Weather Flashcards
Every physical process of weather is accompanied by , or is the result of a
Heat exchange.
An exchange of heat is present in every physical process of weather. The heat exchange happens first followed by pressure differential and finally movement of air
What causes variations in altimeter settings between weather reporting points?
Unequal heating of the earths surface. The exchange involved in unequal heating of the earths surface creates pressure differentials which results in variations in altimeter setting.
What are the standard temperature and pressure values for sea level?
15 celcius and 29.92” Hg mercury
Winds at 5000’ AGL is southwesterly while the surface wind is southerly. This difference in direction is primarily due to
Friction between the winds and the surface. Winds aloft flow parallel to isobars. Winds near the ground are slowed by friction with the surface and tends to flow at an angle across isobars towards a low and away from a high.
The boundary between two different air masses is known as a
Front
Air masses often have different temperature and moisture content , and the boundary between these different air masses is called a front.
One of the most recognised discontinuities across a front is
A change in temperature.
NOt all fronts have enough moisture to produce precipitation or even clouds, but there is usually a significant temperature change across a front.
ONe weather phenomenon which will always occur when flying across a front is a change in the
Wind direction
Fronts extend from low pressure systems in the northern hemisphere, wind circulation around a low pressure area is counter clockwise . Therefore the passage through a frontal zone can always be recognized by a left crosswind shifting to a right crosswind.
What is meant by Dewpoint?
The temperature to which air must be cooled to become saturated.
When the temperature of the air cools to the dewpoint. The air will become saturated (unable to hold any more water vapour) and moisture will either condense into clouds, fog or dew) or sublimate into (frost or snow)
The amount of water vapour air can hold depends on
Air temperature.
The warmer the air the more moisture it can hold. As the air cools towards dewpoint it can hold less moisture. The amount of water vapour air can hold depends on the temperature of the air.
Clouds, fog or dew will form when.
Water vapour condenses.
Condensation refers to moisture going from gaseous state to liquid state.
What are the process by which moisture is added to unsaturated air?
Evaporation and Sublimation.
Evaporation is the process of moisture going from solid state to gaseous state. Sublimation is the process of moisture going from solid state (frost or snow) directly to gaseous state.
The suffix ‘nimbus’ used in naming clouds means
A rain cloud.
“Nimbus” means rain and is used to indicate stratus clouds, or cumulus clouds that contain rain.
Clouds are divided into four families according to their
Height range.
Clouds families are determined by their height range. Low, Middle, High and clouds with extensive vertical development.
If temperature/dew point spread is small and decreasing , and the temperature is 62 degrees F. What type of weather is most likely to develop?
Fog or low clouds since the moisture in the air is likely to condense soon
Given the following:
Airport elevation = 500 ft MSL
Temperature = 23* C
Dewpoint = 15C
Lapse Rate = 2C per 1000’
Find the approximate base of the cumulus clouds .
Clouds will form when temperature and dew point are the same.
Temperature decreases at rate of 2* C per 1000’.
Subtract dew point from temperature: 23 - 15 = 8.
Divide that by Lapse rate: 8 / 2 = 4.
Multiply 4 x 1000 to find height of cloud base above the ground 4 x 1000 = 4000.
Add field elevation to find MSL height of cloud bases. 4000 + 500 = 4500. MSL
