To amplify on the message from W.Chan, we can state that the CTAS system uses winds in the stereographic projection. An additional rotation term to go from ( lat,long) to NAS Center specific stereographic plane is needed: a good approximate term ( accurate to within .5 degrees everywhere) is sin(latitude of NAS Center tangency point)times the difference in longitude between the coordinate of the wind vector and the longitude of the tnagency point). The rotation listed by Stan Benjamin ( from LC to (lat,long) plus this rotation, from (lat,long) to (x,y)stereographic must be applied. The question raised was more about the stretching of vectors during projections. It seems that NO stetching is applied. That is fine, as long as we know this to be the case, so that we would not "unstretch" vectors when going back from LC to (lat,long) and then stretching again to go to Stereographic. We will treat winds as made up of a scalar for wind strength and a unit vector indicating direction. Thanks.