Summer Thunderstorm Flight Delays: Which US Airports Suffer Most
Summer is when US flights run latest. July has the highest delay rate at 18 of the 22 airports DelayGuard publishes full guides for. For June to August, Miami (MIA) runs worst at 35.1% of departures arriving 15 or more minutes late, followed by Orlando (MCO) (34.6%) and Fort Lauderdale (FLL) (33.5%). Salt Lake (SLC) is the calmest at 19.5%. Figures are BTS data for 2,886,219 summer departures, January 2023 to December 2025.
Delay window: January 2023 to December 2025. Cancellation window: 2024 to 2025. Last updated: 2026-10-01. Delayed means a flight arrived 15 or more minutes after its scheduled arrival, the BTS and DOT on-time standard. Cancelled and diverted flights are excluded from delay rates. Historical BTS figures are separate from DelayGuard's per-flight model probability and from live FAA, weather and ground-delay status.
Last reviewed: 2026-10-01.
What breaks in summer
Thunderstorms build through the afternoon over most of the country in summer. Each storm cell forces air traffic control to reroute or hold flights, and the FAA may slow arrivals into an airport with a ground delay program or stop them with a ground stop.
The hourly data shows the knock-on effect. Averaged across the 22 guide airports, 11.5% of flights scheduled before 8 AM arrived late over the full year, against 29.0% after 8 PM. BTS attributes much of that build-up to late-arriving aircraft: a previous flight with the same aircraft arriving late.
Booking rules for June to August
Book the first departure of the day. The earliest hours carry the lowest delay rates at every airport DelayGuard covers, and a morning flight has not yet inherited the day's delays.
Avoid the last bank of the evening, and avoid tight connections at the airports at the top of the table below. A missed connection costs more than a late arrival.
Airport table
Delay rate in June to August vs the rest of the year| Airport | June to August delayed 15+ min | Flights | Other months | Gap (points) | June to August cancelled | Other months cancelled | Worst month |
|---|
| Miami (MIA) | 35.1% | 75,397 | 24.5% | +10.6 | 2.64% | 1.13% | July (36.7%) |
| Orlando (MCO) | 34.6% | 115,814 | 23.1% | +11.5 | 1.72% | 1.34% | July (38.1%) |
| Fort Lauderdale (FLL) | 33.5% | 60,897 | 25.5% | +8.0 | 2.42% | 1.15% | July (34.6%) |
| Charlotte (CLT) | 33.4% | 152,243 | 22.0% | +11.4 | 2.49% | 1.20% | July (38.5%) |
| DFW | 33.0% | 240,845 | 24.3% | +8.7 | 2.20% | 2.35% | June (36.3%) |
| Denver (DEN) | 31.7% | 240,826 | 22.2% | +9.5 | 1.01% | 0.92% | June (33.8%) |
| Philadelphia (PHL) | 30.8% | 77,931 | 20.3% | +10.5 | 3.54% | 1.22% | July (34.8%) |
| O'Hare (ORD) | 30.2% | 227,217 | 22.1% | +8.1 | 1.92% | 1.42% | July (34.3%) |
| Houston Intercontinental (IAH) | 30.2% | 87,293 | 20.9% | +9.3 | 2.60% | 1.33% | July (33.9%) |
| Newark (EWR) | 29.8% | 91,713 | 21.4% | +8.4 | 4.44% | 1.87% | July (36.5%) |
| JFK | 28.8% | 88,428 | 21.0% | +7.8 | 3.98% | 1.21% | July (33.0%) |
| Harry Reid (LAS) | 28.0% | 139,199 | 21.6% | +6.4 | 1.11% | 0.72% | July (31.5%) |
| Atlanta (ATL) | 27.7% | 254,676 | 18.7% | +9.0 | 2.09% | 0.90% | July (32.3%) |
| Logan (BOS) | 26.7% | 109,379 | 20.8% | +5.9 | 2.44% | 1.24% | July (30.6%) |
| LaGuardia (LGA) | 25.9% | 110,646 | 18.9% | +7.0 | 5.34% | 1.75% | July (30.6%) |
| Sea-Tac (SEA) | 25.8% | 140,324 | 19.2% | +6.6 | 0.94% | 0.97% | June (26.4%) |
| Detroit (DTW) | 23.4% | 98,664 | 17.8% | +5.6 | 1.68% | 0.84% | July (26.4%) |
| Minneapolis (MSP) | 23.1% | 97,465 | 16.5% | +6.6 | 1.28% | 0.69% | July (25.7%) |
| Sky Harbor (PHX) | 22.7% | 132,276 | 18.0% | +4.7 | 0.79% | 0.62% | July (25.2%) |
| SFO | 22.4% | 106,741 | 20.2% | +2.2 | 1.06% | 1.02% | March (24.2%) |
| Los Angeles (LAX) | 21.2% | 151,296 | 17.3% | +3.9 | 1.03% | 0.65% | July (22.7%) |
| Salt Lake (SLC) | 19.5% | 86,949 | 15.7% | +3.8 | 0.96% | 0.43% | July (21.3%) |
Predict your flight
Questions
- What is the worst month for flight delays?
- July has the highest delay rate at 18 of the 22 major US airports DelayGuard covers in full, using BTS data from January 2023 to December 2025.
- Which airport has the most summer delays?
- Miami (MIA): 35.1% of June to August departures arrived 15 or more minutes late, against 24.5% in the other nine months.
- What time of day is best to fly in summer?
- Early morning. Delay rates are lowest in the first hours of the day at every airport on this page and rise through the evening.
- Can I check my own flight?
- Yes. The DelayGuard predictor gives a model probability for your route that combines history, weather and FAA data. It is an estimate, not a guarantee.