III.A. Weather Theory Flashcards
Most of Earth’s weather occurs in what region of the atmosphere?
The Troposphere. Extends up to 36,000ft.
What are the standard temperature and pressure values for sea level?
15° C (59° F)
29.92 inHG (1013.2 mb)
What are isobars?
Lines of equal or constant pressure on a weather chart.
If isobars are relatively close together on a surface weather chart, what would this indicate?
The spacing defines the pressure gradient. Close together would indicate higher windspeeds.
What does dew point mean?
Dew point is the temperature to which air must be cooled to reach saturation. The air gets so full of moisture (water vapor) that it can’t hold any more.
In simpler terms: When the dew point is high, it feels more humid, or sticky, outside. When it’s low, the air feels dry.
What factor primarily determines the type and vertical extent of clouds?
Stability of the atmosphere.
Stable air resists upward movement, and unstable air would lead to more vertical development.
Explain the difference between a STABLE atmosphere and an UNSTABLE atmosphere.
STABLE: the atmosphere resists vertical movement, so disturbances dampen out or disappear.
UNSTABLE: Small vertical movements can become larger, resulting in turbulence, extensive vertical clouds and severe weather.
How can you determine the stability of the atmosphere?
When temperature decreases rapidly as you climb, you have unstable air.
When temperature remains unchanged, or decreases only slightly with altitude, the air tends to be stable.
When air near the surface is warm and moist (hot/humid) expect instability.
List the effects of STABLE air on clouds, turbulence, precipitation, and visibility.
Clouds: Stratiform
Turbulence: Smooth
Precip: Steady
Visibility: Fair to Poor
List the effects of UNSTABLE air on clouds, turbulence, precipitation, and visibility.
Clouds: Cumuliform
Turbulence: Rough
Precip: Showery
Visibility: Good
What are the general characteristics of a HIGH pressure system?
High Pressure = outward, downward, and clockwise.
What are the general characteristics of a LOW pressure system?
Low Pressure = inward, upward, counterclockwise
If your route of flight takes you toward a LOW pressure system, what kind of weather can you expect?
Generally poor. Rising air will likely produce cloudiness, precipitation, and turbulence.
If your route of flight takes you toward a HIGH pressure system, what kind of weather can you expect?
Generally good weather. Descending air favors dissipation of clouds
What are the different types of FRONTS?
Cold Front
Warm Front
Occluded Front
Stationary Front
Generally speaking, what kind of weather would you expect to encounter when flying near a COLD front?
Towering cumulus clouds
Heavy rain, Thunderstorms
Poor visibility
Variable gusty winds
Rapid drop in barometric pressure
Generally speaking, what kind of weather would you expect to encounter when flying near a WARM front?
Stratiform clouds
Low ceilings, poor visibility
Drizzle or steady rain
Rising temperature
What is a trough?
A line of low pressure, and rising air. Generally poor weather, cloudiness and rain.
What is a ridge?
A line of high pressure, and descending air. Generally good weather.
Define the term: ceiling.
Lowest overcast or broken layer.
The height above the ground at which the lowest layer of clouds or obscuring phenomena (e.g. fog, smoke) covers more than half the sky.
If the temperature is +16°C at an elevation of 1,600ft, and a standard temperature lapse rate exists, what will the approximate freezing level be?
9,600ft MSL
16° ÷ 2° (per 1,000ft) = 8
8 x 1000= 8,000ft
8,000ft (lapse to freezing) + 1,600ft (field elevation) = 9,600ft MSL
Name and explain the four types of fog.
Radiation fog (aka Ground fog)
Advection fog: warm moist air over cool water
Upslope fog: warm moist air condenses when blown up a mountain
Steam fog: very cold air moves over warmer water Upslope
What causes turbulence?
Convective currents
Mechanical (mountains, or buildings)
Wind shear
What three elements do you need for a thunderstorm to form ?
Water vapor
Unstable lapse rate
Uplifting
*Juice, heat, and lift
