The NWS plume forecasts at TUS for PW are shown above - PW jumps from around 0.25" to more than 0.50" (some members forecast values approaching 1.00") on Thursday and Friday. However, the plumes for QPF (below) are not very impressive at all for TUS - one member is out-of-sync with others and forecasts about 0.70" at the airport.
The AR Portal forecasts of the probability of Integrated Vapor Transport (IVT) greater than 250 kg/m/s are shown here. Forecast above is valid at 00 UTC on Wednesdayand indicates a fairly broad plume of moisture from just east of Hawaii into northern California. By 00 UTC on Friday the ensemble members have forecast a broadening, as well as a break off from the Hawaiian plume, and have high probabilities for important IVT over most of western US, including much of Arizona.
Bottom line this far out seems to be high confidence for much increased PW by end of week, but much less confidence (at least here in southern Arizona) in what this will mean for precipitation.
A portion of the FD from PHX issued early yesterday am is shown down at the bottom.