J/kg

Joules per kilogram, unit commonly used to represent CAPE and CIN.

January Thaw

A period of mild weather popularly supposed to recur each year in late January.

Jet

A fast-moving wind current surrounded by slower moving air.

Jet Max

( or Jet Streak) A point or area of relative maximum wind speeds within a jet stream.

Jet Streak

Same as Jet Max; a point or area ("streak") of relative maximum wind speeds within a jet stream.

Jet Stream

(abbrev. JSTR) Relatively strong winds concentrated in a narrow stream in the atmosphere, normally referring to horizontal, high-altitude winds. 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.

Jet Stream Cirrus

A loose term for filamentous cirrus that appears to radiate from a point in the sky, and exhibits characteristics associated with strong vertical wind shear, such as twisted or curved filaments.

Jet Wind Speed Profile

A vertical wind speed profile characterized by a relatively narrow current of high winds with slower moving air above and below. A large wind (speed) shear occurs above and below the jet axis.

Jetty

In hydrologic terms, 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

JMA

Japanese Meteorological Agency

Jokulhlaup

In hydrologic terms, an Icelandic term meaning glacier dammed lake outburst flood

JSTR

Jet Stream - Relatively strong winds concentrated in a narrow stream in the atmosphere, normally referring to horizontal, high-altitude winds. 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.

JTWC

Joint Typhoon Warning Center

Juvenile Water

In hydrologic terms, water formed chemically within the earth and brought to the surface in intrusive rock