Bumps in the Blue

This piece originally ran in Robert’s Stick and Rudder column in the September 2023 issue of EAA Sport Aviation magazine.

None of us like a rough ride in an airplane, but it seems that the skies are perhaps becoming more turbulent than in the past. Lately we’ve been hearing more from meteorology and climatology experts about how our global environment is changing.

Regardless of the cause, evidence suggests that our planet is warming. With that comes changes to the flight environment: stronger storm systems and extreme weather conditions that last for extended periods.

No matter where or what we fly, we can expect to encounter a few bumps in the blue that might remind us to slow to maneuvering speed. Some conditions are rife for a rough ride, and these deserve additional precautions.

Jockeying the Jet Stream

One likely place to encounter tooth-rattling turbulence is near the edges of the jet stream. The jet stream, as we know, is a fast-moving current of air high in the troposphere that circles the mid-latitudes in both the northern and southern hemispheres. It meanders north and south as it flows and brings with it a steady stream of weather systems.

As small airplane pilots, we don’t have to worry too much about jet stream turbulence, but that doesn’t mean we won’t be affected by changes in the jet stream. Studies now indicate a possible northward shift of the jet stream, which results in a more rapid warming of surface temperatures in North America, resulting in more severe extreme weather events. With that comes more turbulence.

Thunderstorms

While most of us don’t have to worry as much about tangling with the jet stream, we do need to step carefully when dancing about in thunderstorm territory. Thunderstorms inherently produce highly turbulent conditions that can cause aircraft structural damage or failure.

Pilots should stay at least 20 miles away from severe thunderstorms and their overhanging anvils. In addition to the wind shear, thunderstorms can spawn tornadoes and can produce extremely dangerous hail — even throwing it out into clear air ahead of the cell.

Regardless of size or appearance, never attempt to fly beneath a thunderstorm. Turbulence and wind shear beneath the storm can be a killer. Likewise, we should never venture beneath a thunderstorm’s anvil, as it often contains extreme clear air turbulence.

Never attempt to take off or land in the face of a hurricane. The updrafts, downdrafts, gusts, and turbulence can easily result in a loss of control. Likewise, avoid flying into an area where embedded thunderstorms may be present. Never assume ATC can provide vectors around embedded thunderstorms. They typically cannot.

The data-linked weather radar we use while flying is often 15 to 20 minutes old or more, so while it might warn us of approaching storms, it is extremely misleading when attempting to navigate around cells. We should completely avoid areas where thunderstorm coverage is six-tenths or more.

Wake Turbulence

Another form of turbulence to avoid is wake turbulence — the horizontal tornadoes formed as higher-pressure air beneath a wing slips around the wingtip to the lower pressure area above the wing. Not only is the resulting turbulence a problem, but the rotational effect can far exceed our aileron control.

Remember that these wakes are more pronounced when an aircraft is heavy, slow, and dirty (flaps and gear down), and the wakes slowly drift below and outward from the flight path of the aircraft.

The Pilot’s Handbook of Aeronautical Knowledge provides several tips to minimize the chances of flying through an aircraft’s wake turbulence.

On departure, we should rotate prior to the point at which a preceding aircraft rotated. If a large aircraft departs ahead of us, we should wait three minutes before our own departure. Remember that a gentle crosswind can cause the vortex to remain on the runway for longer periods. In flight, we should avoid flying through another aircraft’s flight path, and avoid following another aircraft at an altitude within 1,000 feet below that aircraft.

When landing, we should approach the runway above a preceding aircraft’s path and touch down after the point at which the other aircraft’s wheels contacted the runway.

While we typically think of wake turbulence in regard to large commercial airliners, even smaller aircraft can produce dangerous wake turbulence. Helicopters also produce vortices when airborne, as well as dangerous turbulence from their downwash when hovering. The rule is to avoid hovering helicopters by a distance of at least three rotor lengths.

Mountain Wave Turbulence

A common phenomenon in mountainous terrain is what is referred to as mountain wave turbulence. It typically occurs when mountaintop winds exceed 25 to 30 knots, the wind is nearly perpendicular to the mountain range, and unstable air at the surface is capped by a layer of stable air above.

Such a condition can set up an oscillating flow of air — waves that can extend a hundred miles or more downwind from the mountain range. While sometimes rotating “rotor clouds” may be visible beneath the wave crests, the dangerous turbulence is often invisible.

To avoid the turbulence, avoid areas where mountain wave activity may exist. When flying parallel to a mountain range, adjusting our distance from the range by a few miles or more might put us in smoother conditions. Extreme caution is needed when traversing high terrain since severe downdrafts and turbulence are often encountered on the downwind side of mountain ridges.

Remember, you don’t need “mountains” to create mountain waves and turbulence. Any terrain features that protrude into a current of wind can cause turbulence, updrafts, and downdrafts. Cities with tall buildings create hazardous wave activity. Even a structure near a runway or uneven or sloping terrain can cause troublesome turbulence when the wind is blowing.

Hurricanes on the Horizon

One factor we may not have considered is how changes in weather patterns can alter our expectations for hurricane season. Experts tell us that years in which La Niña conditions persist, we typically experience more and perhaps more powerful hurricanes in the Atlantic Ocean than those years in which El Niño conditions persist.

El Niño refers to a condition of above average temperature ocean surface waters in the central and eastern tropical Pacific Ocean. This condition alternates with La Niña — a cooler than average ocean surface temperature in the same region. These conditions have a strong influence on the global climate, including changes in rainfall and low-level trade wind patterns, which in turn influence hurricane development in the Atlantic. El Niños occur at irregular intervals of two to seven years and typically last from nine months to two years.

We don’t need reminders to avoid hurricanes, but turbulence isn’t our only concern. In the wake of a hurricane, expect flooding and damage to infrastructure that can undermine our plans. Runways, lighting systems, automated weather systems, fueling facilities, and maintenance facilities can all be out of service for an extended time following severe storms and hurricanes. We need to perform our due diligence to ensure the required infrastructure is intact. Beyond what is included in NOTAMs, consider what might not be available, including ground transportation, services, hotels, even food and water.

We all want to avoid those uncomfortable bumps in the blue. By taking the right precautions, we can minimize the rough ride created by turbulence.

Robert N. Rossier, EAA 472091, has been flying for more than 40 years and has worked as a flight instructor, commercial pilot, chief pilot, and FAA flight check airman.