B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 142
Situational Awareness; Communication Breakdown
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Procedure; Weather; Human Factors
Due to GPS jamming in ZLC airspace and to the fact the airport was using a north flow instead of the south flow; Dispatch had planned and filed us for; and we received a pre-departure clearance that was amended to use a non-RNAV departure that worked with a north flow.  Our clearance read: ... BCE GRNPA1 KLAS.After departure; we needed to deviate around some thunderstorms in the area; and Center cleared us to do so direct MLF when able.  After checking in with Los Angeles Center; we were told; 'Cleared direct Milford; GRNPA 1 Arrival.'  Since our PDC included the GRNPA 1 already and it was already programmed into the FMC; we didn't realize MLF had its own transition on the GRNPA1.  After passing MLF and proceeding toward BCE; Center asked if we were on the arrival.  That's when we first realized the clearance had been different from what we had programmed and made the turn to KSINO to re-join the arrival.  There were no observed traffic conflicts due to our deviation.I should have referenced the STAR and queried ATC to clarify the clearance.  Also had ATC used the phrase 'cleared direct MILFORD; GRNPA 1; MILFORD transition' it would have alerted us to that the fact that the transition we were cleared to use had been changed.
B737-700 First Officer reports being cleared to LAS via BCE and the GRNPA1 arrival. Due to weather deviations the route is changed to direct to MLF and the GRNPA1. The crew does not notice that MLF is a transition on the GRNPA1 and turns to BCE after MLF. ATC intervenes.