SFOSEP

The weak window here is the middle of the day, not the evening: 11am–2pm runs 75.6% on time against 93.2% for 5am–8am. That shape usually means a departure bank rather than an accumulating delay, so the recovery later in the afternoon is real rather than noise. The 8am–11am window is the busiest, with 2,805 flights scheduled in it.

Across the week, Wednesday is the strongest day at 87.6% on time and Friday the weakest at 78.0%. 10 points is a smaller lever than departure hour, but it is free.

The spread between JetBlue and Southwest is 27 points, wide enough that it should decide the booking. On a hundred trips that is 27 more arrivals inside the on-time window.

42% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 120,000 reported delay minutes here, that single category outweighs weather by 11 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 119,980 reported delay minutes.

Cancellations are rare at 0.25%, below the national 0.51% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.

Badly late arrivals are rare here: only 4.5% land an hour or more behind schedule, against 5.4% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.