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

Kinetic energy - 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 - 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