Air Masses & Weather Systems Flashcards
(20 cards)
Every physical process of weather is accompanied by, or is the result of….
a heat exchange
What are the basic weather systems?
Warm fronts
Cold fronts
High pressure
Low pressure
What is a front?
The front or advancing edge of an air mass that will soon replace the air mass that’s over the specific region it is moving into.
Fronts are usually accompanied by….
weather changes.
Warm Fronts
Form when warm, moist air slides up and over cold air. As it rises, it condenses into stratus type clouds which generally creates a cloud ceiling. There is generally widespread precipitation, bad visibility and low turbulence under the ceiling.
Steady precipitation preceding any front is an indication of stratiform clouds with little or no turbulence.
Turbulence is caused by
Rising air
Cold Fronts
Cold fronts form when cold air pushes under a warm air mass, forcing the warm air to rise. Thunder heads and cumulus type clouds can form as moisture in the warm air rises, cools, and condenses. Cold fronts are usually associated with poor weather as thunderstorms and showers can mature. There is moderate to high turbulence due to the rising air. Visibility is good unless there are rain showers or other kinds of precipitation. As a cold front moves through, cool and fair weather follows.
Stationary Fronts
Where both a cold front and a warm front merge. Neither front is strong enough to replace the other and the result is a stagnant merging of both fronts. The weather associated with a stationary front is typically a mixture of weather from warm and cold fronts. Pilots can expect the weather in the area to persist for several days, and the surface winds will blow parallel to the frontal zone.
Occluded Fronts
Occur when a faster moving front catches up with a slower moving front and overtakes it causing the merging of 3 air masses. There are two types of occlusions, a warm occlusion and a cold occlusion. A cold occlusion is when a cold front overtakes a warm front that is pushing into a colder mass of air. A warm occlusion is when a warm front overtakes another warm front pushing into a colder mass of air. Occluded fronts can be found with the characteristics of both warm and cold fronts. The weather is usually more tightly packed because of the merging of air masses. This causes the clouds to become over-saturated to the point where they dump water in the form of rainshowers.
Cold Occlusion
A cold occlusion is the most common because cold fronts move much faster than warm fronts. In the atmosphere, cold fronts are associated with areas of greater pressure change. Isobars in cold air masses are closer together meaning the pressure is changing more over a given distance. When pressure changes more, it drives more airflow (wind).
Squall Lines
A non-frontal, narrow band of active thunderstorms that often develop ahead of a cold front. Often form from convective updrafts in or near mountain ranges and linear weather boundaries, usually strong cold fronts or troughs of low pressure. Squall lines tend to be hundreds of miles long. Heavy rain, hail, and damaging winds can occur in a squall line.
High Pressure System
High pressure air masses bring in settled, dry weather. Cold air moving from upper layers of the atmosphere towards earth’s surface becomes more dense as it sinks and the water that’s inside it vaporizes. There is no water to form clouds and the air is stable and dry. High pressure systems rotate in a clockwise direction when in the northern hemisphere, and counter-clockwise when in the southern hemisphere. It is easy to remember high pressure system’s movement as down (from upper atmosphere), rotating clockwise and propogating outward.
Low Pressure System
Low pressure air masses bring in unsettled weather with precipitation or storms. Systems of air that rise due to warmer water or land below it. The air becomes hot and expands, becoming less dense. When there is moisture in the air mass, it weighs less as vapor than air and this causes it to rise and condense. The result is wet, less dense air that rises and cools. Low pressure systems rotate in a counter-clockwise direction in the northern hemisphere and clockwise direction when in the southern hemisphere. It is easy to remember low pressure system’s movement as up (from the surface) rotating counter-clockwise, and inward.
High Pressure is Downright Out of this World
High pressure travels down from upper atmosphere, spins right (clockwise) and propagates out. Low pressure is the opposite
Low pressure up in this b**
Low pressure travels up from lower atmosphere and propagates in, rotating left counter-clockwise
If the lapse rate increases (increased decrease in temperature with increase in altitude)…
Then the air will be more unstable
If winds of 40 knots or greater blow across a mountain ridge…
Possible mountain wave turbulence could be expected, even if the air is otherwise stable.
One positive of unstable/rising air is that it normally has good….
visibility
Characteristics of unstable air are…
Turbulence, good surface visibility, cumuliform clouds, and showery precipitation.
General Rule: Rising Air =
Bad Weather
Cold fronts force warm air up…bad weather.
Low pressure systems swirl and rise…bad weather
