Power law and linear shear
The wind-profile power law is V(h) = Vref (h/href)α. With the common 1/7 exponent, a 20-knot wind at 30 feet becomes about 33 knots at 1,000 feet. The linear alternative, used when a pilot or a forecast quotes a shear in knots per 100 feet, is simply V = Vref + (dV/dh)(h − href). A negative shear (wind decreasing with height) is allowed; the page will not report a negative wind speed.
Neither profile is a microburst. Low-level wind shear in the AIM and in AC 00-54 can be a sudden, localized change associated with a thunderstorm, a front, or a land/sea breeze — not a smooth 1/7 curve. Use this page to turn a surface wind into a rough wind at pattern altitude, or to apply a quoted gradient, and treat convective shear as a weather-avoidance problem. Related tools: the wind triangle, the crosswind component, and the flash-to-bang range estimate.
Sources
- Wind-profile power law, including the 1/7-power law; IEC 61400-1 and standard meteorological / engineering references.
- FAA Aeronautical Information Manual 7-1-24, Wind Shear.
- FAA Advisory Circular 00-54, Pilot Windshear Guide (conceptual; this page does not model a microburst).
Frequently asked questions
Why is the default exponent 1/7?
It is the usual neutral-stability rule of thumb over relatively smooth terrain. It is not a universal constant; type a different α if you have a better estimate for the site.
Can I use this for a microburst or an LLWS alert?
No. Those are abrupt, localized changes. This page only applies a smooth power-law or linear profile.
What reference height should I use for a METAR wind?
A standard anemometer height is 10 metres (about 33 feet). Thirty feet is a close aviation stand-in.