Weather Flashcards
How does the air flow in regard to high or low pressure systems in the northern hemisphere
High pressure - outward, downward, clockwise
Low pressure - inward, upward, counterclockwise
PHAK 12-7
What kind of weather can you expect in a low-pressure system versus a high-pressure system.
Low pressure system - characterized by rising air, which is conductive to cloudiness, precipitation and bad weather.
High-pressure system - characterized by descending air which tends to favor dissipation of cloudiness and good weather.
PHAK 12-7
Describe the different types of fronts.
Cold - occurs when a mass of cold dense, and stable air advances and replaces a body of warmer air.
Occluded - occurs when a fast-moving cold front catches up with a slow-moving warm front. Two-types: cold front occlusion and warm front occlusion
Warm - The boundary area formed when a warm air mass contacts and flows over a colder air mass.
Stationary - When the forces of two air masses are relatively equal, the boundary or front that separates them remains stationary and influences the local weather for days. The weather is typically a mixture of both warm and cold fronts.
PHAK 12-18
What kind of weather can you expect in a cold front versus a warm front?
Cold - As the front passes, expected weather can include towering cumulus (intermediate) or cumulonimbus (intense), heavy rain accompanied by lighting, thunder and/or hail; tornadoes possible; during passage poor visibility, winds variable and gusting; temperature/dew point and barometric pressure drop rapidly.
Warm - As the front passes, expected weather can include stratiform clouds, drizzle, low ceilings and poor visibility; variable winds; rise in temperature
Note: the weather associated with a front depends on the amount of moisture available, the degree of stability of the air that is forces upward, the slope of the front, the speed of frontal movement, and the upper wind flow.
PHAK 12-18
What is a trough
An elongated area of low pressure system
PHAK 12-12
What is a ridge
An elongated are of high pressure system
PHAK 12-12
What are the standard temperature and pressure values for sea level
59 °F or 15 °C and a surface pressure of 29.92 inches of mercury (“Hg) or 1,013.2 mb
PHAK 4-3
What are isobars
Isobars are lines drawn on a weather chart to depict lines of equal pressure.
PHAK 12-12
What happens if the isobars are relatively close together versus widely spaced.
Close together - a steep pressure gradient exists which indicates higher wind speeds.
Widely spaced - a shallow pressure gradient usually means wind speeds will be less.
PHAK 12-12
What causes the winds aloft to flow parallels to the isobars.
Coriolis force.
PHAK 12-4
Why fo surface winds generally flow across the isobars at an angle.
Surface friction.
At what rate does the atmospheric pressure decrease with an increase in altitude.
Standard pressure lapse rate is 1” Hg per 1000 feet.
PHAK 4-3
What does “dew point” mean.
The temperature to which a sample of air must be cooled to attain the state of saturation.
When the temperature of the air is reduced to the dew point, the air is completely saturated and visible moisture begins to condense out of the air in the form of fog, dew, frost, clouds, rain, or snow
PAHK 12-13
What factor primarily determines the type and vertical extent of clouds.
The stability of the atmosphere.
What is the difference between a stable atmosphere and an unstable atmosphere. Why is the stability of the atmosphere important.
The stability of the atmosphere depends on its ability to resist vertical motion. A stable atmosphere makes vertical movement difficult, and small vertical disturbances dampen out and disappear.
In an unstable atmosphere, small vertical air movements tend to become larger, resulting in turbulent airflow and convective activity.
Instability can lead to significant turbulence, extensive vertical clouds, and severe weather.
PHAK 12-12
