map = Basemap(projection='cyl',llcrnrlat=lowerllat,urcrnrlat=upperrlat,
                    llcrnrlon=lowerllon,urcrnrlon=upperrlon,
                        resolution='h')
# lllat, urlat,lllon, urlon set outside of f(x) lower left and upper right lat/lon for basemap axis limits

x, y = map(lons[:,:], lats[:,:])
map.contourf(x, y, U_10m, vmin=0, vmax=20)

parallels = np.arange(-85.,85,1.)
meridians = np.arange(-180.,180.,1.)
map.drawcoastlines(linewidth = 2, color = '0.15')
map.drawparallels(parallels,labels=[False,True,True,False])
map.drawmeridians(meridians,labels=[True,False,False,True])
cbar = plt.colorbar(boundaries=np.linspace(0,1,20))
cbar.set_label('10m U (m/s)', size=20)
cbar.set_clim(0, 20)

#failed attempt:
cbar = plt.colorbar.ColorbarBase(ax, cmap=cm,
#                 norm=plt.colors.Normalize(vmin=0, vmax=20))
#AttributeError: 'function' object has no attribute 'ColorbarBase'#