From thunderstorms and limited visibility to scorching temperatures and turbulence, the weather dictates when and where planes can fly. Severe weather is the leading cause of air travel disruptions in the United States.

Aviation meteorologists plan for and around difficult conditions, crafting weather forecasts used to determine the nuances of flights, from altitude to optimal routes. They play an essential role in ensuring travelers get to their destinations safely and efficiently.

Several major domestic carriers, including Delta Air Lines, have in-house meteorologists who monitor global weather 24 hours a day. Delta has 28 meteorologists on staff — the largest team of any airline, it declares — who sit in the carrier’s Operations and Customer Center, alongside flight dispatchers, customer service agents and hundreds of other staffers, at its headquarters in Atlanta.

In this cavernous and screen-filled room, Warren Weston, Delta’s lead meteorologist, recently spoke about the importance of data, the difference between surface weather and upper-air hazards, and how even one degree of temperature can change a flight plan. The conversation has been edited and condensed for clarity.

What are your team’s main responsibilities?

The team provides weather briefings covering Delta’s global operations four times a day.

We write our own forecasts for the 10 main Delta hubs in the United States. One of the things that makes us unique is that we are the sole weather provider for Delta. Sometimes our timing will differ from that of the National Weather Service; we might be calling for a slower changeover from snow to rain, for example. The Weather Service doesn’t have to see the people they write these forecasts for, but we have the flight dispatchers right here.

It’s a 30-hour forecast updated every six hours. I guess the moral of the story is data, data, data. We rely on government and university models, and then proprietary in-house tools.

What kind of weather conditions are analyzed?

This is completely different than the forecast that you would see on your smartphone app. It is a special aviation forecast giving the dispatchers and the pilots information about variables like wind speed and direction.

We are in two modes here: surface weather and upper air. Surface conditions are visibility, precipitation and clouds. On the upper-air side, we are mostly watching for turbulence, the primary threat. We’re also looking for volcanic ash (a rock mixture debris released when a volcano erupts), thunderstorms and tropical storms. Occasionally we have ozone issues.

So flight planning begins with the weather. How are forecasts used?

Our goal is to give enough lead time so dispatchers and other decision makers can make proactive operational decisions, rather than waiting for something to happen.

On our screens, we can see every Delta flight that’s in the air. I can see their route, where they’re going and exactly which dispatcher is in charge of that flight if we needed to communicate with them.

We update the forecasts hours before flights take off. If anything changes, all we have to do is walk over to the dispatchers to suggest areas to avoid or a different altitude.

We always monitor weather for active flights in the air and adjust our hazard alerts for conditions like turbulence, thunderstorms and volcanic eruptions, based on new data. Dispatchers and pilots can easily reach us mid-flight and we can discuss any weather concerns.

What do you do when bad weather is in the forecast?

Say Thursday looks like it’s going to be extra active with thunderstorms over the Northeast. At that point, flight dispatchers and customer service agents can start working on a plan, both for the customers and from an operational perspective — considering whether they need to send out alerts to the customers because of severe weather, about thinning the flight schedule to lessen delays. They’ll allow customers more flexibility to change flights.

The Federal Aviation Administration regulations require us to have an alternate airport in case of emergencies like mechanical problems or customer medical crises. So we also write special forecasts for these alternate areas.

What are the most common types of severe weather causing flight delays or cancellations?

It definitely depends on the region, station and season. Atlanta, New York, Florida and the East Coast are prone to severe thunderstorms in the summer that cause disruptions. Similarly, we see winter weather delays and cancellations in places like Detroit, Minneapolis and Salt Lake due to de-icing and ramp/runway conditions.

If you’ve got a thunderstorm over the airport, that will prevent you from landing. That’s probably the main one; another could be thunderstorms en route. That could cause planes to fly a different and longer route.

Then in winter, with freezing precipitation you have to worry about de-icing the airplane and general airport conditions, like whether the snow plows will be able to keep up with the snowfall. This is outside of Delta’s control; you’re acting on something that’s being handled by the airport authority.

There’s so many things that can cause delays, and they all vary based on airline, and they all vary based on city. If we had an inch of snow here in Atlanta, obviously everything comes to a grinding halt. We’re just not equipped to handle that type of stuff.

This summer has seen record temperatures. What happens to planes during extreme heat?

When it’s really hot, the planes can carry a little bit less weight than they normally would, so that means fewer passengers and less baggage. There are also ramp workers to consider.

Even one degree makes a difference. We know what the problem-points are for all our airports — whether it’s temperatures, thunderstorms or snow on the runway — and for Las Vegas, if it’s hotter than 100 degrees Fahrenheit, every degree over 100 is going to mean about 1,400 pounds off.

What should passengers know about weather and air travel?

Bad weather at another airport can still cause delays for your flight, even if the weather is perfect where you are. Those delays can cascade and cause effects in places where the weather is great.

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