Task C. Weather Information Flashcards
What are the 3 main layers of the atmosphere?
Troposphere
Tropopause
Stratusphere
What causes all weather?
Heat exchange (uneven heating of the Earth’s surface)
What causes wind?
Changes/differences in pressure
What are the types of fog?
Radiation Fog
Forms at night under clear skies with calm winds when heat absorbed by the earth’s surface during the day is radiated into space. As the earth’s surface continues to cool, provided a deep enough layer of moist air is present near the ground, the humidity will reach 100% and fog will form. Radiation fog varies in depth from 3 feet to about 1,000 feet and is always found at ground level and usually remains stationary. This type of fog can reduce visibility to near zero at times and make driving very hazardous.
Advection Fog
Advection fog often looks like radiation fog and is also the result of condensation. However, the condensation in this case is caused not by a reduction in surface temperature, but rather by the horizontal movement of warm moist air over a cold surface. This means that advection fog can sometimes be distinguished from radiation fog by its horizontal motion along the ground.
Sea fogs are always advection fogs, because the oceans don’t radiate heat in the same way as land and so never cool sufficiently to produce radiation fog. Fog forms at sea when warm air associated with a warm current drifts over a cold current and condensation takes place.
Upslope Fog
Forms when light winds push moist air up a hillside or mountainside to a level where the air becomes saturated and condensation occurs. This type of fog usually forms a good distance from the peak of the hill or mountain and covers a large area.
Steam Fog
Forms when water vapor is added to the air by evaporation and the moist air mixes with cooler, relatively drier air. Steam fog forms when cold air moves over warm water. When the cool air mixes with the warm moist air over the water, the moist air cools until its humidity reaches 100% and fog forms. This type of fog takes on the appearance of wisps of smoke rising off the surface of the water.
Compare stable vs unstable air
Stable air - Calm
Characterized by: stratiform clouds, continuous precipitation, smooth air, and fair to poor visibility in haze and smoke.
Unstable air - Turbulent
Characterized by: cumulus clouds, showery precipitation, good visibility, strong surface winds
What is an air mass
A large body of air that has similar temperature and moisture properties throughout. The best source regions for air masses are large flat areas where air can be stagnant long enough to take on the characteristics of the surface below
What is a front?
The transition zone between two air masses of different density. Fronts extend not only in the horizontal direction, but in the vertical as well.
Name the 4 types of fronts. How do they look on charts and what weather is expected?
Cold Front - Leading edge of colder air that is replacing warmer air. Cold air pushes warm air up causing thunderstorms. Depicted as blue ice cream cones (triangle).
Warm Front - Leading edge of warmer air that is replacing cooler air. Depicted as red suns (bumps). Low clouds and visibility, showers.
Stationary Front - A front that is not moving. Depicted as alternating cold and warm. Bad weather for a few days.
Occluded Front - When a cold front catches up to a warm front (cold air catches up to warm air that is catching up to cold air). Combination of cold and warm front weathers: low ceilings with showers and thunderstorms embedded in the clouds. Depicted as purple triangles and bumps.
What causes turbulence?
The main causes of turbulence are:
- convective currents
- obstructions to wind flow
- wind shear
What are the 3 types of icing?
Clear - hard and glossy. Forms after initial impact gradually freezing as a smooth sheet of ice.
Rime - brittle and frost like. Forms when drops are small, initial contact freezes rapidly before it has time to spread.
Mixed - hard and rough, forms when drops vary in size or when snow is mixed in with the rain.
What is required for a thunderstorm to develop?
- Sufficient water vapor
- An unstable lapse rate
- Uplifting (to start the process in motion)
What are the stages of a thunderstorm?
Cumulus Stage - initial updrafts
Mature Stage - the beginning of falling precipitation
Dissipating Stage - large downdrafts where the storm begins to rain itself out.
What is a microburst?
A localized column of sinking air (downdraft) within a thunderstorm. Usually less than or equal to 2.5 miles in diameter.
What is the dew point?
The temperature where visible moisture will occur
What is an AIRMET?
Airmen’s Meteorological Information. Weather advisory for pilots that alerts them to potential hazards in the air.
What are the types of AIRMETs?
T - Moderate turbulence or continuous surface winds of >=30kts
Z - Moderate icing
S - IFR or mountian obscration
How long are AIRMETs valid?
6 hours (though they can be amended)
What is a SIGMET?
Significant Meteorological Information. Severe weather not associated with thunderstorms.
- Severe turbulence
- Severe icing
- Dust, sandstorms, volcanic ash
How long are SIGMETs valid?
4 hours
What is a Convective SIGMET?
Hazards associated with thunderstorms
- Surface winds greater than or equal to 50 knots.
- Hail at the surface greater than or equal to ¾ inch in diameter.
- Tornadoes.
- Embedded or severe thunderstorms expected to persist for over 30 minutes.
- Lines of thunderstorms: At least 60 miles long, with storms affecting at least 40% of the Convective SIGMET area.
- Thunderstorms producing heavy or greater precipitation affecting 40 percent or more of an area at least 3,000 square miles.
How long are Convective SIGMETs valid?
2 hours
What are PIREPs? What are the different types?
Pilot-Report - real-time report of weather conditions encountered by a pilot while airborne.
Two types:
UA - Normal
UUA - Urgent
Define “lapse rate”. What is the standard lapse rate?
Rate at which the temperature falls with increasing altitude. Standard lapse rate is 2C (3.5 F) every 1,000’.
What is adiabatic cooling?
A process of cooling the air through expansion. As air moves up slope it expands with the reduction of atmospheric pressure and cools as it expands.
Dry adiabatic lapse rate is 3*C per 1,000’
What is the Coriolis effect?
Earth rotates eastwards. So wind veers to the right (counterclockwise) in the northern hemisphere (as viewed from north pole) and to the left (clockwise) in the southern hemisphere (as viewed from the south pole).
What is a low pressure system?
An area in the atmosphere where the air pressure is lower than the surrounding areas. Typically causes air to move inward, upward, and counterclockwise.
Characterized by rising air, which is conductive of cloudiness, precipitation, and bad weather.
What is a high pressure system?
An area in the atmosphere where the air pressure is higher than the surrounding areas. Causes air to move outward, downward, and clockwise. Descending air tends to favor dissipation of clouds and good weather.
When are METARs issued and how long are they valid?
Every hour, usually at 53 minutes past the hour. They’re generally valid for an hour.
Where can you get weather information?
800-wx-brief
aviationweather.gov
