Narrative:

Thunderstorms and showers in area. ASOS commissioned in aug/94 and is main reporting system for WX at fsm. ASOS reporting visibility 1 mi with heavy rain. Tower visibility at time is more than 5 mi with no rain. 5 mins later, ASOS reporting visibility 1 3/4 mi with light rain. Tower visibility at the time was 7 mi with light rain. The NWS amended the visibility to 7 mi and light rain after being asked to take a visibility observation to confirm the incorrect readings the ASOS is providing. This is an ongoing problem with the ASOS incorrectly reporting visibility. The ASOS apparently does not have the capability to take prevailing visibility and is greatly affected by short term, local phenomena. It is not unusual for a patch of ground fog to cause the ASOS to report visibility well below what the prevailing visibility is. Because of numerous incorrect readings, we are being forced to ask the NWS to amend sky and visibility readings to reflect actual conditions. After the first of 1995 the NWS office here will close down and we will not have the capability to correct erroneous readings by the ASOS. This is unacceptable since the flying public relies on us for current and correct WX observations. The ASOS system at the very least needs a human backup to correct the errors. A better solution would be to decommission the ASOS and return the job of taking WX observations to the people that have the best view of what the WX is -- the NWS and the controllers.

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Original NASA ASRS Text

Title: WX RPTING EQUIP PROB ASOS RPTING WRONG VISIBILITY AND WX PHENOMENA. ONGOING PROB.

Narrative: TSTMS AND SHOWERS IN AREA. ASOS COMMISSIONED IN AUG/94 AND IS MAIN RPTING SYS FOR WX AT FSM. ASOS RPTING VISIBILITY 1 MI WITH HVY RAIN. TWR VISIBILITY AT TIME IS MORE THAN 5 MI WITH NO RAIN. 5 MINS LATER, ASOS RPTING VISIBILITY 1 3/4 MI WITH LIGHT RAIN. TWR VISIBILITY AT THE TIME WAS 7 MI WITH LIGHT RAIN. THE NWS AMENDED THE VISIBILITY TO 7 MI AND LIGHT RAIN AFTER BEING ASKED TO TAKE A VISIBILITY OBSERVATION TO CONFIRM THE INCORRECT READINGS THE ASOS IS PROVIDING. THIS IS AN ONGOING PROB WITH THE ASOS INCORRECTLY RPTING VISIBILITY. THE ASOS APPARENTLY DOES NOT HAVE THE CAPABILITY TO TAKE PREVAILING VISIBILITY AND IS GREATLY AFFECTED BY SHORT TERM, LCL PHENOMENA. IT IS NOT UNUSUAL FOR A PATCH OF GND FOG TO CAUSE THE ASOS TO RPT VISIBILITY WELL BELOW WHAT THE PREVAILING VISIBILITY IS. BECAUSE OF NUMEROUS INCORRECT READINGS, WE ARE BEING FORCED TO ASK THE NWS TO AMEND SKY AND VISIBILITY READINGS TO REFLECT ACTUAL CONDITIONS. AFTER THE FIRST OF 1995 THE NWS OFFICE HERE WILL CLOSE DOWN AND WE WILL NOT HAVE THE CAPABILITY TO CORRECT ERRONEOUS READINGS BY THE ASOS. THIS IS UNACCEPTABLE SINCE THE FLYING PUBLIC RELIES ON US FOR CURRENT AND CORRECT WX OBSERVATIONS. THE ASOS SYS AT THE VERY LEAST NEEDS A HUMAN BACKUP TO CORRECT THE ERRORS. A BETTER SOLUTION WOULD BE TO DECOMMISSION THE ASOS AND RETURN THE JOB OF TAKING WX OBSERVATIONS TO THE PEOPLE THAT HAVE THE BEST VIEW OF WHAT THE WX IS -- THE NWS AND THE CTLRS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.