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The North American monsoon (NAM) is responsible for summer severe weather in the Southwest U.S. and northwest Mexico and its associated rainfall contributes the highest percentage of yearly precipitation to this region. Short-term convection-allowing model forecasts have shown difficultly in replicating the diurnal cycle of NAM convective precipitation. Generally, convection initiating over the Sierra Madre Occidental (SMO) mountain range in the early afternoon may later organize into mesoscale convective systems (MCSs) that propagate west towards the lower elevations and Gulf of California (GOC). MCSs account for the greatest proportion of all NAM-related precipitation. In my dissertation, I investigate the performance of daily short-term WRF hindcasts on moisture and precipitation with and without the assimilation of precipitable water vapor (PWV) measurements from Global Positioning System (GPS) ground receivers in the NAM GPS Transect Experiment 2013. In Chapter 2.1, I investigate the overall performance of daily hindcasts during the 2013 monsoon season without data assimilation. The 2.5-km convection-allowing hindcasts consistently display a moist bias in their initial conditions compared to GPS-PWV observations; this leads to diurnal convection beginning 3-6 hours earlier than observations. Because the precipitation forecast skill varies with the proximity of an inverted trough (IV), I compare the days when an IV is present (“strongly forced”) to days when an IV is not present (“weakly forced”). I find that strongly forced days display higher precipitation forecast skill than weakly forced days especially in the slopes of the northern SMO west of the crest that is associated with MCSs. In a case study spanning 8-9 July 2013, when nearly identical MCSs evolved over northern Sonora on consecutive days, the MCS is poorly simulated on the first day (weakly forced) when the IV is east of the SMO while a salient MCS is simulated on the second day (strongly forced) w