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32 Cards in this Set
- Front
- Back
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What are the basic requirements for thunderstorm formation?
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Moisture, unstable air, lifting action
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How do thunderstorms initiate?
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Lifting to point of free convection which triggers cumulus cloud through the life cycle
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What are the three stages of thunderstorm cells?
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Cumulus, mature, dissipating
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What is the cumulus stage of a thunderstorm?
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First Stage: updraft (surface to 000s of feet above top), no precipitation, significant turbulence, low hazards
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What is the mature stage of a thunderstorm?
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Second Stage: rain / ice fall, updraft continues, downdraft begins, hazards, average height = 25,000 feet
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What is the dissipating stage of a thunderstorm?
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Third Stage: dominated by downdrafts with precipitation, anvil form develops, hazards remain
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What are the 6 hazards that accompany thunderstorms (and worst two)?
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Extreme turbulence, hail (worst two), microbursts, severe icing, lightning, tornadoes
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What is the range of turbulence in thunderstorms?
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ground to 5,000' above cloud tops, gust fronts 5-20 miles from thunderstorm
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What is a roll cloud?
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Lower leading edge of a cumulonimbus cloud - marks strong eddy currents, identifies wind shear & turbulence
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What is the pressure variation associated with thunderstorms?
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1. Rapid fall in approach; 2. Abrupt rise at first gust / rain showers; 3. Gradual return to normal
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What is the vicinity and size of hail around a thunderstorm?
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45,000' high, 30 miles downwind from the core, 1/2 to 3/4 inch
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Where are lightning strikes most likely in a thunderstorm?
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Within 8 degrees or 5,000' of freezing level, precipitation, clouds or turbulence
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What are lightning hazards?
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Blindness, compass error, electronics damage, ignition of fuel, skin perforations
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What is a tornado?
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Violent, intense, rotating column of air that descends from cumulonimbus clouds in funnel/tube shapes
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What are the two similar phenomina to tornados?
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Funnel clouds (no touchdown), waterspout (touchdown in water)
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What is the size and speed of a tornado vortex?
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Several hundred to 2.5 miles wide, 300 mph, 30-40 kts GS
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What are indications of invisible tornado vorticies?
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Swirls in cloud base, dust whirls boiling along the ground
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What is a microburst?
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Intense, highly localized downwarde atmospheric flow with velocities of 2,000 - 6,000 fpm
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What are the velocities associated with a microburst?
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2,000 - 6,000 fpm, 20-200 kts differential, 1/4 to 2.5 miles in diameter
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What is the source of microbursts?
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Any convective cloud (not just cumulonimbus)
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What is the life span of microbursts?
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5-10 minutes
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What does ground-based doppler radar detect?
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Microbursts, tornadoes, low-level wind shear activity
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What are reports that may indicate microbust activity?
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Gusty winds, heavy rain, severe thunderstorms, PIREPS, wind shear warning system
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What are visual cues of microburst activity?
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Virga, localized blowing dust, rain shafts diverging, roll clouds, vivid lightning, tornado activity
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Where does icing generally occur in thunderstorms?
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Where the free-air temperature is at or below freezing (generally NOT in the bottom 1/3 of the cell)
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What are the three useful radar information pieces?
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Tops (above 35,000 = extreme turbulence & hail), Scattered echos (can be circumnavigated), separation echoes < 30 mies (clear air turbulence and hail between thunderstorms)
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What are the priority recommendations in avoiding thunderstorms?
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1. Fly around. 2. Fly over the top. 3. Fly under. 4. Fly through lower 1/3 of storm.
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What is the guidelines for flying around a thunderstorm?
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5-10 miles in diameter, so it is possible
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What is the guidelines for flying above a thunderstorm?
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Maintain separation of 1,000' for every ten knots of wind speed at altitude of tops
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What is the guidelines for flying underneath a thunderstorm?
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Select an altitude 1/3 the distance from the surface to the base of the cloud (downburst / microburst danger)
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What is the guidelines for penetrating a thunderstorm?
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Penetrate through the lower 1/3 of the storm (4,000 - 6,000 unknown), at right angles, don't turn around, maintain level flight attitude (using gyro, reliable) and accept variations in altitude, airspeed and rate of climb (all unreliable)
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What are the procedures for penetrating a thunderstorm?
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Secure, Pitot heat, engine anti-ice, below freezing level or above -20 degrees C, turbulent air penetration speed, disengage autopilot, don't chase airspeed, minimize power changes, don't turn back
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