Tracked live by the FAA, but its flight plan was first seen after takeoff, so we don't know the scheduled time and can't say whether it's late.

UNITED · FLIGHT UA 1538 LANDED 4:22 PM ET, ~19 MIN LATE · SCHEDULED TIME UNKNOWN

UA 1538 · CMH → IAD

took off 3:24 PM ET · landed 4:22 PM ET (scheduled time unknown)
Forecast issued Tue 10:00 PM ET · 7h after departure

Odds over time

Arrive at IAD more than 15 minutes late?
24% chance · ±0 pts +6 pts · 24h
HOW SURE WE ARE Very high. The odds now come almost entirely from live conditions.
WEATHER FORECASTS LIVE IN THE AIR 0% 10% 20% 30% 40% 1.0d 12h 6h Departs Lands