Hi, thanks for the kind words and glad you like SimBrief.
SimBrief’s winds are extracted from the NOAA GFS forecast model. I believe many (perhaps most) flight simulator weather add-ons also use the GFS model, and there is also an option on Windy to view the GFS data in the bottom-right corner.
At any given time, SimBrief stores the historical and forecast winds from 7 days in the past up to ~36 hours in the future. Using forecast winds means greater accuracy when planning long haul flights, since the winds can change significantly over a 15 hour flight.
In other words, when planning a 15 hour long haul flight, SimBrief doesn’t simply use a snapshot of the current global winds. But rather, it will also consider how the winds will shift over the next 15 hours, and gradually transition through the various wind forecasts as the flight progresses (so your descent will be planned using the forecast winds 15 hours from now, rather than the current winds at time of flight planning).
Not sure if this answers your question, but hope this helps!