A319 ENCOUNTERS MICROBURST ACTIVITY DURING APCH TO RWY 35R DEN; EXECUTES A GAR AND HAS AN EGPWS WINDSHEAR ALERT.

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INSIDE OM RWY 35L AT 6500 FT ON ILS; TSTM OVERHEAD AND SW OF FIELD. VIRGA OBSERVED; BUT NOT REACHING GND LEVEL. ACFT AHEAD RPTING LOSS OF 10 KTS ON SHORT FINAL. WE WERE GEAR DOWN FLAPS 3 DEGS WHEN TWR ISSUED A MICROBURST ALERT RWY 35R. NEXT ISSUED MICROBURST ALERT RWY 35L. WE WERE ISSUED GAR INSTRUCTIONS; CLB STRAIGHT AHEAD; MAINTAIN 7000 FT. TURNS AND OTHER ALTS NOT AVAILABLE DUE PARALLEL AND OVERHEAD TFC. INITIATED SOFT GAR. ACCELERATING AT 7000 FT AND FLAPS 2 DEGS; RECEIVED 'WINDSHEAR AHEAD' AURAL WARNING. ELECTED TO REMAIN AT FLAPS 2 DEGS AND 180 KTS RATHER THAN GET CAUGHT IN WINDSHEAR DURING FLAP RETRACTION. FLEW INTO STRONG UPDRAFT. COULD NOT MAINTAIN AIRSPD EVEN AT IDLE THRUST. RESULT WAS FLAP OVERSPD OF 10 KTS FOR APPROX 4 SECONDS. NO UNUSUAL VIBRATION NOTICED. FLAPS RETRACTED NORMALLY ONCE PAST THE UPDRAFT. THE ONLY WAY TO AVOID FLYING UNDER THE TSTM WOULD HAVE BEEN AN IMMEDIATE R TURN WHEN ISSUED MICROBURST ALERT; BUT THIS WAS NOT POSSIBLE DUE TO PARALLEL TFC ALSO GOING AROUND RWY HDG ON RWY 35R. HAD WE HAD ANY INDICATIONS OF THE IMPENDING MICROBURST WE WOULD NOT HAVE BEGUN THE APCH; BUT THE MICROBURST CAUGHT ALL ACFT ON APCH AND THE TWR BY SURPRISE. IN RETROSPECT; I OBVIOUSLY SHOULD HAVE ELECTED NOT TO START THE APCH. HOWEVER; I FELT THAT I HAD TAKEN ALL REASONABLE PRECAUTIONS GIVEN THE CIRCUMSTANCES. IN THE FUTURE; I WILL GIVE MORE CONSIDERATION TO OTHER TFC AND HOW IT MIGHT AFFECT MY GAR OPTIONS.