# Glossary

cold air mass

## K-Index

a measure of thunderstorm potential based on instability, moisture content of the lower atmosphere, and the depth of the moist layer. K-index=(850 mb temperature - 500 mb temperature) + 850 mb dew point - 700 mb dew point depression

 K < 15 Thunderstorm probability near 0% K = 15-20 Thunderstorm probability less than 20% K = 21-25 Thunderstorm probability 20-40% K = 26-30 Thunderstorm probability 40-60% K = 31-35 Thunderstorm probability 60-80% K = 36-40 Thunderstorm probability 80-90% K > 40 Thunderstorm probability >90%

## Katabatic Wind

wind that is created by air flowing downhill. These downslope winds can rush down elevated slopes at hurricane speeds, but most are on the order of 12 mph or less. Some of the strongest winds form where cold winds rush downhill from an elevated plateau covered with snow and ice, so katabatic winds tend to be cool or cold.

## Kelvin Temperature Scale (K)

an absolute temperature scale in which a change of 1 Kelvin equals a change of 1 degree Celsius; 0K (absolute zero) is the lowest temperature on the Kelvin scale.

## Kelvin-Helmholtz Waves (K-H Waves)

vertical waves in the air that are associated with wind shear. When two parallel layers of air move at different speeds and in opposite directions, these waves can form. When there is enough water vapor, the waves become visible as clouds. They can appear as breaking waves and as braided patterns in radar images and cloud photos.

## KFT

thousand(s) of feet

see Hard Freeze

## Kinetic Energy (KE)

energy that a body has as a result of its motion. Mathematically, it is defined as one-half the product of a body’s mass and the square of its speed.

## Kirchhoff's Law

at a given temperature, a good absorber of a given wavelength is also a good emitter of that wavelength

## Klystron

the electronic component of the NEXRAD transmitter that generates the coherent radiation necessary for the determination of Doppler velocities. The WSR-88D typically transmits its radiation using a power of 750,000 watts. Other commercial Doppler radars sometimes use a Magnetron to generate the transmitted radiation. Magnetrons typically generate less steady patterns of radiation than do Klystrons.

## Knot (kt)

the unit of speed in the nautical system; one nautical mile per hour; it is equal to 1.1508 statute miles per hour or 0.5144 meters per second

Kentucky