TEMPORARY LOSS OF ACFT CTL AND AIRSPD DEVS ARE EXPERIENCED BY LGT ACR FLC IN DEP PROC FROM ARPT SURROUNDED BY TSTM ACTIVITY.

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AFTER ABOUT A 3 HR 40 MIN DELAY ON THE GND (DUE TO A CONTINUOUS SERIES OF TSTMS) OUR FLT WAS CLRED FOR TKOF ON RWY 24R. AFTER WE TAXIED INTO POS; WE NOTICED ON RADAR A SOLID LINE OF CUMULO NIMBUS BEGINNING DIRECTLY OVERHEAD AND EXTENDING ROUGHLY 60 MI OFF THE DEP END OF RWY 24R. MODERATE WITH OCCASIONAL HVY RAIN WAS FALLING ON THE ARPT AND THE WIND SOCK INDICATED FREQUENT CHANGES IN BOTH DIRECTION AND VELOCITY OF WIND. AFTER ABOUT A MIN OR 2 OF FLT TIME WE TOLD DEP CTL WE NEEDED A L TURN FOLLOWED BY FREQUENT DEVS TO AVOID STRONG CELLS. THE CAPT WAS FLYING AND WE WERE BOTH OPERATING THE RADAR AND MAKING FREQUENT VISUAL REFS OUTSIDE. DURING THE COURSE OF WX AVOIDANCE; WE ENCOUNTERED 2 EPISODES OF STRONG DOWNDRAFTS. THE FIRST DOWNDRAFT (OR WIND SHEAR) WAS OF SIGNIFICANT DURATION -- APPROX 10 SECONDS. THE SINKING SENSATION IMMEDIATELY GOT OUR ATTN AND WE BOTH MUST HAVE BEEN LOOKING OUTSIDE TO SEE WHAT WE WERE ENCOUNTERING. UPON SCANNING BACK IN AT THE RADAR AND FLT INSTS; I NOTICED OUR AIRSPD WAS APCHING 300 KTS (AT APPROX 6000 FT). IMMEDIATELY WE NOTICED AN UPDRAFT FOLLOWED BY ANOTHER DOWNDRAFT. IT WAS AT THIS TIME THAT CTR QUERIED US ABOUT OUR AIRSPD. IN THE NEXT FEW SECONDS; I KEYED THE MICROPHONE 2 TIMES TO MAKE A RESPONSE BUT WAS INTERRUPTED BOTH TIMES BY THE CAPT WHO WAS TELLING ME WHAT EXPLANATION HE WANTED MADE. I GUESS WHEN THE CTLR HEARD THE KEYING OF THE MICROPHONE AND NO XMISSION MADE; HE MUST HAVE THOUGHT WE DIDN'T KNOW HOW TO RESPOND. SO HE SAID; 'NEVER MIND; I DON'T WANT TO KNOW! JUST GET IT BACK TO 250 KTS!' THE CAPT WENT AHEAD AND MADE THE EXPLANATION AND REQUESTED FURTHER DEVS BECAUSE A SLOWING OF AIRSPD WOULD HAVE REQUIRED AN INORDINATELY HIGH PITCH ATTITUDE AND WOULD HAVE PLACED US SQUARELY IN THE MIDDLE OF A STRONG CELL. AFTER DEVS WERE GRANTED; WE ACHIEVED BETTER SEPARATION FROM THE WX AND WERE ABLE TO REGAIN CTL OVER AIRSPD. THE REMAINDER OF THE CLB AND FLT WERE NORMAL. LOOKING BACK ON IT; I SUPPOSE ONE COULD SAY THAT ONE PLT SHOULD BE MONITORING FLT INSTS AT ALL TIMES SO THAT IF A DEV OCCURS; HE CAN ADVISE THE PF IMMEDIATELY. BUT IN THE CASE OF SEVERE WX AVOIDANCE; A COMBINATION OF RADAR OP AND OUTSIDE VISUAL REF SOMETIMES REQUIRES THE EFFORTS OF BOTH PLTS IN ORDER TO INSURE SAFETY OF FLT. WE APPRECIATE THE APPARENT UNDERSTANDING OF ATC IN THIS INSTANCE.