There is currently (Thurs 3rd) an area of 160kt jet stream winds positioned over the north-east USA. This would have been positoned over the center of the country previously.
Weather model charts show it as being about 500nm long (E-W) and 200 wide N-S), with much lower speeds outside that region (and at lower altitudes). A flight plan would be able to take advantage of the winds, but the whole route could not be at top speed.