UNAUTH TKOF WHEN ARPT WX MINIMUMS FOR TKOF DID NOT EXIST. PART TIME ATCT. ATCT CLOSED.

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FLT TAXIED OUT AND DEPARTED AZO WITH WX AT 1/4 MI VISIBILITY DUE TO PATCHY GND FOG. THIS WX WAS RECEIVED FROM XYZ AIRLINES WX OBSERVER PRIOR TO TAXI. AS PER OPS SPECS; XYZ IS THE APPROVED WX SOURCE WHEN AZO TWR IS NOT IN OP AS WAS THE CASE PRIOR TO XA00 LCL TIME ON JUL/XX/93. WE ARE ALSO ALLOWED TO DEPART WITH 1/4 MI VISIBILITY PER THE OPS SPECS. DURING TAXI TO RWY AT APPROX AM50 LCL; THE CTLR IN THE TWR; THOUGH NOT OFFICIALLY OPEN YET; CALLED AND GOT OUR CLRNC FROM AZO DEP WHICH HAD ASSUMED CTL OF ITS AIRSPACE FROM ZAU A FEW MINS EARLY THAT MORNING. THE CTLR SAID TO CALL DEP WHEN READY FOR TKOF TO RECEIVE OUR IFR RELEASE TIME. THIS METHOD OF RECEIVING THE CLRNC SEEMS TO BE COMMON PRACTICE AS IT HAS HAPPENED MANY TIMES BEFORE AT AZO. PLEASE NOTE THAT NO WX UPDATE WAS GIVEN AT THIS TIME. AFTER COMPLETING THE APPROPRIATE CHKLISTS; WE CALLED DEP AND RECEIVED AN IFR RELEASE AND WAS INSTRUCTED TO CALL THEM AIRBORNE. UPON TAKING THE RWY; IT WAS MY OPINION THAT A 1/4 MI VISIBILITY DID EXIST. I WAS ABLE TO SEE MULTIPLE RWY EDGE LIGHTS (APPROX 4-5 SETS) AND MULTIPLE CTRLINE SEGMENTS WHICH AFFORDED ME ADEQUATE VISUAL REF REQUIRED FOR A LEGAL REDUCED VISIBILITY TKOF. THE GND FOG DENSITY WAS HIGHLY VARIABLE DEPENDING UPON LOCATION. DURING RIDE FROM HOTEL; VISIBILITY RANGED FROM NEAR 0 IN SPOTS TO APPROX 1 MI IN SPOTS. LIFTOFF OCCURRED AT AM55 LCL TIME AND A NORMAL FLT TO DTW FOLLOWED. MID-FLT TO DTW; ZOB REQUESTED OUR ACFT TAIL NUMBER FOR AZO APCH. WE COMPLIED. I THEN REQUESTED AND RECEIVED A PHONE NUMBER TO CALL AFTER LNDG. THE CALL WAS MADE TO A MR. X WHO IDENTED HIMSELF AS THE SUPVR OF AZO ATC. HE INFORMED ME THAT WE HAD DEPARTED WITH A 1/16 MI VISIBILITY AND WAS REQUIRED TO INFORM THE LCL ACR DISTRICT OFFICE. DURING THE CONVERSATION THAT FOLLOWED; I EXPLAINED WE HAD HARD COPY WX INDICATING A 1/4 MI AND HAD NEVER BEEN INFORMED OF A CHANGE. MR. X SAID THAT THE TWR EMPLOYEES TOOK A WX OBSERVATION SHORTLY AFTER AM45 AND SENT THE INFO TO XYZ. HE ALSO SAID THAT HE HAD PULLED THE TWR TAPES AND DISCOVERED THE CTLR WHO GAVE US OUR CLRNC; NEVER RELAYED THIS NEW WX AS HE SHOULD HAVE. ALSO NOTE; THE DEP CTLR WHO GAVE US OUR IFR RELEASE MENTIONED NOTHING ABOUT ANY NEW WX OBSERVATION. MR. X TOLD ME THAT HE THOUGHT WE DID NOTHING WRONG IN LIGHT OF THE ABOVE INFO BUT HE WAS STILL REQUIRED TO NOTIFY THE FAA. IT WAS AT THE TIME AND STILL IS MY BELIEF THAT 1/4 MI VISIBILITY EXISTED WHEN I BEGAN MY TKOF ROLL AT AZO. HAD I BEEN INFORMED BY EITHER THE TWR OR DEP CTLR THAT A WX OBSERVATION INDICATED THAT THE AZO WX WAS 1/16 MI AND FOG AT THE TIME OF THE OBSERVATION; FLT WOULD HAVE PROMPTLY RETURNED TO THE GATE TO AWAIT IMPROVEMENT IN THE RPTED CONDITIONS. FURTHER INVESTIGATION BY COMPANY OFFICIALS HAVE DISCOVERED THAT THIS IS AN INTERNAL PROB THAT AZO ATC OFFICIALS ARE INVESTIGATING AND TRYING TO PREVENT DUE TO SLOW COM.