Hey everyone, welcome to another S.O.A.R article! In this week’s article, we will be looking at thunderstorms, the hazards associated with them, and how pilots can safely plan around and avoid convective weather while flying on VATSIM.

Thunderstorms are among the most hazardous weather conditions encountered in aviation.

A single thunderstorm can contain severe turbulence, wind shear, heavy precipitation, hail, icing, lightning, and powerful updrafts & downdrafts. These hazards can affect an aircraft well beyond what may be visible from the flight deck, meaning that simply remaining outside the cloud itself does not necessarily mean the aircraft is clear of the associated risks. Severe turbulence can extend as far as 20 NM from a severe thunderstorm.

Because of this, thunderstorm avoidance begins well before reaching the weather itself.

Pilots should identify areas of convective activity during flight planning and continue monitoring conditions with METARs, TAFs, SIGMETs, WXR (Weather Radar), etc. Weather several hundred miles ahead can also change significantly before the aircraft reaches it, so information checked before departure should also not be considered the final picture for any flight.

Weather avoidance also requires looking beyond the destination airport. A destination may be reporting perfectly acceptable conditions while a line of thunderstorms blocks the planned arrival route. Similarly, thunderstorms near an alternate airport may make that airport unsuitable by the time it is required. Pilots should therefore consider the entire route and have a good idea of what options are available if conditions deteriorate.

Understanding Weather Radar

Weather radar is one of the most useful tools for identifying convective activity, but understanding what it displays is equally important. Airborne and ground-based weather radar primarily detect precipitation rather than turbulence itself. Generally, areas containing large amounts of precipitation produce stronger radar returns and may be associated with more significant convective activity. However, the appearance of a thunderstorm should never be used on its own to determine whether it is safe to approach.

Datalink weather also has its limitations. Depending on the system being simulated, radar imagery displayed in the flight deck may not represent the exact position or intensity of weather at that moment. Displayed weather information can be significantly older than its indicated age, so datalink radar should be used for strategic avoidance, rather than turning your aircraft into an F/A-18 Hornet and trying to weave through individual storm cells.

In practical terms, weather radar should help answer: “Where should I avoid?” rather than “What is the smallest gap I can fit through?”

This becomes especially important when several cells are close together. A gap that appears clear on a weather display may contain turbulence or may close as the cells develop.

Instead of waiting until the aircraft is directly in front of said weather, an earlier and wider deviation typically gives both the pilot and ATC more options.

Thunderstorm Avoidance

The best way to deal with a thunderstorm is generally not to enter one in the first place. Thunderstorms identified as severe or producing intense radar returns should be avoided by at least 20 NM, including the anvil of a large cumulonimbus cloud.

This does not mean that 20 NM should be treated as a universal boundary where every thunderstorm suddenly becomes safe. The severity and development of the storm, surrounding cells, available weather info, and aircraft capabilities all need to be considered. Recommended or required avoidance distances may also differ between operators and their procedures. A line of closely spaced thunderstorms may require a much larger deviation or a completely different route rather than attempting to pass between individual cells.

Flying underneath a thunderstorm is also not a safe shortcut. Significant turbulence and outflow can exist below the cloud even when visibility beneath the cloud appears good. It’s cautioned not to fly underneath a thunderstorm, even when the end of the storm is visible.

Likewise, pilots should not assume that simply climbing above a thunderstorm will solve the problem. Thunderstorms can develop rapidly and reach very high altitudes. A developing cumulonimbus can also grow vertically extremely quickly, potentially faster than an aircraft can safely out-climb it. Vertical clearance guidance can vary between authorities and operators; for example, Transport Canada recommends clearing the top of a known or suspected severe thunderstorm by at least 1,000 ft for every 10 kt of wind speed at cloud-top level. Planning around the weather rather than trying to out-climb it will often provide the safer and more predictable option.

Working With ATC

Weather deviations are normal operations. However, responsibility for avoiding hazardous weather remains with the pilot. ATC may provide weather information or assist with a requested deviation when able, but pilots should not assume that a controller will automatically provide thunderstorm avoidance.

Pilots should communicate their intentions early rather than waiting until an immediate turn is required. Where possible, it is also useful to give ATC an idea of how large the deviation will be. This could include the direction of the deviation, an approximate distance off track, or how long the aircraft expects to remain on a requested heading.

On the network, a weather deviation might sound like:

1. Requesting a deviation:

• “Vancouver Centre, ACA123, request deviation 20 miles right of track due weather.”
• “ACA123, request heading 240 to avoid weather ahead.”

2. Unable to accept a clearance because of weather:

• “Unable direct DUXAR due weather, request present heading.”
• “Unable that routing due thunderstorms, request deviation right.”

3. Returning toward the planned route:

• “ACA123, clear of weather, able direct DUXAR.”
• “ACA123, clear of weather, able to resume own navigation.”

The exact wording does not need to be complicated. The important information is what the pilot needs to do and why. An early request also gives the controller more time to account for surrounding traffic and coordinate a different routing if required.

ATC may not always be able to accommodate a pilot’s preferred deviation due to surrounding traffic, airspace, or other operational constraints. Because of this, it is a good idea to have another suitable option available. This could mean deviating in another direction, accepting a larger reroute, holding away from the weather, or eventually diverting if necessary.

Pilots should ensure the route is clear of thunderstorms before accepting a clearance to rejoin it.

If the weather makes the original route impractical, pilots should also be prepared to accept a larger reroute or consider other options. A flight plan represents the intended route, but changing conditions may make following that route no longer practical.

Common Weather Avoidance Mistakes

One of the biggest mistakes is delaying a deviation in the hope that the weather will improve or that a small gap will remain open. Waiting until the aircraft is close to the weather reduces the amount of space available to manoeuvre and gives ATC less time to accommodate the request.

Another common mistake is relying too heavily on a single source of weather information. Radar imagery, METARs, TAFs, SIGMETs, visual observations, and other available information each provide different pieces of the overall weather picture. Using several sources helps pilots understand both the current conditions and how they may develop.

Pilots should also avoid following the original flight plan simply because it was filed before departure. If the planned route takes the aircraft toward hazardous weather, requesting a deviation, accepting a reroute, holding away from the weather, or diverting may all be better options.

Thunderstorm avoidance ultimately comes down to planning ahead, recognizing when conditions are becoming unsuitable, and making decisions early enough to keep your options open. Staying on the original route should never take priority over avoiding hazardous weather.

On VATSIM, this also means communicating with ATC early. Whether you need a small deviation, a significant reroute, or eventually a diversion, a clear request gives controllers more time to accommodate you and surrounding traffic.

A longer route around weather may add several minutes to your flight, but good airmanship is not about getting as close to a thunderstorm as possible. Plan ahead, give thunderstorms space, and communicate early.