J/KG: Joules per Kilogram. These are the units for CAPE and CIN. See Cape and Cin.
Jet Max (or Speed Max, Jet Streak): a point or area of relative maximum wind speeds within a jet stream.
Jet Streak: A concentrated region within the jet stream where the wind speeds are the strongest. It sets up unique wind currents in its vicinity which either enhance or diminish the likelihood of clouds and precipitation. It will propagate downstream along the jet stream axis.
Jet Stream: A narrow band of strong winds in the atmosphere that controls the movement of high and low pressure systems and associated fronts. Jet Streams meander from time to time. Wind speeds can reach 200 mph or higher in certain cases. It is usually found at 30,000 to 40,000 feet above the earth's surface. It owes its existence to the large temperature contrast between the polar and equatorial regions. The position and orientation of jet streams vary from day to day. General weather patterns (hot/cold, wet/dry) are related closely to the position, strength and orientation of the jet stream (or jet streams). A jet stream at low levels is known as a low-level jet.
Jetty: A structure (e.g.; a pier, or mole of wood or stone) extending into a sea, lake, or river to influence the current or tide or to protect a harbor.
Jokulhlaup: An Icelandic term
meaning glacier dammed lake outburst flood.
Juvenile Water: Water formed chemically within the earth and brought to the surface in intrusive rock.