ACR X WX ENCOUNTER. NON ADHERENCE TO ATC CLRNC; TCASII RA. HAD LTSS FROM Y. PLTDEV.

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I WAS FO FOR THIS DC-9 ACR X FLT FROM ICT TO MEM AND WAS THE PF. WE WERE APCHING MEM AND DUE TO LINES OF TSTMS HAD TO DEVIATE N OF GQE ON THE ARR. APCH CTL TURNED US SE AND DIRECTED US TO INTERCEPT THE LOC FOR RWY 18R. THIS WAS OUR FIRST GOOD LOOK AT THE WX AFFECTING OUR APCH AND WAS LYING NNW THROUGH SSE. WE WERE 25 MI N OF MEM. A LINE HAD JUST GONE THROUGH MEM AND THE LINE WE WERE CONCERNED WITH WAS LOOKING TO BE 7-8 MI FROM THE ARPT AS WE TURNED S. WE PROCEEDED S AND WERE DSNDING WHEN APCH SWITCHED US TO RWY 18L. WE WERE ASKED TO MAINTAIN 6000 FT AT ABOUT 20 MI OUT. THERE WAS NO FURTHER COM FOR A FEW MI; SO I ASKED THE CAPT TO TELL THEM WE HAD TO HAVE LOWER SINCE WE WERE WELL ABOVE THE GS. WE NOW REALIZED THAT WE HAD TO GET LOWER BECAUSE THE WX WAS MOVING VERY FAST AND A GAR WOULD BE A DIFFICULTY. APCH CAME BACK TO ADVISE THAT THE TWR WAS CLOSED DUE TO HIGH WINDS AND HAD BEEN ABANDONED FOR THE TIME BEING. ARPT CLOSED. WE WERE TOLD TO TURN R TO 270 DEGS AND I COMPLIED IMMEDIATELY; SENSING WE WERE ABOUT TO BE TRAPPED IN A DEAD END AS THE WX WAS CLOSING IN IN FRONT OF US IN A WAY WE HAD NOT EXPECTED. AS WE BEGAN THE TURN IT WAS OBVIOUS TO US THAT WE HAD TO CONTINUE THE TURN OR FLY RIGHT INTO A LEVEL 4 OR 5 TSTM SO I DID SO WHILE THE CAPT TRIED TO COORD. COM WAS DIFFICULT DUE TO FREQ CONGESTION. ALTHOUGH WE WERE BANKING AT MAXIMUM WE COULD NOT CLR THE WX AND WE ENTERED THE EDGE OF THE TSTM; IMMEDIATELY ENCOUNTERING SEVERE TURB AND BEGAN TO LOSE ALT WITH THE ACFT ON AUTOPLT. THE TCASII SHOWED THE ACFT WHICH HAD BEEN FOLLOWING US AT 2 O'CLOCK AND MAYBE 2 MI AS WE SWUNG THROUGH 360 DEGS. WE HAD LOST ABOUT 600 FT AT THIS POINT AND STILL HAD TO COME BACK TO THE NE EVEN MORE TO EXIT THE TSTM AREA AND FIND THE CLR AIR WE HAD JUST LEFT. THE TCASII WAS EMITTING AN RA INITIALLY ADVISING TO 'MONITOR VERT SPD' AND THEN TO 'CLB; CLB NOW!' AS OUR SIT CHANGED. I DISCONNECTED THE AUTOPLT; INITIATED FULL PWR AND STARTED A CLB; PASSING WITHIN APPROX 1/2 MI AND 300-400 FT OF THE TARGET. TOTAL ELAPSED TIME FROM ENCOUNTERING THE TURB WAS NO MORE THEN 30 SECONDS. THIS WAS AN APCH WHICH PROBABLY SHOULD HAVE NEVER BEEN STARTED. HOWEVER; IT WAS SIMILAR TO MANY WHICH ARE COMPLETED ALL OF THE TIME WHEN WX OF THIS TYPE IS PRESENT. WE WERE UNAWARE OF THE SPD AT WHICH IT WAS MOVING OR THAT IT HAD SPAWNED A TORNADO IN MEM JUST 30 MIN PRIOR TO OUR ARR IN THE AREA. WE GOT TRAPPED IN AN ALLEY WHICH CLOSED IN ON US MAKING ESCAPE VERY DIFFICULT.