SPC Aviation Weather Information 2 — Questions and Answers
Question 1: What does a SIGMET (WS) warn pilots about?
- Severe or extreme turbulence, severe icing, or widespread dust/sandstorms (Correct answer)
- Surface wind gusts above 15 knots
- Forecast freezing levels below 5,000 feet
- Visibility reductions due to fog at destination airports
Correct answer: Severe or extreme turbulence, severe icing, or widespread dust/sandstorms
SIGMETs are issued for hazardous weather significant to all aircraft, including severe turbulence, severe icing, and widespread dust or sandstorms lowering visibility below 3 miles.
Question 2: Which weather product provides a pilot with the forecasted position of fronts, pressure centers, and precipitation for a 12 to 24 hour period?
- Constant pressure analysis chart
- Prog chart (Prognostic chart) (Correct answer)
- Surface analysis chart
- Weather depiction chart
Correct answer: Prog chart (Prognostic chart)
Prognostic (prog) charts depict forecast surface weather including fronts, pressure systems, and precipitation areas at 12- and 24-hour intervals.
Question 3: An Airport/Facility Directory (Chart Supplement) lists a rotating beacon operating during daylight hours. This indicates the airport is located in an area of:
- Class B airspace
- Instrument meteorological conditions (IMC) (Correct answer)
- Uncontrolled airspace
- Restricted area proximity
Correct answer: Instrument meteorological conditions (IMC)
A rotating airport beacon operating during daylight hours indicates that the airport is in instrument meteorological conditions (IMC) — ceiling below 1,000 feet and/or visibility below 3 miles.
Question 4: What is the standard temperature lapse rate in the International Standard Atmosphere (ISA) below 36,000 feet?
- 2°C per 1,000 feet (Correct answer)
- 3°C per 1,000 feet
- 3.5°F per 1,000 feet
- 2°F per 1,000 feet
Correct answer: 2°C per 1,000 feet
The ISA standard lapse rate is approximately 2°C (3.5°F) per 1,000 feet of altitude gain in the troposphere.
Question 5: Virga is best described as:
- Ice crystals forming at high altitudes that produce halos around the sun
- Precipitation that evaporates before reaching the ground (Correct answer)
- Fog that forms along coastlines due to warm moist air
- Rotor clouds forming in the lee of mountains
Correct answer: Precipitation that evaporates before reaching the ground
Virga is streaks or wisps of precipitation falling from clouds that evaporate in the dry air below before reaching the ground, and can be associated with strong downdrafts.
Question 6: What is the primary hazard associated with flying through an area of virga?
- Severe icing on airframe surfaces
- Unexpected strong downdrafts and microburst-like wind shear (Correct answer)
- Reduced visibility below VFR minimums
- Carburetor icing in piston engines
Correct answer: Unexpected strong downdrafts and microburst-like wind shear
Virga is associated with strong downdrafts and potential microburst wind shear because the evaporating precipitation cools and accelerates the descending air column.
Question 7: A Convective SIGMET (WST) is issued for which of the following conditions?
- Moderate turbulence between 15,000 and 25,000 feet MSL
- Severe or extreme turbulence, or a line of thunderstorms at least 60 miles long (Correct answer)
- Any convective activity within 50 miles of a Class C airport
- Thunderstorm tops above flight level 250
Correct answer: Severe or extreme turbulence, or a line of thunderstorms at least 60 miles long
Convective SIGMETs are issued for severe or embedded thunderstorms, tornadoes, hail ≥3/4 inch, or a line of thunderstorms at least 60 NM long with thunderstorms affecting at least 40% of its length.
SPC Aviation Weather Information 2
What does a SIGMET (WS) warn pilots about?