AN EMB-135 FLT CREW ENCOUNTERED WINDSHEAR ON APPROACH TO STL WITH SIGNIFICANT AIRSPEED FLUCTUATIONS. THEY EXECUTED A MISSED APPROACH AND DIVERTED TO THEIR ALTERNATE.

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I WAS THE PNF ON FLT FROM ZZZ TO STL ON SEP/XA/08. BEFORE I LEFT THE HOTEL I CONTACTED DISPATCH TO TALK ABOUT THE WX IN STL WHERE IT WAS RECEIVING THE AFTERMATH OF A HURRICANE. THE CURRENT WX WAS 1 SM; 1200 FT OVCST; AND WINDS 010 DEGS AT 25 KTS GUSTING 35 KTS. THE FORECASTED WX WAS REAL SIMILAR AND SEEMED TO HOLD TRUE. ON ILS RWY 30R APCH INTO STL AROUND 1500 FT I NOTICED OUR AIRSPD RAPIDLY DECREASING AND YELLED PWR. ALMOST SIMULTANEOUSLY THE FO ADDED PWR AND WE RECEIVED A RED WINDSHEAR WARNING. THE FO THEN EXECUTED THE WINDSHEAR PROCS BY ADDING MAX THRUST AND PRESSING THE GAR BUTTON. I INFORMED THE TWR THAT WE WERE GOING MISSED DUE TO WINDSHEAR. THEIR INSTRUCTIONS WERE CLB AND MAINTAIN 3000 FT. AFTER THE WINDSHEAR WARNING WENT AWAY WE CLEANED UP THE ACFT. RAPIDLY APCHING 3000 FT I NOTICED THE FO HAD TO USE AN EXCESSIVE FORWARD FORCE ON THE CTL COLUMN TO DECREASE THE RATE OF CLB. I COULD TELL WE WEREN'T GOING TO LEVEL OFF. I TOLD HIM TO PRESS AND HOLD THE QUICK DISCONNECT BUTTON BECAUSE I THOUGHT WE MAY HAVE A RUNAWAY TRIM BECAUSE OF THE AMOUNT OF FORWARD FORCE TO SLOW DOWN THE CLB. I INFORMED ATC THAT WE NEED HIGHER AND THEY GAVE US 4000 FT THEN 5000 FT AND THEN A BLOCK ALT THAT WE REQUESTED FROM 5000 FT TO 8000 FT. OUR RATE OF CLB WITH FULL NOSE FORWARD PRESSURE ON THE CTL WAS AROUND 500-1000 FPM. THIS WAS ALSO WITH A DECREASED AMOUNT OF PWR THAT KEPT US ANYWHERE FROM 200 KTS TO 220 KTS; AS AIRSPD WAS ALSO HARD TO CTL DUE TO TURB. I CONTINUED TO RUN THE QRH AND CUTOUT BOTH PITCH TRIM SYS. THEN I TURNED THE MAIN SYS BACK ON AND THE FO WAS THEN ABLE TO USE THE TRIM. WE STABILIZED THE ACFT AT 7000 FT. DURING THIS EVENT I AM UNSURE IF WE DEVIATED FROM ANY ASSIGNED ALT BECAUSE WE WERE IN CONSTANT COM WITH THE ATC AND WERE RECEIVING HIGHER ALTS; FOLLOWED BY A REQUESTED BLOCK ALT. IN OUR CLB I INFORMED ATC OUR INTENTIONS WERE TO DIVERT TO ZZZ1; OUR ALTERNATE; WHERE THE WX WAS BETTER. I THOUGHT THIS WAS THE BEST DECISION DUE TO CURRENT STATE CONDITIONS. WE PROCEEDED TO ZZZ1 AND COMMUNICATED WITH DISPATCH ON RADIO AND ON THE GND.