A turbine airfoil (10) usable in a turbine engine and having an internal cooling system (14) with a leading edge impingement channel (16) for enhanced cooling of the leading edge (18) of the turbine airfoil (10) without a leading edge film cooling showerhead array is disclosed. The internal cooling system (14) may include an leading edge cooling supply channel (20) formed from a leading edge wall (22) having a leading edge tip (24) that is advanced closer to an inner surface (26) of the leading edge (18) of the generally elongated, hollow airfoil (28) than other aspects of the leading edge cooling supply channel (20). The leading edge cooling supply channel (20) may include leading edge impingement orifices (30) for directing cooling fluids to impinge on the inner surface (26) of the leading edge (18) of the airfoil (28). The internal cooling system (14) may also include one or more nearwall ribs (92) with impingement orifices (90) in the leading edge cooling supply channel (20) for providing additional cooli
