ACFT UNCONTROLLABLE IN SEVERE WX DUE TO UNFORECAST SEVERE TURBULENCE.

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BEFORE MY DEP I HAD RECEIVED SEVERAL WX BRIEFINGS FROM ORL FSS. THE FINAL ONE INDICATED VFR CONDITIONS; POSSIBILITY OF IFR CONDITION; NO FLT PRECAUTIONS OR CONVECTIVE ACTIVITY ENRTE. THIS WAS 10 MINS BEFORE TKOF. I DEPARTED IN VFR CONDITIONS FROM LEE AND PICKED UP MY IFR CLRNC FROM ORL APCH. ABOUT 30 MI OUT OF LEE I WAS SWITCHED TO TPA APCH AND STARTED ENTERING IMC. THEN TPA APCH ADVISED PIE WX 300 OVCST 1 1/2 MI FOG AND TO EXPECT THE ILS 17L AT PIE. THEN TPA APCH ADVISED NOW TO EXPECT THE BC 35R AND TO TURN RIGHT TO A MORE WESTERLY HDG AND TO CLB TO 2600' FROM 2000'. I INITIATED THE TURN AND THE CLB; BUT BEFORE I WAS ABLE TO COMPLETE THE CLB WE ENTERED AN AREA OF SEVERE TO EXTREME TURB WHICH RESULTED IN A TEMPORARY LOSS OF CTL. THE AIRSPD; ALT AND ATTITUDE FLUCTUATED WILDLY (AIRSPD +/- 70 KTS AND RATE OF CLB +/- 2000 FPM). I IMMEDIATELY CONTACTED TPA APCH RPTING THAT WE WERE ENCOUNTERING SEVERE TURB AND WERE UNABLE TO MAINTAIN ANY ALT AND REQUESTING AN IMMEDIATE VECTOR TOWARD AN AREA OF CLR WX. THE CTLR ONLY RESPONDED WITH ALT ALERTS AND INSTRUCTED ME TO CLB AND MAINTAIN MY ASSIGNED ALT. THE RADAR; WHICH BEFORE ONLY INDICATED LIGHT PRECIPITATION WAS USELESS DUE TO THE EXTREME ATTITUDE CHANGES. I WAS FINALLY ABLE TO REGAIN CTL AT 500' MSL AND THE CTLR FINALLY SUGGESTED AN ARPT AT OUR 12 O'CLOCK AND 3 MI; AT WHICH I MADE AN EMER LNDG. I FEEL THAT THE GREATEST FACTOR IN THIS CASE WAS THAT THE CTLR UNKNOWINGLY VECTORED ME INTO AN AREA OF SEVERE TURB AND I THINK THIS INCIDENT AND MANY OTHERS COULD BE AVOIDED IF ATC FACS WOULD HAVE ADEQUATE WX DETECTION AND AVOIDANCE EQUIPMENT SUCH AS DOPPLER RADAR TO SUPPLEMENT THE WX INFO THE PLT OBTAINS BEFORE FLT WITH IN FLT UPDATES AND ASSISTANCE. ALSO; THE ROUTE I WAS FLYING HAD NO WX RPTING FACS ENRTE. IN SUCH AREAS THE FAA SHOULD PLACE AUTOMATED WX RPTING FACS AND ATC SHOULD SOLICIT PIREPS FROM PLTS IN ADVERSE WX SITUATIONS AND DISSEMINATE THEM ASAP IN THE CASE OF URGENT PIREPS DIRECTLY OVER ATC COM FREQ JUST LIKE SIGMETS.