Data, acquired by specially instrumented aircraft, are presented for two levels through a northwesterly jet stream. Wind shear on the cyclonic side of this jet stream is roughly twice that on the anticyclonic side. Stronger areas of clear air turbulence appear closely related to strong vertical wind shear. An area of uniform absolute vorticity exists for about 160 nautical miles north of the jet stream. Measured microvariations of the temperature along a pressure surface—up to 3.1 C° in 8.5 nautical miles—give indirect evidence of jet stream “fingers” of high velocity.