Today: DL 4070 at 11:59 is the safest bet, 16% chance of being 15+ min late; evening flights run 22–33%.

Safest bet today DL 4070 ONT 11:59 → SEA 14:51 · 16% chance 15+ min late · usually 91% on time Riskiest F9 2275 ONT 16:49 → SEA 19:38 · 33% chance 15+ min late · usually 80% on time

Against a calm day 24% average chance a nonstop arrives 15+ min late; 19% for the same flights on a calm-weather day

Every nonstop today

12-month record →

Ranked by the chance of arriving 15+ minutes late, with each flight’s on-time record over Aug 2025 – Jul 2026 beside it. Times are local. Pick a flight for its forecast. Click a column to sort. 2 flights that already left today are not shown.


DL 4070 Delta flown by SkyWest Flight history →	ONT 11:59	SEA 14:51	16%	5%	0.4%	91%
AS 475 Alaska	ONT 11:13	SEA 13:51	17%	4%	1.2%	no record
AS 654 Alaska Flight history →	ONT 12:08	SEA 14:48	20%	4%	1.1%	90%
DL 4031 Delta flown by SkyWest Flight history →	ONT 18:01	SEA 20:50	22%	6%	0.6%	90%worse than usual
AS 567 Alaska Flight history →	ONT 14:05	SEA 16:45	23%	5%	1.2%	77%
AS 594 Alaska Flight history →	ONT 21:20	SEA 23:59	25%	6%	0.7%	67%
AS 575 Alaska Flight history →	ONT 14:10	SEA 16:47	26%	7%	1.2%	61%
AS 592 Alaska Flight history →	ONT 18:56	SEA 21:33	31%	7%	1.2%	71%
F9 2275 Frontier Flight history →	ONT 16:49	SEA 19:38	33%	10%	1.0%	80%worse than usual

How these are worked out. Each flight’s odds are our forecast for that day; flights of airlines we don’t forecast yet use their 12-month record and are marked. Makes the connection: the first flight’s 12-month lateness curve, scaled so its chance of arriving 15+ min late matches the day’s forecast, at the layover minus the 45-minute minimum (90 on separate tickets). Arrives on time: first flight not cancelled × connection made × second flight not cancelled × second flight within 15 minutes, each from the day’s forecast.

About this data: forecast odds from our model for Sun, Oct 4 (newest published update); 12-month records from US DOT on-time data, Aug 2025 – Jul 2026, all US airlines; regional flights count under the airline that sells them. JSON