Impact of Total Column Water Vapor Measurements on Short- to Medium- Range Forecasts of North American Monsoon Precipitation

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The objective of this research is to evaluate the ability of observations of total column precipitable water (TPW) from ground-based Global Positioning System (GPS) receivers to improve forecasts of precipitation occurring as part of the North American Monsoon (NAM). The NAM begins in southern Mexico in May and expands north and westward along the Sierra Madre Occidental, reaching the US Southwest in late July and early August. The bulk of NAM precipitation comes from mesoscale meteorological processes, including squall lines and mesoscale convective complexes, and thus successful numerical weather prediction requires the use of a high-resolution nonhydrostatic weather forecasting model. In addition, previous work suggests that successful prediction of NAM precipitation must include observations from the regions of convective initiation, and adequately represent low-level surges of moisture into the NAM region. Thus, this project examines the ability of the Advanced Research Weather Research and Forecasting model (WRF ARW), integrated using a nonhydrostatic high resolution inner domain, to produce skillful NAM precipitation forecasts using continuous TPW observations from a network of GPS ground stations in the US (Suominet) and in Mexico (TLALOC-Net, a 100-station network currently under construction), with further experiments incorporating observations from the more distant COCONet network in the Caribbean. GPS receivers detect TPW as a consequence of the delay in GPS signal propagation from the transmitter satellite to the ground-based receiver due to the presence of atmospheric water vapor. In addition to these fixed networks, the PIs will work with colleagues at the National Autonomous University of Mexico on a field campaign in which 10 GPS receivers will be deployed in Northern Mexico (in the region of convective initiation) over the 2013 NAM season.In addition to its scientific merit, the work has broader societal impacts due to the importance of the NAM, which accounts for approximately 50-70% of the annual precipitation in northwest Mexico and the Southwest US. The NAM impacts water supply and demand, severe weather, extreme heat, drought and wildfire during the warm season. In addition, the work will foster collaborations between US and Mexican scientists in a research area of interest to both countries, and the work will support and train a graduate student.