THE AWOS CAN ONLY RPT ON WX DIRECTLY OVERHEAD AND ONLY UP TO 12000 FT. THIS RPTR ENCOUNTERED ICING IN THE CLOUDS DURING A DSCNT AND APCH AT ORD WHEN HE THOUGHT THAT THE WX WAS GOING TO BE GOOD BASED ON AN ATIS RPT. THE WX DIRECTLY OVER THE ARPT WAS ACCURATE; BUT THE RPT DID NOT REFLECT THE CONDITIONS IN THE VICINITY OF THE ARPT.

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THE AWOS SYS APPEARS TO BE A FINE SYS FOR MANY SMALL AND MEDIUM SIZE ARPTS. HOWEVER; ITS USE AT MAJOR ARPTS; LIKE ORD; ETC; SEEMS TO BE A MAJOR STEP BACKWARDS IN WX SVC AND INFO TO AVIATORS AT THESE HIGH DENSITY FACILITIES. THE SYS'S LIMITATION OF ONLY PROVIDING WX OBSERVATIONS BELOW 12000 FT IS INCONVENIENT AT LEAST AND UNSAFE AT WORST. IT'S INCONVENIENT BECAUSE MOST MAJOR AIRLINES INFORM THEIR PAX OF THE WX AT THEIR DEST. ATIS INFO IS OFTEN THE FINAL WX SOURCE FOR THAT USED BY PLTS IN BRIEFING THE PAX; AND IN THEIR FINAL DSCNT AND APCH PLANNING. ATIS INFO 'SKY CLR BELOW 12000' IS VAGUE. IT COULD MEAN ANYTHING FROM OVCST SKIES ABOVE 12000 FT TO BLUE SKIES (IE; UNLIMITED CEILING). WORST OF ALL IS THAT UNRPTED CLOUDS ABOVE 12000 FT WHEN COMBINED WITH OTHER SIGNIFICANT; AND POSSIBLY UNRPTED CONDITIONS; COULD CREATE UNSAFE FLT CONDITIONS THAT PLTS MUST BE AWARE OF. IMMEDIATELY COMING TO MIND ARE MOISTURE LEVELS AND TEMPS IN ABOVE 12000 FT CLOUDS WHICH COULD RESULT IN SIGNIFICANT ACFT ICING CONDITIONS. ADDITIONALLY; VIRGA FROM CLOUDS ABOVE 12000 FT COULD BE A KEY INDICATOR THAT WINDSHEAR CONDITIONS EXIST. AWOS MAY FALL SHORT IN AREAS SUCH AS ILLUSTRATED IN THESE EXAMPLES. THEREFORE; RECOMMEND A THOROUGH REVIEW BE MADE OF THE USE OF THE AWOS AT ALL ARPTS; AND ESPECIALLY MAJOR FACILITIES. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS RPTR FLIES A B737-200 FOR AN ACR. HE OPERATES PRIMARILY ON THE EAST COAST. IN THIS CASE; THE RPTR WAS TOLD BY THE ATIS THAT THE ARPT AT ORD WAS CLR OF CLOUDS; BUT UPON ARR HE FOUND THAT THERE WERE CLOUDS; WITH ICING ABOVE 12000 FT. THE AWOS SYS AT ORD; BY DESIGN; DOES NOT RPT CLOUDS ABOVE 12000 FT. HE ALSO FOUND THAT THE SYS IS INCAPABLE OF RPTING WX AFFECTING THE ARPT APCH COURSES SINCE IT CAN ONLY 'SEE' WX THAT IS DIRECTLY ABOVE ITS LOCATION. IT CANNOT WARN OF WX MOVING TOWARD THE ARPT OR ANY TREND INFO. THIS LATTER INFO MUST COME FROM A MANUAL OBSERVER EITHER SOMEONE FROM THE NWS OR A TRAINED CONTRACT PERSON OR TRAINED ATC PERSONNEL. THE RPTR SAID THAT HE FELT THAT ICING CONDITIONS DURING STAR OR SID PROCS AND WX TRENDS AT THE ARPT SHOULD BE XMITTED VIA ATIS OR THE CTLRS IN A TIMELY MANNER. HE SAID THAT WE SEEM TO BE PROVIDING LESS SVC TO THE USERS WITH THIS SYS.