CBM CBM Severe Weather and Hazardous Conditions 2 — Questions and Answers
Question 1: What is 'explosive cyclogenesis' (commonly called a 'bomb cyclone')?
- A tropical cyclone that rapidly weakens upon landfall
- A mid-latitude cyclone whose central pressure drops at least 24 mb in 24 hours (Correct answer)
- An upper-level low that separates from the main jet stream
- A rapid increase in sustained winds within a tropical storm
Correct answer: A mid-latitude cyclone whose central pressure drops at least 24 mb in 24 hours
Explosive cyclogenesis, or 'bombogenesis,' occurs when a mid-latitude low deepens by 24 mb or more in 24 hours (adjusted for latitude), producing rapidly deteriorating weather.
Question 2: What is 'wind shear' and why is it a critical aviation weather concern?
- Steady winds above 50 knots at flight altitude that increase fuel consumption
- A change in wind speed or direction over a short distance, which can cause sudden aircraft attitude changes and loss of lift (Correct answer)
- Turbulence caused by jet stream proximity above 30,000 feet
- Crosswind components exceeding runway limits at airports
Correct answer: A change in wind speed or direction over a short distance, which can cause sudden aircraft attitude changes and loss of lift
Wind shear is a rapid change in wind velocity (speed or direction) over a small area; low-level wind shear near airports is especially dangerous during takeoff and landing because it causes sudden airspeed and lift loss.
Question 3: The primary cause of most US hurricane-related fatalities in recent decades has been which hazard?
- High winds
- Storm surge and inland flooding (Correct answer)
- Tornadoes spawned by the storm
- Lightning from outer bands
Correct answer: Storm surge and inland flooding
Freshwater flooding from rainfall and coastal inundation from storm surge account for the majority of US hurricane deaths, surpassing direct wind casualties.
Question 4: What is a 'flash flood watch' versus a 'flash flood warning'?
- Watch means flooding is occurring now; warning means conditions are possible
- Watch means conditions are favorable for flash flooding to develop; warning means flash flooding is imminent or occurring (Correct answer)
- Watch covers a larger geographic area; warning is issued nationally
- Watch applies only to rivers; warning applies to urban areas
Correct answer: Watch means conditions are favorable for flash flooding to develop; warning means flash flooding is imminent or occurring
A flash flood watch indicates that conditions are favorable for rapid flooding to develop, while a warning means flash flooding is imminent or already happening and immediate action is needed.
Question 5: How does 'freezing rain' differ from 'sleet' (ice pellets) in terms of atmospheric structure?
- Freezing rain falls from clouds below freezing; sleet falls from clouds above freezing
- Freezing rain passes through a warm layer and refreezes on contact with below-freezing surfaces; sleet refreezes completely before reaching the ground (Correct answer)
- Sleet is larger than freezing rain droplets; freezing rain is microscopic
- There is no physical difference — both are solid ice when they hit the ground
Correct answer: Freezing rain passes through a warm layer and refreezes on contact with below-freezing surfaces; sleet refreezes completely before reaching the ground
In freezing rain, a warm layer aloft melts snow to rain, but a shallow subfreezing layer near the surface keeps the ground below 32°F so the drops freeze on contact; sleet refreezes into ice pellets while still aloft.
Question 6: What is a 'microburst' and how is it different from a 'macroburst'?
- A microburst covers an area less than 4 km across; a macroburst covers an area greater than 4 km (Correct answer)
- A microburst has faster winds; a macroburst has slower but longer-duration winds
- A microburst is associated only with dry thunderstorms; a macroburst only with wet thunderstorms
- A microburst is a rotating downdraft; a macroburst is straight-line
Correct answer: A microburst covers an area less than 4 km across; a macroburst covers an area greater than 4 km
A microburst is a concentrated downburst with an outburst diameter of less than 4 km lasting 2–5 minutes, while a macroburst covers more than 4 km and can last up to 30 minutes.
CBM CBM Severe Weather and Hazardous Conditions 2
What is 'explosive cyclogenesis' (commonly called a 'bomb cyclone')?