FLC OF AN MDT DEPARTED PRIOR TO ATC RELEASE DUE TO BEING DISTRACTED BY WORSENING TERMINAL WX CONDITIONS.

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WHILE TAXIING TO RWY 13 AT INL; MY FO REQUESTED AND GOT AN IFR CLRNC TO MSP. THE CTLR ASKED IF WE WERE 'READY TO GO.' MY FO SAID 'NOT QUITE YET.' (WE HAD TO FINISH TAXIING TO THE END OF RWY 13 AND NEEDED TO COMPLETE OUR 'BEFORE TKOF' CHKLIST.) THE MSP CTLR RESPONDED BY GIVING US A 'HOLD FOR RELEASE' CLRNC; AND REQUESTED WE CONTACT HIM WHEN WE WERE READY TO GO. FOR THIS SERIES OF FLTS WE WERE OPERATING A SAAB 340A; AND HAD A L BLEED DEFERRED WHICH NECESSITATED OUR FLYING IN VFR CONDITIONS WITH 'NO FLT INTO KNOWN OR FORECAST ICING.' ALTHOUGH THE MOST RECENT WX SEQUENCE AT XA50Z WAS 16 SCATTERED; 130 OVCST 15; 260/23/11 0000/022; WE NOTICED THAT THERE WERE BROKEN CLOUDS MOVING INTO THE AREA FROM THE WESTERLY SIDE OF THE ARPT. WE WERE CONCERNED THAT WE WOULD NOT BE ABLE TO DEPART IF THESE BROKEN LAYERS OF CLOUDS MOVED IN (DUE TO OUR MEL'D L BLEED VALVE CONDITION). SO; IN OUR HASTE WE DEPARTED IN VFR CONDITIONS AND CONTACTED ATC WHEN AIRBORNE. BOTH MY FO AND MYSELF FORGOT ABOUT OUR 'HOLD FOR RELEASE' CLRNC; AS WE WERE CONCENTRATING ON THE WX SIT. ATC IMMEDIATELY QUESTIONED WHY WE HAD DEPARTED WITH A 'HOLD FOR RELEASE CLRNC;' AND LATER WE WERE TOLD TO CONTACT A SUPVR AT THE MSP ATC QUALITY ASSURANCE DEPT. HE SAID A RPT OF THIS ATC DEV WAS BEING SENT TO MSP FSDO.