AN ACR LGT CREW MADE AN APCH AND LNDG AT RNO WHEN THE WX WAS BELOW LIMITS.

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WE WERE FLYING FROM DFW TO RNO WITH AN ETA OF LATE PM17 LCL TIME. THE WX FORECAST FOR RNO WAS BASICALLY CLR (250 SCATTERED) UNTIL EARLY AM00 LCL; THEN 3 MI VISIBILITY WITH FOG. WE HAD NOT FILED AN ALTERNATE AND HAD NO ALTERNATE OR HOLDING FUEL ON BOARD. ENRTE; ACTUAL WX RPTS FROM RNO WERE GOOD; CONFIRMING THE FORECAST. APCHING RNO; ATIS WAS RPTING CLR WITH 10 MI VISIBILITY. AFTER HDOF TO RNO APCH CTL; CTLR INFORMED US THAT NEW ATIS WAS NOW RPTING 2 MI VISIBILITY. I IMMEDIATELY REQUESTED FE TO OBTAIN WX FOR SACRAMENTO; CA (SMF) WHICH IS THE NEAREST ALTERNATE ARPT. SHORTLY THEREAFTER; THE SMF WX CAME IN ON THE ACARS PRINTER: -X 1/4F WITH RVR OF 1000 FT. WE WERE NOW ON DOWNWIND TO RWY 16R AT RNO WITH APPROX 1 HR OF FUEL ON BOARD AND OUR NEAREST ALTERNATE BELOW MINIMUMS. I REQUESTED THE FO TO OBTAIN THE WX FOR SAN FRANCISCO AND OAKLAND; THE NEXT NEAREST ALTERNATES. I REQUESTED AN ILS- DME APCH TO 16R. THE TWR INFORMED US THAT TWR VISIBILITY WAS NOW 2 MI WITH THE RVR LESS THAN 1/4 MI. WE COULD SEE THE APCH LIGHTS FROM 13 MI AWAY. THE TERRAIN SURROUNDING THE ARPT WAS ALL CLR; MOST OF THE CITY WAS CLR; BUT THERE WAS A PATCH OF GND FOG COVERING PARTS OF THE CITY AND MOST OF THE ARPT. WITH NO OTHER GOOD OPTIONS; WE ELECTED TO CONTINUE THE APCH TO SEE HOW THINGS LOOKED ONCE WE GOT DOWN NEAR THE RWY. DECISION HT ON THIS APCH IS 600 FT AGL. TOPS OF THE GND FOG WAS ABOUT 150 FT AGL. WE FLEW THE APCH DOWN TO DECISION HT; THEN ON DOWN TO 200 FT. AS WE GOT OVER THE TOP OF THE APCH LIGHTS; WE COULD SEE THEM AND THE RWY THRESHOLD LIGHTS. CONTINUING ON DOWN TO 100 FT; WE COULD SEE THE RWY LIGHTS SO WE CONTINUED TO LET DOWN TO A NORMAL LNDG AND ROLLOUT. I DIDN'T WANT TO DIVERT THE CTLR'S ATTN UNNECESSARILY TO US. THIS WAS MY THINKING AT THE TIME IN NOT DECLARING AN EMER.