Stationary Front - A nearly stationary narrow zone of transition between contrasting air masses; winds blow parallel to the front but in opposite directions on either side of the front.

Evapotranspiration - The sum of evaporation in which water is transferred from the land to the atmosphere. This includes moisture that evaporates from the soil and other moist surfaces, as well as moisture that is taken from plants due to transpiration.

Hail-Spike - A radar signature that can occur when severe hail is present in a thunderstorm. The signature is seen as a narrow line of weak reflectivity beyond the thunderstorm. Its occurrence is due to the way the radar pulse is scattered in many directions when it reaches large hailstones. This phenomenon is also referred to as the three-body scatter spike.

Climate - The average weather conditions for a specific location during a year or for many years. This can be thought of as the prevailing weather conditions that occur for a certain location in general, or over a long period of time.

Clear Slot - In respect to severe thunderstorms, a clear slot is a local region of clearing skies or reduced cloud cover. This oftentimes indicates that there is an intrusion of drier air, oftentimes noted by a bright area with higher cloud bases on the west or southwest side of a wall cloud. A clear slot is believed to be a visual indication of a rear flank downdraft

Doppler Effect - The shift in frequency that occurs when an object goes from moving towards an observer to away from an observer. Everyone has heard this when a police car drives by. As the police car is approaching, the siren will have a high pitch. Then when the police car begins moving away from you the pitch of the siren lowers. This effect is what weather radars use to calculate velocity.

Loaded Gun (Sounding) - A description of the state of the atmosphere that is characterized by extreme instability. Loaded gun soundings contain a stable layer, called a cap, that must be broken through in order for the instability to be unleashed. If the cap is overcome, rapid development of strong to severe thunderstorms can be expected.