How are winds aloft used in NavLog calculations?

Wind Aloft information is derived from the ForeFlight Global Winds engine.  This allows us to provide winds aloft forecasts for any point on the planet up to 54,000′ (FL540).  ForeFlight Mobile will compute the wind impact for any route of flight: flight plans using airways, SIDS, STARs, known airports, any waypoint pairs, and even a string of custom user waypoints or lat/long entries.

The ForeFlight Global Winds engine blends observed data from the National Weather Services and computer model data for the entire planet.  The engine produces forecast grids of winds, temperatures, turbulence, and icing covering the entire world, making them applicable for planning any length of flight anywhere on the planet.  Forecasts are updated four times each day by processing output from the National Weather Service’s Global Forecast System (GFS) numerical weather prediction model through a suite of custom algorithms to improve usability for aviation planning operations.

The GFS model itself is a state-of-the-science computational fluid dynamics (CFD) code that incorporates a plethora of global weather observations collected by a variety of surface, aircraft, and satellite-based platforms.  Via advanced data assimilation techniques, these observations are used to create a three-dimensional gridded analysis of the state of the atmosphere.  Then, a large supercomputing system advances the basic weather elements forward in time via a complex set of differential equations that describe momentum, heat, and moisture changes as a function of time, producing global grids of forecast data on a grid covering the entire world with 0.5-degree latitude/longitude spacing.

The raw data grids are received from the NWS and complex algorithms are applied to compute additional parameters such as turbulence and icing potential and converts the output from meteorological coordinates to flight levels used by aviators of all types.

In the NavLog, we take that interpolated wind data at the different positions and altitudes and calculate your projected groundspeed (and thus, time and fuel-burn) on different segments based on the climb & cruise performance numbers you enter. For example, if you're climbing to 9000' and the winds at 3000', 6000' and 9000' are dramatically different, we take that into account in the calculations for how long you'll be in the climb, cruise & descent phases.

Further, if there is a long leg, we internally break it up into smaller segments and calculate the wind effect in each segment.  If legs are all in the 40-60nm range, then we don't break them up.