COMMUTER MDT REQUESTED A STRAIGHT IN CONTACT APCH TO COU WHEN WX WAS BELOW VFR MINS AND THE ACFT WAS LOW ON FUEL AND DID NOT WANT TO MAKE A COMPLETE ILS APCH.

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UPON REACHING OUR ORIGINAL DEST AT STL AN UNDERCAST FOG LAYER MOVED IN PUTTING THE ARPT BELOW MINS FOR THE ILS APCH. WE HAD NO ALTERNATE ON OUR DISPATCH AND THEREFORE HAD NOT PUT ON FUEL FOR AN ALTERNATE. WE HAD SPRINGFIELD; IL; WX IN OUR WX PACKAGE AND HAD JUST FLOWN OVER THEIR ARPT AND THE WX LOOKED GOOD SO WE ASKED DISPATCH ABOUT DIVERTING THERE. THEY TOLD US THAT SPI WX WAS COMING DOWN RAPIDLY AND THAT COLUMBIA; MO'S; WX WAS CLR AND 15 MI SO THE CAPT AND DISPATCH AGREED TO DIVERT US TO COLUMBIA. UPON RECEIVING COLUMBIA'S ATIS WE LEARNED THAT PRESENT WX WAS SKY PARTIALLY OBSCURED VISIBILITY 2 MI WITH FOG. BY THIS TIME WE HAD ABOUT 1400 POUNDS OF FUEL AND WE TOLD COLUMBIA APCH UPON CHKING ON WITH THEM WE WERE 'MIN FUEL'. WE WERE GIVEN A CLRNC DIRECT TO THE COLUMBIA VOR AND WITH GOOD CONTACT (VISUAL) WITH THE RWY SURFACE WE CALLED FOR FIELD IN SIGHT. APCH WAS UNABLE TO GIVE US A VISUAL APCH BECAUSE TWR VISIBILITY WAS STILL SHOWING 2 MI. THEY ASKED US IF WE WERE REQUESTING A CONTACT APCH AND THE CAPT INDICATED TO ME THAT HE WANTED ONE. WE DIDN'T HAVE TIME TO DISCUSS IT AT THE TIME BECAUSE WE WERE JUST ABOUT 4 MI FROM THE ARPT AND HAD TO MAKE AN INSTANT DECISION. THE ALTERNATIVE WAS TO SHOOT THE FULL APCH (GOING OUTBOUND AND THEN REVERSE COURSE) SINCE COLUMBIA DOESN'T HAVE RADAR AND THIS MAY HAVE PUT US INTO A FUEL SITUATION WHERE WE WOULD HAVE TO DECLARE AN EMER. SO SINCE OUR SHORT RANGE VISIBILITY WAS GOOD; WE TOOK THE CONTACT TO GET IN MORE QUICKLY.