Weather Flashcards
Weather should be studied and learned
systematically and thoughtfully to accrue lifelong knowledge
AND
as if my life will depend on it
Altitude is defined as the _____ and is displayed in the cockpit by an instrument called an ____
height above a given reference
altimeter
Barometric altimeter
calibrated to display altitude in feet, as opposed to pressure in inches of mercury
What kind of altitude is displayed on an altimeter?
True altitude (MSL)
When flying from one location to another at a constant indicated altitude, you’re flying along a surface of constant?
Pressure
When flying from one locale to another, a change in pressure of 1.0 inHg changes the altimeter reading
1000 feet
How can you maintain a more constant AGL altitude when flying?
Updating the reference of the altimeter setting
If you fly from an area of high pressure to an area of low pressure without changing your altimeter, what happens to your altitude?
You would have to descend to maintain a constant indicated altitude (i.e. be lower than you think you are).
“High to Low, Look Out Below”
If you fly from an area of low pressure to an area of high pressure without changing your altimeter, what happens to your altitude?
You would end up higher than your altimeter is reading.
“Low to High, Plenty of Sky” or “Low to High, Clear the Sky”
Does temperature deviations impact the altimeter?
Yes. Since altimeters are calibrated for a standard lapse rate, an incorrect indication results if the temperature deviates from the standard. For every 11 °C the temperature varies from the standard, there is a 4% altimeter error
If the air is cooler than the standard atmosphere, the aircraft is ____ than the altimeter indicates.
Lower
If the air is warmer than the standard atmosphere, the aircraft is ____ than the altimeter indicates.
higher
Define indicated altitude
altitude as read on the altimeter
Define absolute altitude
altitude is the aircraft altitude above the ground (AGL)
Define true altitude
altitude referenced to mean sea level (MSL)
Define pressure altitude
altitude above a standard datum plane (29.92 inches of mercury)
Define density altitude
pressure altitude corrected for nonstandard temperature deviations. DA is not a height reference, but rather is an indication of aircraft performance
What is the percentages of the atmosphere?
78% nitrogen, 21% oxygen, and a 1% mixture of 10 other gases
Although the atmosphere appears relatively clear, it contains
nongaseous substances such as dust, salt particles, pollen, and others. These appear as haze and cause reduced visibility
Height of the troposphere
Surface to…
55,000 feet at equator
28,000 feet at the poles
36,000 feet over United States
What layer does nearly all weather take place in?
Troposphere (b/c of large amounts of moisture and condensation)
What is the temperature like in the troposphere?
What about winds?
Temperature normally decreases with altitude (lapse rate)
Winds generally are light near the Earth’s surface and increase with altitude
What is the tropopause?
a transition zone between the troposphere and stratosphere
What is the height of the tropopause over the United States?
About 36,000 MSL
What is the temperature like in the Tropopause?
What does that produce?
The temperature in the tropopause is constant with altitude and is normally the coldest area in the lower atmosphere. As a result, contrails form and persist there.
What are the winds like in the Tropopause?
The strongest winds, those of the jet stream, occur just below the tropopause, resulting in moderate to severe turbulence. A haze layer with a definite top is also frequently found here.
What is the stratosphere and what altitude is it located at?
Above the tropopause is the stratosphere which is characterized by increasing temperature (inversion) as altitude increases, to approximately 66,000 feet.
What is flying generally like in the Stratosphere?
Since the air in the stratosphere is thin and offers little resistance, flying at this level is generally smooth with excellent visibility.
What is the standard temperature lapse rate?
The standard lapse rate is 2 °C per 1000 feet, although close to the surface, the rate may indicate an increase, decrease, or constant temperature when measured at increasing altitudes
What is an isothermal lapse rate?
The isothermal lapse rate indicates the temperature is constant with increasing altitude.
What is an inverted lapse rate (temperature inversion)? What are the conditions like within them?
An inverted lapse rate, also called a temperature inversion, generally occurs in the stratosphere when the temperature increases with increasing altitude. Conditions are usually stable within them.
What is atmospheric (barometric) pressure?
Atmospheric (barometric) pressure is the pressure exerted on the surface by the atmosphere due to the weight of a column of air directly above that surface
What is the average weigh of air on a square inch of Earth’s surface at sea level?
14.7 pounds
How does pressure vary with altitude?
Unlike temperature, pressure always decreases with altitude. In the lower layers of the atmosphere, pressure decreases more rapidly than at higher altitudes because air density decreases as altitude increases.
What two units are used to measure atmospheric pressure?
inches of mercury (inHg) and millibars (mb)
What is the difference between inHg and mb?
Inches of mercury is the measure of the height of a column of mercury that can be supported by atmospheric pressure. The millibar is a direct measure of pressure, defined by force per unit area.
What is the range for normal sea level pressures?
28 inHg (about 960 mb) to 31 inHg (about 1060 mb)
What is a standard day at sea level? (4 things)
Pressure in 29.92 inHg
Temperature is 15 ºC
Lapse rate is 1 inHg/1000’
Lapse rate is 2 ºC/1000’
What is station pressure?
Station pressure is the atmospheric pressure measured directly at an airfield or other weather station
What is sea level pressure?
Sea level pressure is the pressure that would be measured from the existing weather if the station were at mean sea level (MSL)
It can be measured directly at sea level or calculated if the station is not at sea level using the standard pressure lapse rate
What is an isobar?
Lines of equal (sea level) pressures on a surface analysis chart
How are high pressure areas depicted on a surface analysis chart?
What about low pressure
Blue “H”
Red “L”
What do ridges v. troughs indicate on a surface analysis chart?
Ridges = high pressure and good weather
Troughs = low pressure and bad weather
With a pressure change of 1.0 inHg, how many feet will the altimeter reading change?
1000
If the air is colder than the standard atmosphere, the aircraft will be __________ than the altimeter indicates.
lower
In which atmospheric layer does weather normally occur?
Troposphere
The stratosphere is characterized by smooth flying conditions and excellent
visibility
What is the standard sea level temperature in degrees Celsius (°C)?
15
What is the standard temperature lapse rate of the atmosphere in °Celsius per 1000 feet?
2.0
The average weight of air on a square inch of the Earth’s surface at sea level under standard conditions is __________ pounds.
a. 14.7
Standard sea level pressure is 1013.2 mb or __________ inHg
29.92
The height of an aircraft above the ground is known as __________ altitude
a. absolute
For every 11 °C the temperature varies from the standard, there will be a __________% altimeter error.
4
Wind direction is always expressed in terms of
direction FROM which the wind is blowing
What are station models used for?
Station models depict wind direction and speed by use of a stick with barbs and pennants
What does the alignment of the stick mean on a station model?
The alignment of the stick indicates the direction the wind is blowing from in relation to TRUE NORTH
Are the following sources reported in relation to true north or magnetic?
Charts
Reports
Station Models
ATIS
Tower
RSU
True
True
True
Magnetic
Magnetic
Magnetic
What do the barbs and pennants indicate on a station model?
Wind speed
Pennant = 50 knots
Single barb = 10 knots
Half barb = 5 knots
How current is the mb and pressure change reported on a station model?
+/- 3 hours
What other information, besides winds, does a station model provide?
Present weather and sky cover, including temperature, present weather, dew point, and sky cloud coverage
Current pressure in mb and pressure change (± in last 3 hours)
Surface Charts and Winds
How do winds flow around high pressure areas?
Clockwise around high pressure
How do winds flow around low pressure areas?
Counterclockwise around low pressure
What does the spacing of isobars depict?
The spacing of isobars shows the rate of pressure change over a horizontal distance. Pressure changes more rapidly when isobars are more closely spaced. The rate of change in a direction perpendicular to the isobars is called the pressure gradient, and the isobar spacing represents the size of the pressure gradient force (PGF)
What is the initiating force for all winds?
The pressure gradient force (PGF)
Atmospheric circulation moves air by means of ascending and descending currents. What happens when air descends?
the downward force creates a high–pressure system on the surface. The air then spreads out and diverges producing horizontal flow, or wind.
Atmospheric circulation moves air by means of ascending and descending currents. What happens air moves upward?
Low-pressure system at the surface. Air tries to converge toward the center of this low–pressure area and produces wind.
How does Coriolis force affect wind direction?
This force diverts air to the right with respect to its initial direction of motion, regardless of whether the air is near a high or a low pressure system.
Where is Coriolis force strongest?
Above 2000 feet AGL (gradient winds)
Below 2000 feet AGL, friction reduces the speed of the wind
What direction do surface winds blow?
Across the isobars from high pressure to low pressure at a 45º angle
Where is wind speed the greatest? What layer of the atmosphere?
Wind speeds generally increase with height through the troposphere, reaching a maximum near the tropopause, and culminating in the jet stream
What is the average heigh of the jet stream and what is the average wind speed?
30,000 feet
100-150 knots
What flying direction in the jet stream requires more fuel consumption?
Westbound
What are local winds?
systems ranging from tens of miles across to long, geographically thin areas. These systems are created by mountains, valleys, and bodies of water
How are sea breezes produced? How do these breezes change between daytime and night?
Land is usually warmer than bodies of water during the day, and colder at night. In coastal areas, he pressure over land is lower and that over water is higher, causing the cooler air over water to move toward the lower pressure over land. This results in a sea breeze coming from the sea. At night, the pattern reverses and air moves from land to the sea. This should be considered for takeoff and landings near the coast
What is the difference between valley winds and mountain winds? How do they form?
During the day, mountain slopes are warmed by the sun and heat the adjacent air through conduction. Cool air settles downward toward the valley floor forcing warm air up the mountain. Since the air is flowing out of the valley, its called valley wind. At night, the air in contact with the slope is cooled by terrestrial radiation becoming denser. The denser air flows downhill and is called a mountain wind.
Low pressure results from __________ air.
ascending
What is the initiating force for all winds?
Pressure Gradient Force
The jet stream is the narrow band of strong winds found below the
tropopause
A half barb on a station model on a Winds-Aloft chart is equal to __________ knots
5
On a Surface Analysis Chart, the pressure systems mentioned are outlined by isobars drawn at __________- millibar intervals.
4
A strong pressure gradient force means a __________ wind speed.
faster
Jet Stream wind speeds average about __________ knots but can reach speeds in excess of __________ knots.
100 – 150; 250
Wind that is formed from denser air that flows downhill is called a
mountain wind
As water changes from one state to another, it releases (or absorbs) ___ to (or from) the atmosphere.
heat
Air can hold only a certain amount of water depending on the air temperature. The higher the temperature, the ____ water vapor the air can hold
higher temp = more water vapor
What is saturation?
Air reaches saturation when it contains the maximum amount of water vapor it can hold for a particular temperature
What is the dew point temperature?
the temperature at which saturation occurs and is a direct indication of the amount of moisture in the air
The higher the dew point, the ____ the chance for clouds, fog, or precipitation.
greater
What is dew point depression (i.e. dew point spread)?
The difference between the air temperature and the dew point temperature.
The dew point can never be higher than the air temperature, only equal to or less than.
What is relative humidity?
the percent of saturation of the air, or the percentage of water vapor in the air compared to the maximum amount the air could hold at that temperature
What are the three characteristics of precipitation?
Showers
Continuous
Intermittent
What are the three types of precipitation?
Drizzle
Rain
Frozen
What are clouds and why do they form?
Clouds are condensed water vapor, either water droplets or ice crystals. They are formed when the air becomes saturated either by cooling to the dew point or through the addition of moisture
Why are knowing clouds and their types important?
Clouds give visible evidence of the motion, water content, and degree of stability of the atmosphere. Knowing cloud types can help you visualize weather conditions and recognize potential weather hazards.
What are low clouds? Hazard to flight? Turbulence? Precipitation/icing?
-Low clouds have bases that range from SFC to 6500 AGL
-Serious Hazard to flight ops
-Turbulence is none to moderate
-Precipitation is light rain/drizzle
-can produce icing which accumulates faster due to the clouds being denser
What are Middle clouds (and their prefix)? Hazard to flight? Turbulence? Precipitation/icing?
-6500 to 20,000 AGL
-“alto”
-Visibility from 1/2 mile to a few feet
-Turbulence and rain/snow/mix
-Icing is common
What are high clouds (and their prefix)? Hazard to flight? Turbulence? Precipitation/icing?
-20,000 to 40,000 AGL
-“cirro” or cirrus
-No precipitation and NOT an icing hazard
-little effect on flight ops
-moderate turbulence and limited visibility (severe turbulence in anvil cirrus…thunderstorms)
What are cumulonimbus (cb) clouds?
exceedingly dangerous thunderstorm clouds
(extreme turbulence, hail, ICING, lightning, and other hazards)
What is considered a severe thunderstorm?
If the CB cloud extends past the Tropopause
What are nimbostratus clouds?
can produce continuous rain, snow, or ice pellets. They also produce poor visibility and low ceilings with very slow clearing
How is the stability of air mass determined?
the temperature of the surrounding air mass
Lifted air that is colder than the surrounding air indicates what type of condition? What about lifted air that is warmer? Same temperature?
Colder -> Stable condition (more dense)
Warmer -> Unstable condition (less dense)
Same temperature -> Neutrally stable
What are the four methods by which air masses are lifted?
Convergence: two masses converge and force air upwards
Frontal Lifting: cold fronts moving through an area lifts the air ahead of it
Orographic lifting: mountainside pushes air up
Thermal lifting: intense solar heating
Which clouds usually indicate stable conditions? Unstable?
Stratiform -> Stable
Cumuliform -> Unstable
What flight conditions typically indicate stable conditions?
Temperature inversions, low clouds or fog, rising temps while climbing, rime icing, poor visibility, smooth turbulence, and stratus clouds
What flight conditions typically indicate unstable conditions?
Cumulus clouds, rough turbulence, good visibility, gusty winds, showery precipitation, and clear icing
What types of clouds contain numerous hazards such as severe to extreme turbulence, hail, icing, and lightning?
Cumulonimbus
Three forms of precipitation are __________, __________, and __________.
drizzle; rain; frozen
The four methods of atmospheric lifting are convergence, frontal, thermal, and
orographic
__________ defines air with the same temperature as the surrounding air after being lifted.
Neutrally stable
Air is __________ when it contains the maximum moisture possible for a given temperature.
saturated
Thermal lifting is also called __________ and is caused when cool air is over a warm surface and is heightened by intense solar heating.
convective lifting
Names of middle clouds contain the prefix
alto-.
If the CB cloud extends past the __________, it is considered a severe thunderstorm.
Tropopause
Lifted air that is warmer than surrounding air continues to rise and indicates a(n) __________ condition.
unstable
What is an air mass?
A large body of air with uniform temperature and moisture conditions in a horizontal plane (no abrupt temperature or dew point changes within the air mass at a given altitude)
In the temperate zone (above the continental United States), what air masses may prevail?
both cold and warm air may prevail almost anywhere in the temperate zone at any season
How are air masses named?
according to their moisture content, location, and temperature
(location being the most important)
What kind of air masses have a greater potential for producing clouds and precipitation?
Moist
Most importantly, the _____ of an air mass indicates its stability. _____ air masses bring stable conditions, while _____ air masses are inherently unstable.
Temperature
Warm = stable
Cold = unstable
What is a front?
an area of discontinuity that forms between two adjacent contrasting air masses. A front can be thought of as a boundary between the two air masses.
What is a surface front? What about a frontal zone? Why are they important?
Surface front: The point where a front comes in contact with the ground
Frontal zone: the area that encompasses the weather on either side of the front
Most active weather is focused along and on either side of the surface front and the frontal zone. Most aviation weather hazards are found in this area.
If the temperature is warmer after a frontal passage, what is the front named?
A warm front
Other characteristics of fronts:
-Fronts are always located in a trough of ______
-Cold fronts generally move ____ than warm fronts
-Frontal passage is usually accompanied by a ___º shift in wind direction
Low pressure
cold fronts = faster
90º shift in wind direction
What is a good indicator of frontal intensity?
Amount and rate of temperature change
Abrupt = strong front
Gradual = weak front
What happens to pressure while flying towards and away from a front? Why is this important?
As a front approaches or a pilot flies toward a front, pressure decreases, then rises immediately after frontal passage. Because of this pressure change, it is extremely important to obtain a valid altimeter setting when flying in the vicinity of a front.
What dangers do fronts pose in respect to winds?
Frontal passage is accompanied by a wind shift, sometimes severe. Frontal wind shifts can create hazardous wind shears in the vicinity of an airfield
What clouds usually produce steady precipitation and little to no turbulence? What clouds usually bring showery precipitation and turbulence?
Stratiform = steady and no turbulence
Cumuliform = showery and turbulence
What is the slope of the front? How do steep slopes compare to shallow slopes?
slope of the front is the ratio of vertical rise to horizontal distance
shallow front = extensive cloudiness with steady precipitation
steep slopes = rapid moving, narrow band showery, severe weather
How does the speed of a front effect its characteristics?
Faster moving fronts are generally accompanied by a narrow band of more severe weather, while slower moving fronts have less severe weather, but the frontal zone is more extensive.
The greater the contrast in the _____ and ______ between the two air masses, the greater the possibility of weather associated with a front, particularly severe weather.
temperature and moisture
What type of front creates the steepest frontal slope?
Cold front
As a cold front wedges under a less denser warm air mass, what happens?
the cold air pushes the warm air upward, this lifting creates unstable conditions, producing sometimes very violent conditions, including strong thunderstorms and severe turbulence.
How do winds shift with cold fronts? As the cold front approaches what happens to wind speed and barometric pressure?
wind shifts approximately 90° from SW to NW
Generally, as the front approaches, wind speed increases and barometric pressure decreases (lower cloud bases + rain/snow)
What is a squall line and how are they indicated on a surface chart?
A squall line is a line of violent thunderstorms. They are indicated on surface charts by a dashed, double–dotted purple line.
How many miles ahead of a cold front do squall lines develop? How are squall lines positioned relative to the cold front?
Squall lines usually develop 50 to 300 miles ahead of the cold front, and roughly parallel to it, although sometimes they can be located nowhere near a cold front.
Why are squall lines important to aviation?
Squall lines are a severe hazard to aviation. It is often impossible to fly though a squall line, even with radar, due to the storms being extremely close to one another.
What properties are used to locate and classify fronts?
Temperature, dew point, pressure, wind
What parameters of an air mass are generally uniform when measured across a horizontal plane?
Temperature and moisture
How do the winds shift during a cold front passage?
SW to NW
Squall lines generally develop where?
50 – 300 miles ahead of the cold front
What parameters of an air mass are generally uniform when measured across a horizontal plane?
Temperature and moisture
A line of violent thunderstorms that forms ahead of a cold front is known as a
squall line
Every front is located in a
low pressure trough.
Which frontal system has a steeper slope?
A cold front.
What do warm fronts create?
a broad area of cloudiness, steady precipitation, and reduced visibility
How far out do warm fronts effect?
500-700 miles
A warm front typically moves at a ____ speed than a cold front and produces a more ____ frontal slope, sloping forward and ahead of the surface front. Because of these factors, warm fronts are not as well ____ as cold fronts
slower
gradual slope
NOT as well defined
How do winds shift from a warm front?
SE to SW
What is a stationary front?
the frontal border between air masses shows little or no movement, with neither air mass replacing the other
How does a stationary front impact winds?
Surface winds along a stationary front tend to be parallel on both sides of the front rather than against or away from it. Thus, a stationary front has a 180° wind shift