Which US Airports Blame Weather Most? IAD Leads at 8.9%

Weather accounts for 6.1% of US flight delays nationally, but at Washington Dulles it runs 8.9% — the highest share of any major US airport.

Chicago O'Hare (8.5%) and Dallas Fort Worth (8.4%) aren't far behind. At the other extreme, Phoenix Sky Harbor logs weather-coded delays just 2.6% of the time — proof that a flight's real weather risk depends heavily on which airport it passes through, not just the season or the airline.

Here's what stands out across the 40 busiest US airports:

• Weather causes 6.1% of delay-minutes nationally — the second-smallest of the five DOT-tracked causes, behind only security (0.1%), across 14.1 million flights from June 2024 through May 2026.
• Washington Dulles (IAD) has the highest weather share of any major airport, at 8.9%, followed by Chicago O'Hare (8.5%) and Dallas Fort Worth (8.4%).
• Phoenix Sky Harbor has the lowest weather share, at 2.6%, with Las Vegas, Boston, and Portland tied at 2.8%.
• Indianapolis has the highest National Airspace System (NAS) share, at 28.8%, ahead of JFK (28.1%) and LaGuardia (27.6%) — congestion-heavy airports cluster at the top.
• Late-arriving aircraft cause half of all delay-minutes at Reagan National (50.1%), but only about a fifth at Delta's Minneapolis and Detroit hubs (19.8% and 19.1%).

The five official delay causes, and where weather ranks nationally

The US Department of Transportation requires every airline to sort each delay of 15 minutes or more into one of five categories: air carrier, weather, National Airspace System (NAS), security, or late-arriving aircraft. Weighted by delay-minutes across FlightRecord's full dataset — 14.1 million flights from June 2024 through May 2026 — the national split is late aircraft 39.3%, air carrier 34.0%, NAS 20.4%, weather 6.1%, and security 0.1%. Full definitions for each category are on our methodology page, and the national trend behind these five categories gets a closer look in our full breakdown of whether weather is really to blame for flight delays.

Which airports blame weather the most for delays?

Five major airports post a weather-coded share of delay-minutes above 8%, all comfortably ahead of the 6.1% national rate. Washington Dulles tops the list at 8.9%, with three more within half a point of each other close behind.

• Washington Dulles (IAD) — 8.9% of delay-minutes weather-coded, the highest of any major US airport; still posts an 83.2% on-time departure rate, above the 78.2% national average.
• Chicago O'Hare (ORD) — 8.5%; also the busiest airport in this comparison, with 355,671 departures in the past 12 months.
• Dallas Fort Worth (DFW) — 8.4%; American Airlines' largest hub, with a 72.3% on-time departure rate, below the national average.
• Minneapolis–Saint Paul (MSP) — 8.2%, tied with Charlotte.
• Charlotte Douglas (CLT) — 8.2%; American Airlines' busiest connecting hub in this comparison.

A high weather share and a poor on-time rate aren't the same thing. IAD's overall on-time rate beats the national average despite carrying the heaviest weather load of any major airport, while DFW combines a heavy weather load with a below-average on-time rate. The delay-cause split explains why a flight ran late, not how often it happens — see our methodology for how on-time rate itself is defined.

Which airports have the fewest weather-coded delays?

At the opposite end, six major airports keep their weather share under 3% of delay-minutes — mostly warm, dry, or Pacific climates with less exposure to severe convective storms and winter systems.

• Phoenix Sky Harbor (PHX) — 2.6%, the lowest of any major airport measured.
• Harry Reid International (LAS) — 2.8%.
• Boston Logan (BOS) — 2.8%.
• Portland International (PDX) — 2.8%.
• Honolulu (HNL) — 2.9%.
• Los Angeles International (LAX) — 2.9%.

Boston Logan is the exception on this list — a Northeast airport that keeps its weather-coded share as low as several desert airports, even though it ranks among the highest for NAS delays, described below.

What is a NAS delay, and which airports have the most?

A National Airspace System (NAS) delay covers non-extreme-weather, air-traffic-control-driven slowdowns: volume-based ground stops, gate holds, equipment outages, and staffing gaps that ripple through the network, sometimes originating hundreds of miles from the affected flight's own airport. Nationally, NAS accounts for 20.4% of delay-minutes, the third-largest of the five causes — and it's concentrated at a specific kind of airport.

• Indianapolis (IND) — 28.8%, the highest NAS share of any major airport measured.
• John F. Kennedy (JFK) — 28.1%.
• LaGuardia (LGA) — 27.6%.
• Boston Logan (BOS) — 27.1%.
• Newark Liberty (EWR) — 27.0%.

Four of those five sit in the Northeast's famously congested airspace corridor, where flights from several major airports converge in a small stretch of sky. At the opposite end, Honolulu's NAS share is just 7.3% — by far the lowest of any airport in this comparison, consistent with Pacific operations largely sitting outside the mainland's interconnected air-traffic-flow system.

Do all airports share the same delay-cause fingerprint?

No. Across the 40 busiest US airports, weather's share of delay-minutes ranges from 2.6% to 8.9%, NAS ranges from 7.3% to 28.8%, and late-arriving aircraft ranges from 19.1% to 50.1%. Each airport has a distinct fingerprint, shaped by its climate, its place in the national airspace, and how its schedule is built.

A quick way to read any airport's fingerprint:

1. Compare its weather share to the 6.1% national rate — a higher number usually points to a climate more exposed to severe storms or winter weather.

2. Compare its NAS share to the 20.4% national rate — airports in the busiest, most congested airspace, especially the Northeast corridor, tend to run higher.

3. Compare its late-aircraft share to the 39.3% national rate — a high number means delays cascade from earlier flights on the schedule; a low number often shows up at airports built around one carrier's tightly managed hub.

Reagan National (DCA) posts the highest late-aircraft share of any major airport, at 50.1% — half of its delay-minutes trace back to an inbound aircraft that was already running behind. Dallas Love Field (DAL) is close behind at 49.6%. Both post schedules where an earlier flight's lateness ripples forward directly: Love Field is served by just three airlines, led by Southwest, while Reagan National's departures lean heavily on regional partners like PSA Airlines, an American Eagle carrier.

At the other end, Delta's largest hubs post the lowest late-aircraft shares in this comparison — Detroit (DTW) at 19.1% and Minneapolis–Saint Paul (MSP) at 19.8% — but the highest air-carrier shares, at 51.9% and 50.0%. The same pattern shows up at Salt Lake City (SLC) (49.2% carrier, 26.2% late-aircraft) and Honolulu, where Hawaiian Airlines' dominance produces the highest air-carrier share of any airport measured, at 55.8%.

See how these and other major airports stack up overall on our most delayed airports leaderboard.

Frequently asked questions

Which US airports have the most weather-related delays?

Among the 40 busiest US airports, Washington Dulles (IAD) has the highest weather-coded delay share at 8.9% of delay-minutes, followed by Chicago O'Hare (8.5%), Dallas Fort Worth (8.4%), and Minneapolis–Saint Paul and Charlotte Douglas, tied at 8.2%. All five run well above the 6.1% national rate, based on 14.1 million flights from June 2024 through May 2026.

What does NAS delay mean, and which airports have the most?

A National Airspace System (NAS) delay covers non-extreme-weather, air-traffic-control-driven slowdowns — ground stops, gate holds, and traffic-flow restrictions that can originate hundreds of miles away. Indianapolis has the highest NAS share among major airports at 28.8%, followed by JFK (28.1%), LaGuardia (27.6%), Boston Logan (27.1%), and Newark (27.0%) — all well above the 20.4% national rate.

Do all airports have the same delay causes?

No. Weather's share of delay-minutes ranges from 2.6% at Phoenix to 8.9% at Washington Dulles; NAS ranges from 7.3% at Honolulu to 28.8% at Indianapolis; and late-arriving aircraft ranges from 19.1% at Detroit to 50.1% at Reagan National. Each airport's mix reflects its climate, its position in the national airspace, and how tightly its schedule is built.

Is late-arriving aircraft a bigger problem at hub airports?

Not consistently. Reagan National and Dallas Love Field, both mid-sized airports leaning on one dominant operator, post the highest late-aircraft shares (50.1% and 49.6%). But Delta's largest hubs — Detroit and Minneapolis–Saint Paul — post the lowest (19.1% and 19.8%), with more of their delay-minutes coded to air carrier instead. Hub status alone doesn't predict which cause dominates.

Which airport has the fewest weather-related delays?

Phoenix Sky Harbor has the lowest weather-coded delay share of any major US airport, at 2.6% of delay-minutes — less than a third of Washington Dulles's 8.9%. Las Vegas, Boston Logan, and Portland follow closely, each at 2.8%, rounding out the airports least affected by weather in this comparison.

Where does this delay-cause data come from?

Every figure comes from the US Department of Transportation's Bureau of Transportation Statistics On-Time Performance data, covering 14.1 million flights from June 2024 through May 2026. Airport-level splits are flight-weighted averages across each airport's routes, shown only where an airport has more than 1,000 total delay-minutes on record. Full methodology is on our methodology page.