MD80 FLT CREW INADVERTENTLY CROSS THE RWY 17R HOLD LINE AT DFW IN HVY RAIN CONDITIONS.

Narrative

DUE TO HVY RAIN AND LIGHTNING; GATE DEP WAS DELAYED 34 MINS (RAMP CLOSED). WHEN PWRBACK REQUESTED; WE WERE CLRED TO PWRBACK; TAXI; L TURN; EXIT SPOT XX. AFTER PWRBACK AND STILL ON THE RAMP YELLOW LINE; GND STARTED ASKING; SPOT XX. THE FO ACKNOWLEDGED AND WE WERE CLRED STANDARD TAXI RWY 17R. DUE TO THE HVY RAIN AND SEVERE LCL TSTMS; I TURNED ON THE RADAR EXITING THE RAMP IN ORDER TO CHK THE WX TO THE E AND N. I MISSED TXWY L THINKING IT TO BE TXWY K AND PASSED THE HOLD SHORT LINE FOR RWY 17R AT TXWY EJ BY ABOUT 5-10 FT. I IMMEDIATELY REALIZED MY ERROR AND STOPPED SHORT OF THE ACTUAL RWY EDGE BY ABOUT 40 FT. SIMULTANEOUSLY; GND CTL STATED 'YOU ARE ON THE RWY; CONTACT TWR.' TWR STATED THERE WAS NO CONFLICT OR PROBS AND WE WERE CLRED ONTO THE RWY TO BACK-TAXI TO THE END. PROBABLE CAUSES: 1) RUSHING BY BOTH RAMP AND GND CTLRS DURING RAMP TAXI. 2) HVY RAIN; REDUCED VISIBILITY AND TXWY CONSTRUCTION. 3) PLT OVERCONCERN ABOUT SEVERE WX AND SUBSEQUENT INATTN TO ACFT POS AND MOVEMENT DURING TAXI WHILE CHKING RADAR FOR POSSIBLE DEP DEVS.