METEOROLOGIST JEFF HABY
Much of the light precipitation detected on radar does not reach the ground. This is especially true
if there is a dry layer of air between the surface and from where the precipitation is falling. This is
even more especially true if the precipitation falls through a deep dry layer and the precipitation begins
the fall from high aloft. Rain falling from high aloft is very common in the
downwind portion of a
virga are common on the downwind side of a storm. When the radar beam gets high enough it
will detect these thick clouds and virga aloft. This may mislead the radar operator into thinking
precipitation is reaching the ground in those locations when it is not.
Strong winds will shear the top of a thunderstorm. This moves thick cloud, precipitation and virga
downwind from the storm. If this shows on radar as a green color it is likely not reaching the ground.
Keep the following in mind:
1. Anvil blowoff will be especially evident at long ranges from the radar since the radar beam increases
in elevation away from the radar site.
2. Anvil blowoff will generally show as light reflectivity (usually color coded green) and this
reflectivity generally does not result in precipitation reaching the ground.
3. Strong updrafts in a strong
shear environment (strong upper level wind) will often have
the anvil blowoff showing on radar.
4. Anvil blowoff tends to show up best on composite reflectivity since it is using multiple tilt angles and
showing reflectivity from all the different angles.
Here are some example of anvil blowoff from storm(s) on radar: