Every flying day uses the NWS winds-aloft forecast for tomorrow. Transit legs are flown at whichever allowed altitude gives the shortest time (sampled at five points along the leg). Collections are flown at the set height above the site's ground elevation. Survey line headings aren't known, so the collect penalty averages passes flown both ways at every heading. Wind at a point blends the four nearest forecast stations. Climb, descent and temperature effects on true airspeed aren't modeled.
Paste a newer forecast
On aviationweather.gov open Data → Winds/Temps, pick the region (for example San Francisco, Salt Lake City) and the 24-hour forecast, and copy the whole text block, from the “DATA BASED ON” line through the last station. Pasted stations replace embedded ones with the same ID.