Published: November 23,2016
Flight delays due to weather are an unfortunate reality, especially at some of the busiest airport hubs in the United States.
Roughly one-third of all arrivals from October 2015 through September 2016, the latest 12-month data period available as of this column, were delayed at least 15 minutes by weather, according to the U.S. Department of Transporation's Bureau of Transportation Statistics.
This amounted to 312,595 weather-delayed arrivals, totaling about 20.2 million minutes. Putting all those minutes together is the equivalent of just over 38 years of weather delays.
Heavy snow blankets Buffalo-Niagara International Airport, New York, on January 13, 2016. (BUFAirport/Twitter)
A study by the University of California-Berkeley estimated the following staggering costs of flight delays in 2007:
• $32.9 billion total cost to U.S. economy – more costly than all U.S. hurricanes except Katrina and Superstorm Sandy.
• Of that total, $16.7 billion was borne by passengers in lost time and additional travel expenses.
• Gross domestic product was reduced by $4 billion.
In addition, a 2007 congressional study estimated 740 million gallons of additional jet fuel was burned due to flight delays, about five percent of total fuel consumption.
For our list of the most weather-delayed major airports, we considered the raw number of weather delays as well as the percentage of all delay minutes due to weather at the 29 major U.S. airports.
We ranked each airport in each of those two categories, then added the rankings together to come up with our composite index. The lower the index, the more weather-delayed that major hub was from October 2015 through September 2016.
10. Philadelphia International Airport (PHL)
(Getty Images)
| On-time Percentage | 79.82 percent |
| Weather Delays / Ranking | 5,777 / 15th worst |
| Percent of Delay Minutes Due to Weather / Ranking | 44.33 percent / 7th worst |
| Composite Index | 22 |
| Weather Issues | Low clouds/fog, wind, snow, thunderstorms |
Overall, about 20 percent of all arrivals into Philadelphia are delayed. In some ways, they're a victim of close proximity to other major Northeast airports, and the propensity for delays to ripple through the network.
Philly sits in the middle of the pack in most of our weather criteria. For instance, they average only about 23 inches of snow a year, with measurable snow 12 to 13 days annually. Philadelphia is not especially windy, and its 27 days a year with thunderstorms is, again, not too noteworthy.
9. Dallas-Ft. Worth International Airport (DFW)
(Caren Mack Photography/Flickr)
| On-time Percentage | 80.35 percent |
| Weather Delays / Ranking | 13,427 / 5th worst |
| Percent of Delay Minutes Due to Weather / Ranking | 34.25 percent / 13th worst |
| Composite Index | 18 |
| Weather Issues | Thunderstorms, fog, rare snow/ice |
A severe weather outbreak in North Texas on April 3, 2012, triggered 800 flight cancellations and 550 delays at DFW. More than 100 aircraft were damaged by baseball-sized hail. Some 1,400 people had to spend the night in the airport’s terminals.
But it doesn’t take tornadoes and huge hail to mess up flight plans in this hub. Slow-moving thunderstorms with heavy rain in the summer months can also push back flight schedules. On average, thunderstorms hit the Metroplex 47 days each year.
Snow, sleet or freezing rain is rare, but it can have major effects on DFW.
Two rounds of snow blanketed the area in February 2011. The airport was closed for several hours during the first round on Feb. 2, and the second round dumped 6 inches of snow on the metro area. With annual snowfalls reaching only 1 to 2 inches on average, travelers should expect flight delays at this airport any time snow or ice is present in North Texas.
8. Boston Logan International Airport (BOS)
(Daniel Schwen/Wikimedia)
| On-time Percentage | 78.6 percent |
| Weather Delays / Ranking | 10,323 / 9th worst |
| Percent of Delay Minutes Due to Weather / Ranking | 43.13 percent / 8th worst |
| Composite Index | 17 |
| Weather Issues | Snowstorms, fog |
According to Massport, the organization responsible for the condition of the airfield, most weather events don’t shut down the airport. Lengthy delays can happen, not just because of snow removal, but from delays from other Northeast hubs.
"If New York sneezes, Boston catches a cold," said Matthew Brelis, director of media relations at Massport. Since most Boston-bound domestic flights pass through New York’s airspace first – even flights coming from cities like Phoenix or Seattle – any inclement weather in the Big Apple can delay flights in Boston.
Aside from winter weather, fog and rain can also factor into flight delays in Boston, Brelis said. Additionally, Boston Logan is the windiest major airport in the country. A typical Northeast cold front can produce wind gusts as high as 30 to 40 mph.
Boston also lands near the top of the major hubs for average snow (43.5 inches) and days with measurable precipitation (126 days a year). Even the most prepared airport would have plenty of weather-related days with that much chaos swirling around it.
7. John F. Kennedy International Airport (JFK)
(Chris Hondros/Getty Images)
| On-time Percentage | 76.47 percent |
| Weather Delays / Ranking | 9,570 / 10th worst |
| Percent of Delay Minutes Due to Weather / Ranking | 48.46 percent / 6th worst |
| Composite Index | 16 |
| Weather Issues | Snowstorms, low clouds/fog, wind, thunderstorms |
New York City ranks just above the middle of the pack for both average snowfall (23 inches per snow season) and days with measurable snow in a year (14 days).
Despite that, snowstorms can cripple air travel for a full day or longer at this airport, as well as the major airports nearby.
Snowstorms aren’t the only factors that trigger delays. Frontal systems can also cause delays when they’re accompanied by low clouds.
Of the New York area’s three major airports, JFK saw the fewest arrivals in the time period we studied, but there were more than enough delays to vault this hub into our top 10.
6. George Bush Intercontinental/Houston Airport (IAH)
(Stan Honda/AFP/Getty Images)
| On-time Percentage | 82.66 percent |
| Weather Delays / Ranking | 10,389 / 8th worst |
| Percent of Delay Minutes Due to Weather / Ranking | 48.54 percent / 5th worst |
| Composite Index | 13 |
| Weather Issues | Thunderstorms, fog |
First, thunderstorms frequent the metro area 62 days during an average year, and those storms can happen year-round, even while the rest of the nation is shivering in the middle of winter.
While these thunderstorms can be severe, the key for airport delays, most of the time, is that these storms can move slowly. Instead of a 30- to 60-minute delay, flights can be pushed back far more than an hour if a cluster of thunderstorms takes its time.
Then, there’s fog and low clouds. Because of the city’s proximity to the Gulf of Mexico – as well as Galveston Bay, the Houston Ship Channel and numerous bayous – Houston is prone to fog. Dense fog is seen roughly 18 days a year, while patchier fog is observed 70 days annually.
It’s also worth mentioning that Houston is at risk for tropical storms and hurricanes, primarily from June through September, but that didn’t factor into the data we studied for this list.
5. Denver International Airport (DEN)
(Chin Tin Tin/Wikipedia/Creative Commons)
| On-time Percentage | 82.39 percent |
| Weather Delays / Ranking | 15,186 / 3rd worst |
| Percent of Delay Minutes Due to Weather / Ranking | 40.93 percent / 9th worst |
| Composite Index | 12 |
| Weather Issues | Snowstorms, thunderstorms, hail, tornadoes |
Formally opened in 1995, Denver International Airport's main weather challenge is snow. Colorado Front Range snowstorms are legendary, occurring as early as October and as late as April.
In late spring and summer, afternoon and evening thunderstorms can be almost a daily ritual. This is due to heating of the mountains west of the city, allowing somewhat moist winds to converge and rise near the peaks, building thunderstorms which then drift onto the adjacent Front Range urban corridor.
If that's not enough, under the right conditions, the Denver Convergence Vorticity Zone (DCVZ) or Denver cyclone can form near the airport. This is a boundary of converging air that can serve as another focus for thunderstorm development, some of which can spin up tornadoes. Tornado sightings from the tower at DIA are not uncommon in late spring and early summer.
Given the propensity for thunderstorms, and the high elevation, it should come as no surprise that the Front Range is a notorious corridor for large hail, as well. In July 2011, a hailstorm damaged numerous planes at DIA, triggering flight cancelations for days after. This is not something you'd typically expect to delay your flight.
On a personal level, my first weather encounter with DIA was not snow, or thunderstorms, but turbulence. In fact, it was my first trip on a plane. Returning to Colorado from a visit home for the holidays, we were on our descent into DIA when it began to feel like God was shaking the plane like a pepper shaker. Alright, slight exaggeration: it wasn't severe turbulence. Thankfully, nobody was injured. But this first-time flyer was rattled.
4. New York LaGuardia Airport (LGA)
(Don Emmert/AFP/Getty Images)
| On-time Percentage | 72.66 percent |
| Weather Delays / Ranking | 12,026 / 7th worst |
| Percent of Delay Minutes Due to Weather / Ranking | 52.95 percent / 3rd worst |
| Composite Index | 10 |
| Weather Issues | Snow, low clouds/fog, wind, thunderstorms |
Snowstorms are the most frequent instigators of massive flight delays and cancelations at the metro's big three airports, but aren't the only weather nuisance.
Situated on Flushing Bay, storm surge from Superstorm Sandy flooded LaGuardia's runways on Oct. 29, 2012, pushing as far as the terminal buildings and jetways.
Fortunately, many planes were moved ahead of time to other airports as a precaution. Flights did not resume until two days later.
A line of thunderstorms ahead of an advancing cold front into the Northeast can also trigger significant flight delays on the order of several hours. Fortunately, thunderstorm days (24 to 26 each year, on average), aren't nearly as numerous as, say, Houston, Denver or Atlanta.
Of course, it's not just rain or snow that can delay your flight to the Big Apple. Low clouds and fog can trigger big delays. We'll talk more about wind delays at these airports when we arrive at another NYC metro airport in our top 10 list.
3. Chicago O'Hare International Airport (ORD)
(Scott Olson/Getty Images)
| On-time Percentage | 80.14 percent |
| Weather Delays / Ranking | 21,451 / 2nd worst |
| Percent of Delay Minutes Due to Weather / Ranking | 49.64 percent / 4th worst |
| Composite Index | 6 |
| Weather Issues | Snow, low clouds/fog, wind, thunderstorms |
Weather systems in the Midwest generally move from west to east, and at O’Hare, arrivals typically approach from the east. This makes flying around any adverse weather system a challenge.
Because Chicago averages more snowy days than any Northeast hub each year, wintry weather can also be a major hassle for O’Hare. The Windy City sees about 28 days of snow per year on average, and O’Hare tops all major Northeastern airports with about 38 days with thunderstorms a year.
And there’s the wind. South or southwest winds – usually the prevailing direction from June through November – can lead to delays, even on sunny days. Additionally, Chicago gets about 13 days a year of dense fog, which is possible year-round.
A poorly timed dense-fog event shrouded the airport the day before Thanksgiving in 2012. Traveler volume was extremely high. More than 100 flights were canceled and at least 300 more flights were delayed at O’Hare before the fog slowly dissipated.
The sheer number of weather-related delays reported by the U.S. DOT was what landed O’Hare so high on our list, but some of those arrival delays may have been because of bad weather at a flight’s airport of origin. Still, if an incoming flight is delayed at this airport, there’s nearly a 50 percent chance it’s because of weather.
2. Newark Liberty International Airport (EWR)
(Jeff Zelevansky/Getty Images)
| On-time Percentage | 75.5 percent |
| Weather Delays / Ranking | 13,731 / 4th worst |
| Percent of Delay Minutes Due to Weather / Ranking | 59.16 percent / 2nd worst |
| Composite Index | 6 |
| Weather Issues | Snow, low clouds/fog, wind, thunderstorms |
If your arrival to this hub was delayed in 2015 or 2016, there was an almost 6 in 10 chance it was due to weather.
Sure, snowstorms and the occasional summer thunderstorm can cause problems, but you might be surprised to learn it’s the wind that creates issues most frequently at this airport.
Two of Newark’s three runways are oriented southwest to northeast. Since west to northwest crosswinds are common, this is can be a frequent problem, even on sunny days. Winds can create headaches for pilots attempting to land, which is why you may see planes circling EWR on a picture-perfect afternoon.
1. San Francisco International Airport (SFO)
(Robert Alexander/Getty Images)
| On-time Percentage | 75.17 percent |
| Weather Delays / Ranking | 25,061 / Worst |
| Percent of Delay Minutes Due to Weather / Ranking | 63.29 percent / Worst |
| Composite Index | 2 |
| Weather Issues | Low clouds/fog |
The cause of this airport’s problems isn’t extreme weather – it’s fog and low clouds. When the marine layer is persistent, flight delays quickly add up.
In the warmer months, moist air from the cool Pacific Ocean is drawn into the Bay Area in the afternoon due to the pressure difference between the hot Central Valley and the chilly coast. This moist air then condenses overnight into low clouds, which hang in place until sunshine warms the layer enough to dissipate them.
During the winter months, fog can be more dense as cold air drains westward from the Central Valley and locks in.
There’s another problem that contributes to these weather delays: the layout of the airport’s runways, according to Nerd Wallet. Two sets of parallel runways make up SFO, and there’s only 750 feet between each runway. When visibility is low, the FAA doesn’t allow planes to land side-by-side unless runways are at least 4,300 feet apart, the report adds.
Arrivals must be staggered because of this conundrum, and the delays pile up.
Jonathan Erdman is a senior meteorologist at weather.com and has been an incurable weather geek since a tornado narrowly missed his childhood home in Wisconsin at age 7.
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