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Capabilities and limitations of ATC weather information

Even more than VFR flying, where the goal is to avoid all bad weather, instrument flying requires an in-depth knowledge of weather theory and patterns in order to see and interpret what’s happening while flying in marginal conditions.
Illustration by Leigh Caulfield
Illustration by Leigh Caulfield

What’s more, good instrument pilots not only know how to gather this information, but how to act on it.

You’re no doubt familiar with what flight service can offer in terms of weather insights in flight and on the ground, and other useful places to head to for various weather products during the planning phase. But those are only some of the services available to you. Properly utilizing air traffic control is a skill that’s often overlooked.

Helping pilots with weather advisories is a key requirement for controllers, and without question they want to see you arrive safely. So, when the information is available, they will readily offer it. But that information may not be as detailed as you would imagine.

Hazardous in-flight weather advisories are the most broad and top-level alerts from controllers. When issued, the controller must broadcast the alert to all the aircraft on the frequency as quickly as possible. These broadcasts are sort of like if Google Maps told you about an accident that occurred in the same county. It’s general information that may have no impact on your trip, or it might be a major thunderstorm right in the middle of your route. Knowing which is up to you, but if you’ve kept abreast with the weather, or you got a detailed briefing, hearing the alert probably won’t be a surprise.

The pilot is in charge of the flight. If you need to know something, you need to ask.
Thankfully the resources from ATC don’t end there. Depending on whether you’re working with a tower, approach, or center facility, the information available to controllers can vary from detailed National Weather Service radar imagery to something that would have been at home on your 1980s Atari. Most facilities have high-resolution National Weather Service radar in the building, but not necessarily on the controller’s scope. The controller probably has a good idea of what’s happening out there, but he or she may not be able to directly correlate that detailed picture to your flight. However, approach and center both have radar that displays precipitation in different strengths. Approach radar may give the controller precipitation in four strengths, no intensity, or two intensities. Center’s radar is more homogeneous, and advisories are issued for three levels. Thus, some approach controllers can tell you if the precip is light, moderate, heavy, or extreme; some can tell you moderate or heavy/extreme; and some will say intensity unknown. Center controllers will only be able to tell you if the precip is moderate, heavy, or extreme (their systems filter out light precip to reduce clutter). Suffice to say, the information is limited.

What’s more, it’s only precipitation. The controllers don’t know if it’s snow, rain, sleet, freezing rain, or hail. And they don’t know if it’s related to convective activity, whether it’s hitting the ground, or how long it might last. Those are all things for you to decide. What they do know is generally where it is, the intensity, and the movement. Despite some of the limitations, many pilots find the precip information coming from center controllers to be superior to the composite images on their iPad or cockpit displays.

Remember that a controller’s primary responsibility is keeping airplanes from hitting each other. It’s why you can’t completely rely on ATC to tell you about the weather they may see on their displays. Issuing a weather alert, while important, simply isn’t a controller’s primary task. And when the weather is lousy, pilots have more needs, which keeps the controllers busy. Things can snowball enough to the point that they don’t have time to pre-emptively tell you about the weather. And that’s the most important takeaway.

The pilot is in charge of the flight. If you need to know something, you need to ask. The cloud ahead look a little mean? Ask the controller if he or she sees any precip, what previous aircraft have reported, and even for a suggested reroute. Feel like things are closing in on you? Ask if they see a hole and for a vector.

As part of your weather training, listen to live air traffic on a day with poor weather. Airline pilots are experts at getting what they need from air traffic control, especially during poor weather. You’ll hear them ask questions, work together on reroutes, and seek clarification. This is what every pilot should aim to do. Get as complete a picture as possible and then ask for exactly what you want. Minor deviations left and right are almost always approved. Larger reroutes can often be accommodated, but try not to wait for the last minute to ask. Think ahead and figure out the route before you need it.

Many experienced instrument pilots make it a goal to completely avoid the weather. They see the airplane staying dry as a much bigger badge of honor than threading a tight gap between two storms.

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Ian J. Twombly

Ian J. Twombly

Ian J. Twombly is senior content producer for AOPA Media.

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