METEOROLOGIST JEFF HABY
A shear axis denotes a horizontal change in wind speed or direction.
Convergence will occur when horizontal
wind streams move toward one another. Strong wind speeds moving into a region of weaker wind can also do the
trick. The following can create a shear axis:
sea breeze front,
outflow boundary, secondary surge of cold air
behind cold front boundary,
dryline, trough axis, and topography.
On a surface chart, a dashed line denotes a
shear axis. What is the difference between a shear axis and a front? A shear axis does not have as well of a
defined synoptic scale
temperature gradient from one side of the axis to the other. There can be a dramatic
temperature and moisture difference on the mesoscale however. A shear axis represents a zone of convergence more
than it does a boundary between
air masses. A shear axis can be mesoscale or synoptic in size while a front is
synoptic scale in size.
Why are shear axes important?
(1) They can act as a trigger mechanism for precipitation,
(2) They can change a forecast significantly. Locating their presence is extremely important.