FLC OF AN LTT ACR ACFT INADVERTENTLY MADE TKOFS AND LNDGS IN A CTL ZONE TFC PATTERN ARPT WITHOUT AN IFR CLRNC.

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DURING MY EMB-120 BRAZILIA TRANSITION FO CHK RIDE; WE MAY HAVE BEEN FLYING IN THE PATTERN WITH LESS THAN 3 MI VISIBILITY BEING RPTED ON AWOS WX SVC. AT NO TIME WAS THE INFLT VISIBILITY ACTUALLY THAT LOW. HOWEVER; LIGHT GND FOG WAS BEGINNING TO FORM; NOT SO MUCH ON THE RWY; BUT TO THE E AND SURROUNDING AREAS. SEEING THE FORMATION OF GND FOG AS WE TAXIED TO THE DEP END OF THE RWY I REQUESTED THE CHK AIRMAN TO CHK THE WX. AT THIS TIME AWOS WAS CALLING VISIBILITY 1 MI. WE BOTH WERE VERY SURPRISED. WE COULD SEE THE ENTIRE LENGTH OF THE RWY AS WELL AS LIGHTS GREATER THAN 3 MI. WITHIN 15 MINS AFTER THE CHK WAS MADE; THE GND FOG BECAME MUCH MORE APPARENT. AFTER BECOMING AWARE OF THE VISIBILITY IFR CLRNCS WERE USED. I HAD COMPLETED ALL PORTIONS OF THE CHK RIDE IN THE SIMULATOR THAT NIGHT AND NEEDED TO FLY THE ACTUAL ACFT THAT NIGHT FOR TKOFS AND LNDGS. I HAD A LOT ON MY MIND DURING THE CHK RIDE BUT WX CONDITIONS REMAINED A PRIORITY. IT IS MY FEELING THAT IN THIS CASE AWOS READINGS DID NOT REPRESENT ACTUAL RWY AND ARPT CONDITIONS DURING A BRIEF TIME OF THE GND FOG FORMATION.