Today looks rough: weather pushes the average chance of arriving 15+ min late to 59%, against 34% on a calm day. Safest: UA 1218 at 18:02, 39%.

Safest bet today UA 1218 SEA 18:02 → DEN 21:44 · 39% chance 15+ min late · usually 84% on time Riskiest AS 602 SEA 13:16 → DEN 16:52 · 79% chance 15+ min late · usually 76% on time

Weather 59% average chance a nonstop arrives 15+ min late; 34% 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. 9 flights that already left today are not shown.


UA 1218 United Flight history →	SEA 18:02	DEN 21:44	39%	10%	0.2%	84%worse than usual
UA 1351 United Flight history →	SEA 12:50	DEN 16:42	46%	9%	0.2%	89%worse than usual
UA 2033 United	SEA 12:50	DEN 16:50	46%	9%	0.2%	no record
AS 642 Alaska Flight history →	SEA 20:11	DEN 23:59	50%	11%	0.4%	81%worse than usual
UA 325 United Flight history →	SEA 15:41	DEN 19:30	52%	9%	0.2%	86%worse than usual
AS 310 Alaska Flight history →	SEA 19:00	DEN 22:45	54%	14%	0.4%	65%worse than usual
WN 3493 Southwest	SEA 21:16	DEN 00:55	55%	18%	0.1%	no record
UA 333 United Flight history →	SEA 14:34	DEN 18:23	55%	9%	0.2%	66%worse than usual
F9 1176 Frontier Flight history →	SEA 19:06	DEN 22:58	55%	22%	0.9%	78%worse than usual
DL 2851 Delta Flight history →	SEA 19:59	DEN 23:44	56%	19%	0.2%	78%worse than usual
UA 757 United Flight history →	SEA 15:52	DEN 19:33	56%	9%	0.2%	88%worse than usual
WN 3617 Southwest Flight history →	SEA 17:05	DEN 20:45	60%	19%	0.1%	14%
WN 4845 Southwest Flight history →	SEA 20:05	DEN 23:45	60%	19%	0.1%	40%
AS 535 Alaska Flight history →	SEA 11:44	DEN 15:38	65%	9%	0.6%	78%worse than usual
DL 2543 Delta Flight history →	SEA 13:50	DEN 17:43	67%	18%	0.2%	39%
F9 3406 Frontier Flight history →	SEA 16:34	DEN 20:22	67%	22%	1.0%	78%worse than usual
AS 242 Alaska Flight history →	SEA 13:35	DEN 17:22	69%	11%	0.6%	70%worse than usual
WN 1166 Southwest	SEA 14:25	DEN 18:15	72%	15%	0.1%	no record
WN 1860 Southwest	SEA 14:26	DEN 18:00	75%	13%	0.2%	no record
AS 602 Alaska Flight history →	SEA 13:16	DEN 16:52	79%	11%	0.6%	76%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