Flight level winds to Surface winds


When I have read reconnaissance reports from different storms, I have always noticed a remark "Maximum flight level wind 75 kt" etc. Wondering, how to convert flight level winds to surface wind? Does it depend from height of the plane?

Best wishes,
Good day, Tarmo, this is Chris Collura...

In hurricane recon flights, a common correction is 90% from the standard 5,000 to 10,000 foot flight level winds. This is as in MOST cases (where there is good boundary layer mixing, convection, etc).

In other words, a 75 knot flight level wind woudl correlate to (90 %) of that which is 75 x .90 = 67.5 knots.

Also, to convert KNOTS to MPH, multiply knots by 1.15. In the above example, 67.5 knots (x 1.15) gives a surface wind of about 77.6 MPH.

Chris C - KG4PJN
Does anyone know why you can use the same formula for different flight levels? I know this is a common practice, but I don't know the reasoning behind it.

Tarmo, welcome. First stormtrack member from Estonia. Very cool.