There are multiple different factors that affect Winds Aloft information for your route within ForeFlight:
1. Winds aloft are only incorporated if a true airspeed and altitude are provided as part of the route.
2. Selected Time of Departure (ETD) - ForeFlight will use this time to incorporate the proper winds aloft forecasts into your time and fuel usage calculations. If you don’t provide a time, ForeFlight Mobile assumes you are departing ASAP. If you select an ETD that is beyond the forecast period for upper winds, then no upper winds data will be provided.
3. Selected Altitude - Winds aloft will be provided based on the altitude you choose from the Altitude Advisor. To see your route without wind adjustments input an altitude that is too high in the route search, such as 80,000'. That will override any altitude in the default aircraft and prevent the calculations.
4. Winds Aloft calculations require an active network connection to retrieve the latest winds aloft forecast. However, once a forecast has been downloaded it will be saved for a few hours for use when offline (in-flight).