LGT DEVIATES WX DOES NOT NOTIFY ATC.

Narrative

THERE WAS A WIDESPREAD AREA OF TSTM ACTIVITY W OF ORD WHICH RESULTED IN GND HOLDS AND LIMITED OPS IN THAT DIRECTION. WE WERE FINALLY CLRED FOR TKOF AND AS WE CLBED OUT; WE WERE GIVEN APPROVAL TO DEVIATE AROUND WX A FEW TIMES. AS WE PASSED FL190; WE WERE ASSIGNED A 270 DEG HDG AND HANDED OFF TO ANOTHER CTLR. AT THAT TIME; THERE WAS A SMALL CELL AT OUR 12 O'CLOCK POS AND ABOUT 20 MI OUT. THE CELL WAS GROWING WITH EACH SWEEP OF THE RADAR; SO WHEN I CHKED IN; I TOLD THE CTLR WE WOULD HAVE TO DEVIATE EITHER L OR R FOR WX. HE RESPONDED BY CLRING US TO FL310 AND TOLD US WE COULD TURN R AND PROCEED DIRECT ALO WHEN WE PASSED FL240. OUR CLB RATE WAS LESS THAN 1000 FPM DUE TO THAT ACFT'S SMALL ENGS; AS WELL AS THE USE OF ENG HEAT. THE 270 DEG HDG WAS POINTING US AT THE MIDDLE OF THE CELL AND AFTER ABOUT 2 MINS; IT BECAME APPARENT THAT WE WERE NOT GOING TO REACH FL240 IN TIME TO DEVIATE AROUND THE WX WITH A R TURN. IN ORDER TO AVOID PENETRATING THE HIGHEST DENSITY RADAR RETURN; I DIRECTED THE FO TO TURN 10 DEG L TO A 260 DEG HDG. I THEN CALLED THE CABIN CREW ON THE INTERPHONE TO ADVISE THEM OF THE PROBABLE TURB AND MAKE SURE THEY WOULD TAKE THEIR SEATS AND STRAP IN. ABOUT THE TIME WE PASSED ABEAM THE CELL; THE CTLR CALLED AND ASKED FOR OUR HDG. AFTER I REPLIED; HE TOLD US WE HAD TFC TO THE S AND THEN ASSIGNED A 290 DEG HDG; WHICH WE TURNED TO IMMEDIATELY. THE CTLR THEN PROCEEDED TO GIVE ME A RATHER HARSH SCOLDING. I GOT THE FEELING THAT HE DIDN'T REALLY CARE IF WE HAD TO FLY THROUGH A TSTM -- HE JUST NEEDED TO MAINTAIN HIS SEPARATION. I DON'T THINK WE WERE ON THE 260 DEG HDG FOR MORE THAN 2 MINS; BUT I GUESS THE ATC SYS HAS BECOME SO SATURATED IN PLACES LIKE ORD; THERE IS LITTLE OR NO ROOM FOR ERROR. THIS MAKES IT HARD FOR EVERYONE -- ESPECIALLY DURING IRREGULAR OPERATING CONDITIONS.