A DISPATCHER REPORTS THE AUTOMATIC METAR REPORTING SYSTEM FAILED TO ALERT ABOUT A WX CHANGE REQUIRING AN ALTERNATE ARPT. THE FLT DEPARTED WITH NO ALT.

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FLT X PIC CALLED TO SAY ZZZ REQUIRED AN ALTERNATE. THERE WAS NO NOTICE OF ANY CHANGE IN THE FORECAST FOR ZZZ. ITS FORECAST CHANGED AT XA28Z. THE FLT WAS RELEASED WITH ZZZ1 AS THE ALTERNATE. NO DISPATCH DELAY AND NO EXTRA FUEL WAS REQUIRED. THE ACARS MESSENGER APPLICATION IS THE TOOL THAT DISPATCH RELIES UPON FOR NOTIFICATION OF CHANGES IN THE WX. IT IS AN AUTOMATED PROCESS. THOSE CHANGES INCLUDE WX FORECAST UPDATES; SPECIES; AND NOTAMS. TONIGHT; THE COMPUTER SYS THAT SENDS WX UPDATES TO THE ACARS MESSENGER WAS OFF LINE NUMEROUS TIMES DURING MY SHIFT. DURING ONE SUCH OUTAGE THE WX HAD CHANGED IN ZZZ. IN PARTICULAR A NEW FORECAST HAD BEEN ISSUED. WHENEVER; A NEW FORECAST IS ISSUED OR IF A FORECAST IS AMENDED IT WILL APPEAR IN THE ACARS MESSENGER AS 'UPDATE NOTICE XX.SPL.' SELECTING THIS FILE NAME WILL DISPLAY THE FOLLOWING AS AN EXAMPLE; 'DISPATCHER NOTICE -- XA:20:46; FORECASTS UPDATED FOR THE FOLLOWING STATIONS: ZZZ.' THERE WAS NO SUCH NOTICE OR ENTRY FOR ZZZ. ITS FORECAST CHANGED AT XA28Z. THE ORIGINAL FORECAST DID NOT REQUIRE ANY ALTERNATE. THE ACARS MISSED THE METER ISSUED AT XA15Z. THIS IS 13 MINS BEFORE THE FORECAST FOR ZZZ WAS UPDATED. IN SUMMARY THE COMPUTER THAT PROVIDES TIMELY AND CURRENT WX IS UNRELIABLE. IT IS OFTEN OFFLINE. WHEN IT IS OFFLINE NO CHANGES TO ANY OF THE WX PRODUCTS ARE STORED. WITHOUT A WAY TO STORE THIS INFO A DISPATCHER WILL NOT KNOW WHEN A DEST'S; ALTERNATE'S; OR ARPT'S WX WILL JEOPARDIZE THE SAFETY OF A FLT.