The Lemon Technique (LT)
to determine updraft strength
This section deals with the Lemon Technique of severe storm detection by
radar, designed for environments with moderate to strong
vertical wind shear.
We have seen that strong shear causes weak
updrafts to slope from the vertical,
whereas stronger updrafts
are able to withstand the shear and assume a more
vertical character. The Lemon Technique, and modified versions such as the
WRIST technique, allow the radar operator to infer the strength of the updraft
through three-dimensional visualization of the radar-detectable rainy
surrounding the updraft.
We stress that the radar operator must perform the
vertical tilt sequence employed in these techniques to determine storm
structure and classification properly.
This diagram represents a weak, non-severe storm (most likely
a sheared environment. The top figure is a westward view of a vertical cross
section of the storm, whereas the bottom diagram is a horizontal, low-level
cross section. (Note line A-B in the lower figure, which corresponds to the
vertical cross section.) Precipitation and rainy downdraft descend downwind
(usually northeast) from near the summit of the tilted cloud. The radar
echo, the bottom figure, has a concentric reflectivity configuration, with the
highest top over the center of the low-level echo maximum. Note the orange
arrow, which represents the trajectory that air parcels take into the storm,
through the updraft, and out of the storm through the downwind anvil.