Weather Information Flashcards
State the general characteristics in regard to the flow of air around high and low pressure systems in the N. hemisphere
Low Pressure - inward, upward, and counterclockwise
High Pressure - outward, downward, and clockwise
If your route of flight takes you toward a low-pressure system, in general what kind of weather can you expect? What if you were flying towards a high-pressure system
A low-pressure system is characterized by rising air, which is conductive to cloudiness, precipitation, and bad weather. A high-pressure system is an area of descending air which tends to favor dissipation of cloudiness and good weather
Describe the different types of fronts
Cold front - occurs when a mass of cold, dense, and stable air advances and replaced a body of warmer air
Occluded front - A frontal occlusion 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 front - The boundary are formed when a warm air mass contact and flow over a cold air mass
Stationery front - When the force of two air masses are relatively equal, the boundary or front that separate them remains stationary and influence the local weather for days. The weather is typically a mixture of both warm and cold fronts
What are the general characteristics of the weather a pilot would encounter when operating near a cold front and a warm front?
Cold Front - As the front passes, expected weather can included towering cumulus or cumulonimbus, heavy rain accompanied by lightning, thunder and/or hail; tornadoes possible; during passage, poor visibility, winds variable and gusting; temp/dew point and pressure drop rapidly
Warm Front - As the front passes expected weather can included stratiform clouds, drizzle, low ceilings, and poor visibility; variable winds; rise in temp
What is a trough
A trough, called a trough line, is an elongated area of relatively low atmospheric pressure. At the surface when air converges into a low, it cannot go outward against the pressure gradient, nor can it go downward into the ground; it must go upward. Therefore, a low or trough is an are of rising air. Rising air is conductive to cloudiness and precipitation; hence the general association of low pressure and bad weather
What is a ridge
A ridge, also called a ridge line, is an elongated area of relatively high atmospheric pressure. Air moving out of a high or ridge depletes the quantity of air; therefore, these are areas of descending air. Descending air favors dissipation of cloudiness; hence the association of high pressure and good weather
What are the standard temp. and pressure values
15 degrees C 29.99” Hg
What are isobars
An isobar is a line on a weather chart which connects areas of equal or constant barometric pressure
If the isobars are relatively close together on a surface weather chart or a constant pressure chart, what information will this provide
The spacing of isobars on these charts defines how steep or shallow a pressure gradient is. When isobars are spaced very close together, a steep pressure gradient exists which indicates. higher wind speeds. A shallow pressure gradient usually means win speed will be less
What causes the winds aloft to flow parallel to the isobars
The Coriolis force
Why do surface winds generally flow across the isobars at an angle
Surface friction
At what rate does atmospheric pressure decrease with an increase in altitude
1” Hq per 1,000 Feet
What does dew point mean
Dew point is the temperature to which a sample of air must be cooled to attain the state of saturation
When temperature and dew point are close together, within 5 degrees, what type of weather is likely
Visible moisture in the form of clouds, dew, or fog. Also, these are ideal conditions for carburetor icing
What factor primarily determines the type and vertical extent of clouds
The stability of the atmosphere
Explain 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 disturbance dampen out and disappear. In an unstable atmosphere, small vertical air movement tend to become larger, resulting in turbulent airflow and convective activity. Instability can lead to significant turbulence, extensive vertical clouds, and sever weather
List the effects of stable and unstable air on clouds, turbulence, precipitation and visibility
Stable: Clouds: Stratiform Turbulence: Smooth Precipitation: Steady Visibility: Fair to Poor
Unstable Clouds: Cumuliform Turbulence: Rough Precipitation: Showery Visibility: Good
When significant precipitation is occurring at the surface, how thick can you expect the clouds to be?
Significant precipitation usually requires clouds to be at least 4,000 feet thick. The heavier the precipitation, the thicker the clouds are likely to be
During your preflight planning, what type of meteorological information should you be aware of with respect to icing
Location of fronts - A front’s location, type, speed, and direction of movement
Cloud layers - The location of cloud bases and tops, which is valuable when determining if you will be able to climb above icing layers or descend beneath those layers into warmer air; reference PIREPs and area forecasts
Freezing levels - Important when determining how to avoid icing and how to exit icing conditions if accidentally encountered
Air temperature and pressure - Icing tends to be found in low-pressure areas and at temperatures at or around freezing
What is the definition of the term freezing level and how can you determine where that level is?
The freezing level is the lowest altitude in the atmosphere over a given location at which the air temperature reaches 0 degrees C. It is possible to have multiple freezing layers when a temperature inversion occurs above the defined freezing level. A pilot can use current icing products (CIP) and forecast icing products (FIP), as well as the freezing level graphics chart to determine the approximate freezing level. Other potential sources of icing information are: area forecasts, PIREPS, AIRMETs, SIGMEt, surface analysis charts, low-level significant weather charts, and wins and temps aloft
What conditions are necessary for structural icing to occur
Visible moisture and below freezing temp at the point moisture strikes the A/C
Name the main type of icing an aircraft may encounter in-flight
Structural, induction system, and instrument icing
Name the three types of structural icing that may occur in flight
Clear ice - forms after initial impact when the remaining liquid portion of the drop flow out over the A/C surface, gradually freezing as a smooth sheet of solid ice
Rime ice - forms when drops are small, such as those in stratified clouds or light drizzle. The liquid portion remains after initial impact freezes rapidly before the drop has time to spread out over the A/C surface
Mixed ice - forms when drops vary in size or when liquid drops are intermingled with snow or ice particles. The ice particles become imbedded in clear ice, building a very rough accumulation
What action is recommended if you inadvertently encounter icing conditions
The first course of action should be to leave the area of visible moisture. This might mean descending to an altitude below the cloud bases, climbing to an altitude above the cloud tops, or turning to a different course
Is frost considered to be hazardous to flight? Why?
Yes, because while frost does not change the basic aerodynamic shape of the wing, the roughness of its surface spoils the smooth flow of air, thus causing a slowing of airflow. This slowing of the air causes early airflow separation, resulting in a loss of lift. Even a small amount of frost on airfoils may prevent an aircraft from becoming airborne at normal takeoff speed. It is also possible that, once airborne, an A/C could have insufficient margin of airspeed above stall so that moderate gusts or turning flight could produce incipient or complete stalling
What factors must be present for a thunderstorm to form
Sufficient water vapor
An unstable lapse rate
AN initial upward boost (lifting) to start the storm process in motion
What are the three stages of a thunderstorm
Cumulus stage - Updrafts causing raindrops to increase in size
Mature stage - Rain at earth’s surface; it falls through or immediately besides the updrafts; lightning; perhaps roll clouds
Dissipating stage - Downdrafts and rain begin to dissipate
What is a temperature inversion
An inversion is an increase in temperature with height - a reversal of the normal decrease with height. An inversion aloft permits warm rain to fall through cold air below. Temp in the cold air can be critical to icing. A ground-based inversion favors poor visibility by trapping fog, smoke, and other restrictions into low levels of the atmosphere. The air is stable, with little or no turbulence
