Today: WN 4128 at 05:00 is the safest bet, 2% chance of being 15+ min late; evening flights run 20%.

Safest bet today WN 4128 STL 05:00 → TPA 08:29 · 2% chance 15+ min late Riskiest WN 4619 STL 20:15 → TPA 23:35 · 20% chance 15+ min late · usually 52% on time

Against a calm day 10% average chance a nonstop arrives 15+ min late; 8% 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.


WN 4128 Southwest	STL 05:00	TPA 08:29	2%	1%	0.2%	no record
WN 3985 Southwest Flight history →	STL 05:00	TPA 08:20	2%	1%	0.2%	95%
WN 3986 Southwest Flight history →	STL 10:05	TPA 13:25	6%	2%	0.2%	91%
WN 4129 Southwest	STL 10:40	TPA 14:09	11%	4%	0.2%	no record
WN 4130 Southwest	STL 19:55	TPA 23:24	20%	9%	0.6%	no record
WN 4619 Southwest Flight history →	STL 20:15	TPA 23:35	20%	7%	0.6%	52%

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 Mon, Oct 5 (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