Severe weather can be recognized in doppler radar using either velocity characteristics or reflectivity echo morphology.  In  this section we  will focus on  reflectivity signatures.

Hail: In the following link, large hail occurred in the red or greater areas.  Very high reflectivities usually are associated with hail.
Large Hail--NWS Louisville

LEWP: Line Echo Wave Pattern--a bend within a relatively linear echo feature that points back (usually to the west).  It may be indicative of developing rotational winds in a thunderstorm; rotating thunderstorms also are known as supercells, and are associated with a mesocyclone which is the parent storm of a tornado.

 Line Echo Wave Pattern (LEWP)

LEWP, Virginia

LEWP over Arkansas (Figure from NWS COMET program)


Bow Echo:  The bow echo is a forward bulge (usually to the east) in a relatively linear echo feature.  It is a sign of very strong low-level straight-line winds, and may  indicate the presence of a  downburst or microburst. Because of the wind shear associated with the very strong straight-line winds, rotation can develop at the northern and southern tip of bow echoes; therefore these locations are sometimes associated with tornadoes.  However, the bow echo is primarily a straight-line wind signature.

Note: the online "literature" seems to contain some confusion between the bow echo and the LEWP.  They may even both be present on different parts of a linear echo.  Typically, however the "bent-back" LEWP is associated with mesocyclone rotational winds, while the bow echo is associated with straight-line winds.

Bow Echo--NWS Louisville

Bow Echo Sequences

Bow Echo/LEWP with Tornado--NWS Louisville

 Daytona Spring 2001 Bow Echo Windstorm


Hook Echo: A thin, curving , extension of a very high reflectivity feature indicative of mesocylonic rotation and potentially tornadoes.  This was the "original" tornado signature back before doppler weather radar!

Hook Echo--UMich.

 Hook Echo--Splitting Supercell Storm--NWS Louisville

 Hook Echo--Oklahoma City Tornado--Dr. Jack Beven

Leading edge gradient: A strong gradient of reflectivity on the edge of an area of strong echoes.  It is  indicative of a rapid transition between updrafts (weak or no echoes) and downdrafts (intense echoes where precipitation is reaching ground) and is a sign that the storm is severe.  There can be much turbulence associated with the close proximity of the up- and downdrafts.

WER: Weak echo region.

BWER: Bounded weak echo region.

The following slide from NWS Milwaukee summarizes some reflectivity considerations for assessing radar echos for severe weather: