INACCURATE WX RPTING BY ASOS.

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I AM EXTREMELY CONCERNED ABOUT THE ACCURACY AND RELIABILITY OF THE NEWLY INSTALLED ASOS AT THE JACKSON INTL ARPT. IN RECENT MONTHS THE ASOS SYS ROUTINELY RPTS VALUES THAT DO NOT REFLECT THE ACTUAL WX CONDITIONS PREVAILING AT THE TIME. IN ADDITION; THE ASOS SYS CONSISTENTLY LAGS BEHIND IN RPTING SIGNIFICANT CHANGES IN THE WX OCCURRING AT THE ARPT. I FEEL THAT THE INADEQUACIES OF THIS SYS RESULT IN AN UNACCEPTABLE MEANS OF DETERMINING THE WX CONDITIONS AT THE JAN ARPT. MY GREATEST CONCERN IS THE POTENTIAL FOR A PLT TO HAVE GROSSLY INACCURATE WX RPTS DURING THE LNDG PHASE OF THE FLT. A 10-15 MIN DELAY IN RECEIVING CORRECT WX IS NOT COMPATIBLE WITH AVIATION SAFETY. THIS UNACCEPTABLE CONDITION IS PARTICULARLY TROUBLING WHEN COUPLED WITH THE FACT THAT PLTS ARE EXECUTING CATII AND CATIII INST APCHS AT JAN. IT IS ABSOLUTELY IMPERATIVE THAT PLTS HAVE TIMELY; ACCURATE WX INFO DURING THESE OPS. I MUST RPT THAT THE NWS AT JAN ARPT HAS BEEN COMPLETELY UNRESPONSIVE WHEN INFORMED THAT THE ASOS IS RPTING ERRONEOUS INFO. IT WAS MY UNDERSTANDING WHEN THE ASOS WAS INSTALLED THAT IF ERRONEOUS INFO WAS SUSPECTED A MANUAL OBSERVATION WOULD BE PERFORMED. THE WX SVC HAS BEEN VERY RESISTANT TO MAKING MANUAL OBSERVATIONS AND IN MOST CASES HAS BEEN UNWILLING TO RESPOND TO OUR REQUESTS. WX SVC PERSONNEL SEEM TO IGNORE OUR REQUESTS EVEN WHEN WE MAKE IT CLR THAT THE ASOS INACCURACIES ARE ADVERSELY AFFECTING AVIATION OPS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED ASOS WILL NOT UPDATE CURRENT WX CONDITIONS AT THE ARPT DURING RAPIDLY CHANGING WX. WHEN REQUESTED TO TAKE A SPECIAL OBSERVATIONS; NWS PERSONNEL SAY IF THERE IS NO MAJOR CHANGE TO WX THEY WILL NOT AUGMENT THE SYS. RPTR HAS BEEN TOLD THIS IS POLICY SET DOWN BY NWS IN WASHINGTON HEADQUARTERS.