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WX301 EXAM; QUESTIONS AND ANSWERS
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WX301 EXAM; QUESTIONS AND ANSWERSExplain why the true state of the atmosphere can never be known exactly and can
only be approximated by assimilating all available data - ANSWER • Atmosphere
is too complex and changing constantly
• We cannot make up observations at all altitudes, places, most accurate, etc
• Our technology cannot keep up and continuously report everything that goes on
• D, all of the above
Explain the fundamental difference between ensemble forecast models and
deterministic forecast models - ANSWER • Deterministic: start with an initial state
and generate a single forecast, high-resolution
• Ensemble: utilize multiple forecasts for the same period, faster but not as good of
a forecast, forecasting the uncertainty of the forecast
3. Determine the analysis time, valid time, and forecast length given numerical
model output. - ANSWER • Given a map, on the map, know:
• time when you started collecting data (analysis time)
• ___ for Month, Day, Zulu (valid time, convert to local by subtracting 5 hours)
• How many hours between valid and analysis time (forecast length)
Identify the favored regions around a low pressure system the formation of snow
and other types of frozen precipitation - ANSWER • Snow and freezing
precipitation located to the northwest of the low, can have it north of warm front
Describe how the temperature must change with height to produce rain, snow, sleet,
or freezing. - ANSWER • Depends on thickness of the cold layer
• Rain is melted snow crystals
• In snow, crystals remain below freezing all the way to the ground
, • Freezing rain is rain that falls into shallow layer of cold surface air
• Sleet is rain that falls into deeper layer of cold surface air
Define critical thickness - ANSWER • Thickness at which air is cold enough to
snow
• Thickness is proportional to the average temperature of the layer
• Larger thickness = warmer; smaller thickness = colder
Analyze a 1000-500mb thickness chart to determine the likelihood of rain versus
snow. (Recall that the 540dam line only identifies where snow is possible, the
lower the thickness values the greater the likelihood of snow.) - ANSWER • 540dm
(decameters, height) is a good dividing line between rain and snow
Define what is meant by ground icing "hold-over" times. - ANSWER • Hold-over
time: length of time deicing fluid will prevent ice build-up on an aircraft
• Time ranges from 45 minutes for frost to less than a couple minutes for freezing
rain
Explain why equivalent liquid water precipitation rate is important in aviation
winter weather decision-making and how it affects hold-over times. - ANSWER •
Basing precipitation intensity on visibility alone does not adequately measure true
rate of liquid water equivalent accumulation
• Accurate, real-time measurements of liquid-equivalent snowfall rates need to be
made and reported to pilots and ground operations personnel, not just visibility
measurements.
• Accurately predicting deicing hold-over times remains a significant aviation
safety factor
Identify the fundamental cause of icing - ANSWER • Liquid water droplets
Identify the temperatures favorable for rime, clear and mixed icing - ANSWER •
Rime: small droplets, freeze rapidly cause trapped air, opaque appearance, forms at
temps below -15C
• Clear: larger droplets with little trapped air, forms at 0 to -5 C, equivalent to
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