In this work we relate uncertainty in background roughness length (z0) to uncertainty in wind speeds. where the latter are predicted at a wind farm location based on wind statistics observed at a different site. Sensitivity of predicted winds to roughness is derived analytically for the industry-standard European Wind Atlas method. which is based on the geostrophic drag law. http://yeswellneses.shop/product-category/multiminerals-multivitamins/