14 Nebraskaland • July 2021
IN THE FIELD
By Martha Shulski
THE RAIN THAT NEVER HAPPENED
You may have noticed optically thin features
that streak downward from the base of clouds and
curve or hook to nearly horizontal. What you are
witnessing is water that fails to reach the ground.
Sometimes raindrops or ice crystals that exit a
cloud submit to the sky and evaporate or sublimate.
This is called virga.
This phenomenon is more common in the arid
climate of western Nebraska than in the humid
east. Dryness and warmth help to vaporize the
precipitation. Most often they are seen from mid-
level clouds or high-base cumuliform clouds.
As these droplets or crystals turn to vapor, they
can sometimes lead to a strong but short-lived
downdraft. Therefore, you may feel a rush of cool air
while in the vicinity of virga.
RADAR (radio detection and ranging) imagery
can be fooled into thinking these droplets
are precipitation and show a signature as
such. Researchers have found that vaporizing
precipitation is more than 30% in the world's major
deserts and accounts for half of falsely detected
precipitation in these areas.
While virga percentages are not that high here in
Nebraska, be on the lookout for the rain that never
happened.
Martha D. Shulski, at the University of Nebraska-
Lincoln, is the director of the Nebraska State Climate
Office.
Virga over the Missouri River at Niobrara State Park. BROOKE TALBOTT, PLATTE BASIN TIMELAPSE
