WX RPTING EQUIP PROB AUTOMATED SURFACE OBSERVATION SYS UNABLE TO UPDATE CORRECT WX DURING RAPIDLY CHANGING WX CONDITIONS.

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ASOS INSTALLED AT THE FSM ARPT AND COMMISSIONED ON AUG/MON/94. ON AUG/WED/94 ASOS RPTING VISIBILITY AS 2 1/2 MI; BUT TWR VISIBILITY 4 MI. ACCORDING TO REGS WHEN VISIBILITY IS 4 MI OR LESS; TWR VISIBILITY IS THE OFFICIAL VISIBILITY FOR THE ARPT. WITH THE ASOS RPTING VISIBILITY (DIFFERENT FROM TWR VISIBILITY) IT AUTOMATICALLY RPTS THE ASOS VISIBILITY AND THAT BECOMES OFFICIAL WHICH IS CONTRARY TO THE REGS. IN THIS CASE; ASOS VISIBILITY MADE THE CLASS D SURFACE AREA IFR WHEN IN ACTUALITY IT WAS VFR. BY MAKING THE CLASS D SURFACE AREA IFR FLYING IS RESTR. NO PROVISION WAS MADE IN THE ASOS SYS TO RPT TWR VISIBILITY OTHER THAN IN REMARKS OR IF THE TWR VISIBILITY IS LESS. SINCE TWR VISIBILITY IS THE OFFICIAL VISIBILITY FOR THE ARPT WHEN THE VISIBILITY IS 4 MI OR LESS; THE PROCESS OF RPTING AND DISSEMINATING THE VISIBILITY THROUGH THE ASOS NEEDS TO BE CHANGED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: TWR SUPVR SAID GENERALLY THE ASOS WORKS GOOD. DURING RAPIDLY CHANGING WX CONDITIONS; IT WILL NOT UPDATE ITSELF FAST ENOUGH. INCORRECT VISIBILITY IS BEING RPTED. NWS PERSONNEL WILL NOT AUGMENT THE SYS AND MAKE THE UPDATE.