loco 41-44

Moisture is added to air by

• sublimation and condensation. 

• evaporation and condensation. 

• evaporation and sublimation.

• Rain

Answer explanation

As water changes from one state to another, an exchange of heat takes place. These changes occur through the processes of evaporation, sublimation, condensation, deposition, melting, and freezing. However, evaporation and sublimation are the only ways water vapor is added into the atmosphere.

If the temperature is 64°F (and if the temperature/dewpoint spread is too small and decreasing), what type of weather is most likely to develop?

• Fog or low clouds 

• Freezing precipitation 

• Thunderstorms

• Rain

Answer explanation

Fog typically occurs when the temperature of air near the ground is cooled to the air’s dew point. Remember, the dew point is the temperature at which the air will have 100% humidity -- it’s fully saturated with water vapor. At this point, the water vapor in the air condenses and becomes visible in the form of fog.

The amount of water vapor which air can hold depends on the

• air temperature. 

• dewpoint. 

• stability of the air.

• pressure

Answer explanation

The dew point, given in degrees, is the temperature at which the air can hold no more moisture, so it’s at 100% humidity.

Low-level turbulence can occur (and icing can become hazardous) in which type of fog?

• Rain-induced fog 

• Steam fog 

• Upslope fog

• downslope fog

Answer explanation

Steam fog is common over bodies of water during the coldest times of the year, and because of that, it’s also known as sea smoke. Steam fog forms when cold, dry air moves over warm water. As the water evaporates, it rises and resembles smoke. Low-level turbulence can occur (and icing can become hazardous) with the presence of steam fog.

Radiation fog will most likely form when

• there is warm, moist air over low, flatland areas on clear, calm nights. 

• moist, tropical air moves over cold, offshore water. 

• cold air moves over much warmer water.

• moist, warm air moves over much colder water.

Answer explanation

Radiation fog typically forms in low-lying areas like a mountain valley. Radiation fog happens when the surrounding air reaches its dew point, and the ground cools rapidly due to terrestrial radiation, caused by naturally radioactive materials on Earth including uranium, thorium, and radon. It’ll form on clear nights, with relatively little to no wind present.

The temperature and dew point are each forecasted to be 10°C. What weather should you expect?

• Strong wind 

• Freezing rain

• Fog or low clouds

• Thunderstorm

Answer explanation

Fog typically occurs when the temperature of air near the ground is cooled to the air’s dew point. Remember, the dew point is the temperature at which the air will have 100% humidity -- it’s fully saturated with water vapor. At this point, the water vapor in the air condenses and becomes visible in the form of fog.

In the remarks section of the METAR for Midway Airport,

• Rain below 3500 ft. 

• Mist below 3500 ft. 

• Rain began at 35 minutes past the hour.

• Rain will last for 35 minutes

Answer explanation

The remarks section of a METAR report always begins with the letters “RMK.”

RMK RAB35 means remarks: rain began at 35 min. past the hour (1235 UTC).

The wind direction and velocity at KJFK is from

• 180° true at 4 knots. 

• 180° magnetic at 4 knots. 

• 040° true at 18 knots.

• 020° true at 18 knots.

Answer explanation

At KJFK, the wind direction and velocity are being indicated by 18004KT. Remember that the first three numbers indicate the direction from which the wind is blowing to the nearest ten degrees in relation to TRUE north, in this case 180° true. The second two numbers indicate the speed of the wind in knots, in this case 4 knots.

What are the wind conditions at Wink, Texas (KINK)?

• Calm 

• 110° at 12 knots, gusts 18 knots 

• 111° at 2 knots, gusts 18 knots

• 25° at 17 knots

Answer explanation

At KINK, the wind direction and velocity are being indicated by 11012G18KT. Remember that the first three numbers indicate the direction from which the wind is blowing to the nearest ten degrees in relation to TRUE north, in this case 110° true. The second two numbers indicate the speed of the wind in knots, in this case 12 knots.

The “G” stands for gusting, so in this case we have reported wind gusts up to 18 knots.

In the TAF for KMEM, what does "SHRA" stand for?

• Rain showers 

• A shift in wind direction is expected 

• A significant change in precipitation is possible

• sheering wind

Answer explanation

The TAF utilizes the same descriptors and abbreviations as used in the METAR report.

Please know that you 1) you won’t be able to bring in the METAR / TAF glossary we include in this course with you into the Aeronautical Knowledge Test;  2) you do not need to memorize everything that’s in this glossary. We’ve included everything as a means of being thorough, but here are the codes that we specifically want to call out. These are the ones that tend to show up.

BKN = broken

OVC = overcast

BR = mist

SH = showers

RA = rain