AN ACR CANADAIR CL65 MADE A DSNDING TURN TO FINAL IN FRONT OF A SIKORSKY SK76 HELI TRANSITING THE AREA IN LEVEL FLT. THE APCH CTLR HAD NOT CONSIDERED THE STRONG WIND DRIFT WHEN HE PREVIOUSLY ISSUED A HEADING CHANGE TO THE HELI TO PREVENT THIS FROM HAPPENING.

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CARJ WAS INBOUND FROM W FOR VISUAL APCH TO RWY 24. HELI WAS ON A LIFEGUARD FLT TO A HOSPITAL SW OF XYZ FROM THE NE AT 2000 FT MSL. I ALSO HAD A DHC8 INBOUND FROM THE SW; SO I ISSUED THE SK76 A 260 DEG HDG TO GET IT AWAY FROM THE CTRLINE OF RWY 24. WINDS ALOFT WERE 310 DEGS AT 40 KTS AND HEADING WAS INEFFECTUAL. THE RADAR IN THE TWR IS AT SUCH A RANGE AT NIGHT AND RESOLUTION IS SO POOR THAT I WAS NOT ABLE TO DISCERN THE CONFLICT UNTIL I SAW IT OUT THE WINDOW. (IE; THAT THE 260 DEG HDG WASN'T WORKING.) THE CARJ HAD BEEN TOLD TO MAINTAIN 2500 FT UNTIL TURNING FINAL; AND ENDED UP DSNDING RIGHT IN FRONT OF THE SK76. THE SK76 HAD RPTED THE CARJ IN SIGHT; 'MAINTAIN VISUAL;' BUT IT WAS MUCH CLOSER THAN I WOULD HAVE LIKED. I MIGHT HAVE OBTAINED WIND ALOFT FROM THE CARJ AND ISSUED A MORE EFFECTIVE VECTOR OR SLEWED MY RANGE IN BRIEFLY TO GET A BETTER SENSE OF WHAT HEADING THE SK76 WAS TRACKING. I WAS ALSO FEELING PRESSURE NOT TO TAKE A MEDEVAC TOO FAR OFF ITS FLT PATH -- THIS WAS A CONTRIBUTING FACTOR.