INBND TO DEST WITH INSUFFICIENT FUEL TO HOLD FOR WX; FLT CREW OF A319 DIVERTS TO A NEARBY ARPT. DECLARE LOW FUEL EMER. CONDITION CAUSED IN PART BY ACR FUEL POLICY LIMITING UNILATERAL ADDITION OF FUEL BY FLT CREW AND THE INABILITY TO COM WITH THE DISPATCHER PRIOR TO DEP.

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UPON GATHERING THE PAPERWORK FOR OUR FINAL DAY'S LEG; IT WAS NOTED THAT OUR FUEL WAS 3.5 RESERVE AND 1.2 EXTRA. WX IN ZZZ1 WAS FORECAST TO BE SCATTERED CLOUDS WITH VERY ISOLATED CUMULONIMBUS. I ATTEMPTED TO CONTACT THE DISPATCHER 3 TIMES; BUT NOBODY ANSWERED THE PHONE. I ADDED MY CAPT'S ALLOWABLE 500 LBS OF FUEL. I WAS AWARE THAT A DRYING TREND FOR THE AREA WAS SUPPOSED TO OCCUR AND FIGURED THAT IT MUST BE OCCURRING OR THE DISPATCHER WOULD LIKELY HAVE BEEN MORE APT TO GIVE ME MORE FUEL. AS WE APCHED ZZZ1 AND WERE ABOUT READY TO BEGIN OUR INITIAL DSCNT; I TOLD THE FO TO GET THE WX; SINCE IT LOOKED QUITE OMINOUS OVER ZZZ1. INDEED ZZZ1 WAS INUNDATED WITH TSTMS; WINDSHEAR AND MICROBURST WARNINGS. WE WOULD BE ABLE TO MAKE ZZZ2 WITH 4.0 FUEL IF WE WENT DIRECT NOW! WE MADE OUR REQUEST AND WERE GIVEN VECTORS IN THE GENERAL DIRECTION OF ZZZ2 FOR OTHER SMALLER LINES OF WX THAT WERE FORMING. SOME SCATTERED TSTMS WERE BEGINNING TO MOVE TOWARD ZZZ2. I DECLARED A LOW FUEL EMER AND REQUESTED DIRECT. ATC WAS VERY HELPFUL; WE SQUARED AWAY WITH ATC THAT IT WAS INDEED FOR LOW FUEL AND NO EQUIPMENT WOULD BE NECESSARY. LNDG WAS MADE SAFELY IN ZZZ2 WITH 4.0 FUEL REMAINING. WE PROBABLY COULD HAVE MADE ZZZ3; BUT AS USUAL; THE SYSTEM EVEN WITH ACARS DOESN'T ALLOW QUICK CONTACT WITH OUR DISPATCHER SINCE HE WAS ALSO BUSY WITH OTHER ACFT HAVING SIMILAR DIFFICULTIES.