ATC ACA1 Weather

Atmospheric Pressure

The force exerted by the atmosphere at a given point

Standard Atmospheric Value for surface temperature

15C/59F

Standard Atmospheric Value for surface pressure

29.92 in of Mercury/1013.2 Millibars

Weight of atmosphere at sea level

14.7 lbs per square inch

Lapse rate for pressure

1 in of mercury for every 1000ft

Lapse rate for temperature

2C/ 3.3F per 1000ft

Barometer

A device used to measure atmospheric pressure

The two types of barometers

Mercurial and Aneroid

Mercurial Barometer

More accurate barometer

Aneroid Barometer

More common barometer

What is an Altimeter Setting Indicator (ASI)?

An aneroid system used at airports to provide an altimeter setting for aircraft altimeters. The primary means of obtaining altimeter settings at terminal facilities.

What is a digital version of the Altimeter Setting Indicator called?

Digital Altimeter Setting Indicator (DASI)

Station Pressure

Pressure measured at the airport

Above ground level (AGL)

Height above the ground over which you're flying

Mean sea level (MSL)

The average height above mean sea level

True Altitude

an actual or exact altitude above mean sea level.

Indicated altitude

an altitude above mean sea level indicated on the altimeter

Altimeter Setting

the value to which the scale of pressure is set so the altimeter indicates true altitude at field elevation

High to Low; Low to High (Pressure and Temperature)

High to low look out below, Low to High eyes to the sky

Pressure Altitude

The altitude in the standard atmosphere pressure surrounding the aircraft is found

What altitude are aircraft required to use pressure altitude

18,000ft and Above

What altitude are aircraft required to use indicated altitude

Below 18,000ft

Density Altitude

The altitude in the standard atmosphere where density of the air surrounding the aircraft is found

What determines air density

Pressure, Temperature, and Humidity

High Density Altitude

Air becomes thinner, reduces aircraft preformance

Low Density Altitude

Increases aircraft performance.

Convective Current

Two surfaces heated unequally cause the uneven heating of the air above

Wind

Horizontal airflow in a convective current

Advection

Horizontal movement of wind. Can transfer heat or atmospheric properties from one area to another.

Circulation

Air flow from areas of higher pressure to areas of lower pressure

Atmospheric Circulation

A convective current on a large scale

Jet Stream

A narrow band of strong winds moving through the upper atmosphere, separates warm/cold air, creates high-level wind shear

What are isobars?

Lines drawn on weather maps to connect points of equal pressure.

What do isobars help to identify?

Organized pressure points at sea level.

What is a Low Pressure Area?

A region where pressure decreases towards the center.

What is the wind flow direction around a Low Pressure Area in the northern hemisphere?

Counterclockwise.

What type of flying conditions are associated with a Low Pressure Area?

Unfavorable flying conditions.

High pressure Area

A region where pressure increases towards the center.

What is the wind flow direction around a High Pressure Area in the northern hemisphere?

Clockwise

What type of flying conditions are associated with a High Pressure Area?

Favorable flying conditions

Clouds

Visible water vapor or ice crystals

How are Clouds classified?

Method of formation, composition, and altitude they are found.

Cumulus is Latin for what?

Accumulation or heap

What is the appearance of a cumulus?

White Billowy Appearance

What can a cumulus develop into?

Cumulonimbus, Towering Cumulus, or Cumulus Fractus

What conditions are favorable for the formation of stratus clouds?

Conditions favorable for fog (Wind 5kt or less), especially over flat terrain.

Stratus is Latin for what?

Stirnere/ To Flatten out

How is a Stratus characterized?

Stratified or layered appearance

Is a Status cloud stable or unstable?

Stable

Cirrus in Latin means what?

Lock of hair or curly

How is a cirrus cloud characterized?

Thin, featherlike appearance, high altitudes.

What are the two types of cloud subclassification?

Nimbo/Nimbus- Rain Cloud, Fractus- Broken

How are thunderstorms formed?

Air must have sufficient water vapor, be unstable, and initially undergo forced lifting

What is the life cycle of a thunderstorm?

Cumulus, Mature, Dissipating Stage

What are the 10 thunderstorm hazards? HELPWithSTILT

Hail, Effect on altimeter, Lightning, Precipitation, Wind Shear, Squall Lines, Turbulence, Icing, Low ceiling and visibility, Tornados

How do thunderstorms effect altimeters?

Pressure falls with approach of storm, rises sharply with first gust and showers, falls back to normal as the storm moves on.

What is the temperature of lightning?

30,000C/54,000F

Wind Shear

An unexpected change in wind speed and/or direction resulting in a tearing or shearing effect, can be horizontal or vertical.

Microburst

"Cloudfart", A highly localized, high speed downburst of air.

What is the size of a microburst downdraft?

Typically a diameter less that 1 mile, can extend to 2 and a half miles.

How fast does air move in microbursts?

150kts

Precipitation

Snow, drizzle, rain

Air masses

Any huge body of air whose physical properties are horizontally uniform level for level.

How are air masses formed?

When a large body of air assumes the uniform properties of temperature and moisture while resting over it's "source region"

Source Region

Large snow and ice covered polar regions, cold northern oceans, tropical oceans, and large desert areas.

Two types of air?

Stable air (smooth air and worse visibility), Unstable air (rough air and good visibility)

Fronts

A boundary or line of discontinuity separating two different air masses

What are the types of fronts?

Cold Front, Warm Front, Occluded Front, and Stationary Front

Cold Front

When cold air replaces a region occupied by relatively warmer air

Characteristics of cold fronts

Temperature and humidity decreases, pressure decreases on approach and increases after passage

What direction does wind shift in a cold front?

Clockwise, usually from southwest to northwest

How fast do slow moving cold fronts move?

15kts

How fast do fast moving cold fronts move?

25 to 30kts

Warm front

When a mass of warm air is replacing a retreating relatively colder air mass.

How fast do warm fronts move?

10kts

Characteristics of warm fronts?

Precipitation is as much as 300 miles in advance of the front, unstable

What direction does wind shift in a warm front?

Clockwise, southeast to southwest

Occluded Front

When a cold front overtakes a warm front.

Where does the most severe weather occur in an occluded front?

Most severe weather occurs within 150 miles of point of occlusion

Stationary Front

Shows little or no apparent movement

How does a stationary front effect air operations?

May greatly hamper and delay air operations by remaining in an area for several days.

What are the three types of visibility?

Horizontal Surface Visibility, Air to Air Visibility, Air to Ground Visibility

Fog

A cloud resting on the earth's surface composed of visible water droplets and/or ice particles. One of the most hazardous weather phenomena known to aviation.

Radiation/Ground Fog

Most common to ATC. Caused by cooling of the earth's surface.

What are the ideal conditions for forming Radiation/ Ground Fog?

Clear cool night, Light wind less than 5 kts, and a small spread between temp and dew point

Advection Fog

Most dangerous because it forms rapidly and covers a large area.

How is Advection Fog formed?

When warm moist air moves over colder ground or water.

Upslope Fog

Occurs when air forced up a slope cools and condenses.

Steam Fog

Forms and looks like steam, which rises and disappears into the atmosphere.

How is steam fog formed?

When the dew point is raised to the temperature of the outside air.

Frontal Fog

Warm rain falling through colder air will raise the dew point to the air temperature.

What is the max height haze can extend to?

15,000 AGL

What are the types of ice?

Clear, Rime, Mixed

What is another name for Clear Ice?

Glazed Ice

What is the temperature range associated with Clear Ice?

0 to -10C

Why is Clear Ice considered the most serious type of icing?

Because of its rapid accumulation.

What makes the removal of Clear Ice by deicing equipment especially difficult?

Its rapid accumulation.

Rime

Granular, whitish, opaque, rough deposits of ice.