AOPA Pilot Magazine - July 2024 - 87

areas that reflected radiation to stay airborne
longer. You can often climb above a
broken or scattered cloud layer and avoid
most thermal turbulence.
Mountain turbulence: Mountains
create turbulence through mechanical
means. The terrain acts as a barrier
to the prevailing wind flow. When the
winds strike the mountains, the air is
forced upward and can encounter a stable
layer and be redirected toward the surface.
Winds greater than 25 knots blowing
perpendicular to the top of the mountain
ridge are favorable for mountain
waves to develop. Lenticular clouds are a
visual clue for pilots that mountain waves
exist. Rotor clouds are often associated
with the most intense turbulence. These
rotors can result in vertical currents
at 2,000 feet a minute. Extreme turbulence
near mountains can be especially
dangerous for pilots inexperienced in
mountain flying.
Frontal turbulence: Fractus clouds
that look like cloud fragments are found
under the cloud base. They are sheared by
strong winds, giving them a ragged appearance
on the bottom of the clouds. These
clouds are a visual sign of a rough ride.
Wind shear-related turbulence:
This type of turbulence is most common
in the flight levels where turbine-powered
aircraft spend most of their time.
Wind shear is defined as a change in wind
speed or direction over a short distance
and can occur either horizontally or vertically.
You will often notice the ride will
get bumpy when winds shift direction
quickly. Another visual cue to velocity
related wind shear between two layers is
Kelvin-Helmholtz waves. These waves are
characterized by their appearance similar
to ocean waves.
For those with glass panels in the
cockpit, you may have noticed this with
the wind indicator on the primary flight
display. A common example of this
change is transitioning from a headwind
to a tailwind. Wind-shear-related turbulence
often occurs near the jetstream
and around temperature inversions.
This is an area where the temperature
increases with altitude.
Clear air turbulence (CAT): This
turbulence is typically found at altitudes
above 15,000 feet. CAT occurs most frequently
during the winter months when
the jetstream is much stronger. This type
of turbulence can be among the most challenging
to avoid. Understanding that the
depth of the turbulence is usually around
2,000 feet gives the pilot some insight on
altitude changes, which can help improve
the ride conditions.
Thunderstorm-related turbulence:
The updrafts and downdrafts associated
with thunderstorms can result in loss of
Thunderstorms have been
known to produce extreme
turbulence as far as 20
nautical miles from the
parent storm. Request a wide
deviation from air traffic
control to give yourself and
your passengers some
added protection.
aircraft control to structural damage. This
is why thunderstorms must be avoided at
all costs. Do not fly under thunderstorms
even if the visibility is good. The extreme
nature of the convection within a thunderstorm
can send an aircraft on a wild
ride at 6,000 feet per minute. The worst
of thunderstorm-related turbulence usually
happens between 10,000 and 20,000
feet. As expected, the worst storms are
those with the most vertical development.
Thunderstorms have been known
to produce extreme turbulence as far as
20 nautical miles from the parent storm.
Request a wide deviation from air traffic
control to give yourself and your passengers
some added protection. A good rule
of thumb is to avoid flying through
any build-ups with a cloud depth higher
than 10,000 feet.
A variety of resources are available
for flight planning to help you avoid the
bumps. The turbulence imagery available
on your favorite electronic flight
bags originate from NOAA's Aviation
Weather Center in Kansas City. Those
graphical products center around something
called the Eddy Dissipation Rate
(EDR). This rate is derived from model
data and essentially shows how much
the air is mixing. The more mixing in the
atmosphere the bumpier the ride. On the
aviationweather.gov website, the turbulence
product is user configurable with a
sliding altitude scale as well as a forecast
time extending to 18 hours.
Keep in mind that what is severe
turbulence for one aircraft may not be
the same for another. Light to moderate
turbulence for a Boeing 767 could be
severe turbulence for a Piper Cherokee.
Fortunately, the legend for these products
reflects light, medium, and heavy categories
of aircraft. It is also important to note
with pilot reports, or pireps, what type
aircraft reported the turbulence.
While turbulence will always be
part of aviation, there are ways we pilots
can minimize the worst of it through
improved flight planning and watching
for visual cues once in the air. In
the meantime, I will keep analyzing the
data to give my wife a more comfortable
flight. JP Dice is a veteran meteorologist,
flight instructor, and corporate pilot flying
Cessna Citations and Gulfstreams.
Partner-provided content
Finding a smooth flight for
your passengers
Fronts, airmets, sigmets,
turbulence, and pireps can help a
pilot get the big picture and find
smooth air. Watch how corporate
pilot Justin Siems uses all these
SiriusXM features during the
preflight and en route to keep
his passengers comfortable at
SiriusXM.com/Justin.
AOPA PILOT / July 2024
87
http://www.aviationweather.gov http://www.SiriusXM.com/Justin
AOPA Pilot Magazine - July 2024

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