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 3774 LANDED 12:11 PM PT, ~6 MIN LATE · SCHEDULED TIME UNKNOWN

UA 3774 · STN → SFO

took off 10:06 AM BST · landed 12:11 PM PT (scheduled time unknown)
Forecast issued Wed 10:00 PM ET · 17h after departure

Odds over time

Arrive at SFO more than 15 minutes late?
13% chance · ±0 pts −4 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