Runways are listed according to Magnetic North and winds are displayed according to True North. To determine the crosswinds and headwind components, you will need to convert the runway magnetic orientation to a True North orientation.
To do this, take the magnetic runway heading and add or subtract the appropriate amount of Magnetic Variation. If the variation is E, add it. If it is W, subtract it. You can find the magnetic variation for the airport on the AIRPORTS page under the INFO tab and FEATURES. Also, if winds are in mph, you will need to convert that to knots. You can then take all those values and enter them into an E6B.
As you will see, the numbers displayed in ForeFlight are correct. If you have any further questions about this, please email our Pilot Support Team.
Example:
In Image 1, one might think the crosswind for runway 26 at KSNS should be from the right. The thinking would be that the runway is oriented as 264 degrees and the wind is 270 degrees, so the 1 kt crosswind component should be from the right.
Image 1: Common case of thinking crosswind component is not correct
The above thinking would not be correct because they did not convert the the runway from Magnetic to true. Here is what needs to be done.
First, find the magnetic variation for the airport. In this case, KSNS has a Magnetic Variation of 13 degrees E. The magnetic heading for runway 26 is 264 degrees (Found on the Airport page under the More tab and Features). Since the magnetic variation is East, it is added to the magnetic runway heading. Here is the formula:
264 Degrees Magnetic (Runway) + 13 Degrees East (Magnetic Variation) = 277 degrees True
Any wind coming from an orientation of less that 277 degrees true (276 - 098) will have a left hand component. In this example, the winds are listed as 270 degrees True at 14 mph (12.2 knots)
Using an online E6B for winds, if we plug in those numbers, we get a left crosswind of 1 kt and a headwind of 12 kts, which is what ForeFlight is showing.
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