AN ACR MLG ACFT ON DEP HEADING VECTOR AND SID HAD TO DEVIATE DUE TO SEVERE WX AHEAD. FLC ATTEMPTED TO CONTACT DEP CTLR TO REQUEST DEV; BUT FREQ WAS IN CONSTANT USE AND FLC COULDN'T COMMUNICATE WITH THE CTLR SO THEY HAD TO DEVIATE WITHOUT PRIOR CLRNC; EXERCISING CAPT EMER AUTH.

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BTWN THE PROVERBIAL ROCK AND A HARD PLACE. THE 'ROCK' IN THIS CASE WAS CONFLICTING TFC; THE 'HARD PLACE' WAS TSTM CELLS. WE WERE ON A FLT FROM SAT TO ORD. THE INFO WE FLT PLANNED WITH SHOWED SIGMETS FOR EMBEDDED TSTMS IN THE AREA AND PIREPS OF MODERATE MIXED ICE. ON THE DEP WE WERE GIVEN A HEADING TO INTERCEPT THE SID RADIAL AND AN ALT CLRNC OF 13000 FT. 2 TSTM CELLS POPPED UP ON THE RADAR SCREEN. OUR COMPANY POLICY IS TO AVOID THIS KIND OF CELL BY 5 NM OR MORE. THE DEP CTLR WAS TALKING NON STOP TO OTHER AIRPLANES PREVENTING US FROM EITHER REQUESTING A WX DEV TURN OR DECLARING AN EMER IF NECESSARY. I HAD THE CHOICE OF EITHER ENTERING THE CELL AND POSSIBLY HAVING THE AIRPLANE TORN APART; OR TURNING TO AVOID THE CELL (BY MAYBE 1 NM BY NOW) AND HOPING THAT TCASII AND/OR THE RADAR CTLR WOULD WARN US OF OTHER TFC. I CHOSE THE LATTER. I DIDN'T SEE ANY TCASII TFC DISPLAYED AND TURNED R. MY FO WAS FINALLY ABLE TO ADVISE THE CTLR. WE WERE TOLD TO LEVEL AT 12000 FT (DUE TO SAME DIRECTION PARALLEL TFC AT 13000 FT); AND WERE REPRIMANDED FOR NOT GETTING PERMISSION BEFORE TURNING. UNLESS I AM MISTAKEN; WE FOLLOWED FAR GUIDANCE: ASK PERMISSION; DECLARE AN EMER IF NECESSARY; IF UNABLE OTHERWISE; FOR SAFETY OF FLT DEVIATE AND NOTIFY ATC ASAP. PERHAPS ROUTINE 'PROGRESS' COM FROM CTLRS AS TO WHERE WE HAVE TFC NEARBY WHEN ACFT ARE KNOWN TO BE IN IMC WOULD HELP IN THESE SITS.