How Do Pilots Deal With Thunderstorms?

Jul 8, 2019

This post contains references to products from one or more of our advertisers. We may receive compensation when you click on links to those products. Terms apply to the offers listed on this page. For an explanation of our Advertising Policy, visit this page.

Late spring and summer bring hot weather and with it, thunderstorm season in the US. If you’ve been delayed in your travels in the past month or so, you already know that. With some 40,000 thunderstorms annually around the world, pilots are dodging them daily. Here’s how they assess thunderstorm threats and adjust their flight plans accordingly.

Pilots call thunderstorms “CB,” which refers to cumulonimbus clouds.

According to the FAA’s weather guide for pilots, a thunderstorm is not an object, but more akin to a process that develops within cumulonimbus clouds. Those clouds start as the friendly, puffy white clouds you see on sunny summer days — cumulus clouds — with the addition of fast-rising moisture that turns into rain. (Cumulonimbus means heaping rain in Latin—a heaping rain cloud. Not so friendly.)

Thunderstorm development, from building stage to maturity and dissipation. (Image via FAA Weather Guide.)


Chris Brady, a longtime Boeing 737 and Airbus A320 pilot in Europe who runs the Boeing 737 Technical Site and Facebook Page, has seen his fair share of thunderstorms aloft — from a safe distance, of course.

“The moisture comes from the oceans or the land after rain,” he said. “You won’t be able to see the moisture at ground level, but as the day heats up and the air starts to rise, the moisture eventually condenses out, forming a cloud.”

In simple terms, thunderstorms occur when rising, humid air quickly and violently builds high into the sky. The air eventually cools to a point where the moisture condenses into rain. “Creating rain” releases heat, which makes the cloud grow even higher. Meanwhile, the falling rain leads to lightning and brings with it fast-moving, downward air as the rain falls. In a thunderstorm, there’s air moving upward and sideways very quickly — some 3,000 feet per minute — even as air is also being pulled down by the rain itself. It’s a nasty cycle. And that’s just a single thunderstorm cell; there can be multiple cells across long weather fronts stretching hundreds of miles.

Thunderstorms can be huge, from 30,000 feet to 60,000 feet high and as wide as 100 miles across. An airplane can’t fly over them—their service ceilings won’t allow for it. The FAA guidance is to avoid thunderstorms by at least 20 nautical miles, or 23 statute miles. And for good reason. Inside, the winds go in all directions, often violently. Plus, there’s a good chance of hail.

“Believe me when I say that a long detour is worth it. No pilot would ever knowingly go into a thunderstorm,” says Brady.

For example, see what the pilots of Delta Airlines flight 1886 did on July 7 on their route from Atlanta to New York: they held in a racetrack pattern over Virginia to wait for the storms over New York to clear, and then reached LaGuardia Airport with a long detour over Pennsylvania. That route took almost an hour longer than normal, but avoided flying the Airbus A321 through a violent summer storm.

Screenshot from
Screenshot from


The issue with thunderstorms is not the lightning, except when that lightning is near the airport, causing a stop to ground operations. “Aircraft are designed to be able to withstand lightning strikes and every airliner gets struck, on average, six times a year,” Brady says.

“The fuselage acts like a Faraday cage, transmitting the lightning safely around the aircraft rather than through it, and generally, no damage is done.”

Preflight Preparation by Pilots

The incredible scale of convective activity. This image was shot by Chris Brady en route, capturing an aircraft safely skirting a thunderstorm cell.

“Most airlines don’t give their crew any advance warning of bad weather before they get to the airport. We as pilots just keep an eye on the regular TV or radio weather forecasts for that,” Brady said.

“When we report to the crew room before a flight we are given as much meteorological data as we need. This includes weather reports, forecasts, warnings, charts and satellite imagery,” Brady said. “From this data we will make a decision about the route we will fly and how much extra fuel we need to carry, both to pick our way around the storms and if necessary to hold or divert at the intended destination.”

What happens if thunderstorms are predicted on arrival at LAX for a flight departing New York? Does the aircraft still depart New York for Los Angeles?

“It depends upon each airline what their policy would be, but most would allow the flight to set off. The forecast is only a forecast and they can be wrong,” Brady said. “However, good practice would dictate, if there were CBs forecast at the destination, that you review the weather forecasts at the other airports nearby so that you have enough fuel to get to an airport which is not forecasting thunderstorms, in case yours is closed. Flying faster is an option but realistically we can only increase speed by a few percent so it doesn’t make that much of a difference.”

En-Route Technology

Brady explained that modern commercial aircraft have weather radar which superimposes weather information onto the map display for the pilots. The information comes from a radar antenna in the nose of the aircraft. The radar works by detecting water particles and displays different colors depending upon the density of water.

Chris Brady's A320 in the center, with CB cells in red, and if you look closely, lightning and turbulence. Image via Chris Brady.
On this flight-deck display, Chris Brady’s Airbus A320 is a yellow cross in the center. CB cells are in red, and if you look closely, you’ll see lightning (zigzags) and hail (yellow triangles). Anything that is striped is below the aircraft, and solid colors are above the aircraft. (Image by Chris Brady.)


“Green is the lowest level and is OK to fly into. Amber is quite strong and should be avoided if possible. Red is the center of the [thunderstorm] and absolutely must be avoided,” Brady says.

Brady explained there are other elements on the screen that show turbulence, and newer displays show lightning and hail, as seen above. Brady recently navigated through a series of CBs, shown on the images below.

“We picked our way through, taking care to allow for the way the storms were moving by looking at the wind speed and direction shown in the top left corner of the screen. If you look at the left screen (the primary flight display) you can see that we were at 37,000ft and the tops of the CBs were still well above us,” he said.

Navigating CB activity. (Image by Chris Brady.)


“It was slightly turbulent, and in these conditions the speed increases and decreases in the moving air,” Brady explained. In the case above, the flight instruments showed that at the plane’s very high 37,000-foot altitude, there was a very thin margin, only 40 knots or 46 mph, between the stall speed — when the aircraft would be too slow to fly — and overspeed, which stresses the plane’s structure. So, trying to avoid those CB clouds by sipmly going above them would have been hazardous indeed.

“This is why you should never try to overfly a storm,” Brady said. “The speed variations can be considerable, and you could inadvertently stall into a storm.”

Mike Arnot is the founder of Boarding Pass NYC, a New York-based travel brand, and a private pilot.

Featured image by Getty Images

Delta SkyMiles® Platinum American Express Card

Earn 90,000 bonus miles after you spend $3,000 in purchases on your new Card in your first 3 months. Offer ends 8/3/2022.

With Status Boost™, earn 10,000 Medallion Qualification Miles (MQMs) after you spend $25,000 in purchases on your Card in a calendar year, up to two times per year getting you closer to Medallion Status. Earn 3X Miles on Delta purchases and purchases made directly with hotels, 2X Miles at restaurants and at U.S. supermarkets and earn 1X Mile on all other eligible purchases. Terms Apply.

Apply Now
More Things to Know
  • Limited Time Offer: Earn 90,000 bonus miles after you spend $3,000 in purchases on your new Card in your first 3 months. Offer ends 8/3/2022.
  • Earn up to 20,000 Medallion® Qualification Miles (MQMs) with Status Boost® per year. After you spend $25,000 in purchases on your Card in a calendar year, you can earn 10,000 MQMs up to two times per year, getting you closer to Medallion® Status. MQMs are used to determine Medallion® Status and are different than miles you earn toward flights.
  • Earn 3X Miles on Delta purchases and purchases made directly with hotels.
  • Earn 2X Miles at restaurants worldwide including takeout and delivery in the U.S., and at U.S. supermarkets.
  • Earn 1X Miles on all other eligible purchases.
  • Receive a Domestic Main Cabin round-trip companion certificate each year upon renewal of your Card. Payment of the government imposed taxes and fees of no more than $80 for roundtrip domestic flights (for itineraries with up to four flight segments) is required. Baggage charges and other restrictions apply. See terms and conditions for details.
  • Enjoy your first checked bag free on Delta flights.
  • Fee Credit for Global Entry or TSA PreCheck® after you apply through any Authorized Enrollment Provider. If approved for Global Entry, at no additional charge, you will receive access to TSA PreCheck.
  • Enjoy an exclusive rate of $39 per person per visit to enter the Delta Sky Club® for you and up to two guests when traveling on a Delta flight.
  • No Foreign Transaction Fees.
  • $250 Annual Fee.
  • Terms Apply.
  • See Rates & Fees
Regular APR
17.24%-26.24% Variable
Annual Fee
Balance Transfer Fee
Recommended Credit
Terms and restrictions apply. See rates & fees.

Editorial Disclaimer: Opinions expressed here are the author’s alone, not those of any bank, credit card issuer, airlines or hotel chain, and have not been reviewed, approved or otherwise endorsed by any of these entities.

Disclaimer: The responses below are not provided or commissioned by the bank advertiser. Responses have not been reviewed, approved or otherwise endorsed by the bank advertiser. It is not the bank advertiser’s responsibility to ensure all posts and/or questions are answered.