25 to 50 knots • Wind speeds as great as 300 knots.

22. 1. What 3 things are needed for thunderstorm to develop? ______________________________ ______________________________ ______________________________ 2. What are the 3 stages to a thunderstorm? 5.10 Meteorology – Confirmation

23. 5.10 Meteorology – Confirmation 3. Name the following ice types 4. Where are squall lines found?