The impact of assimilating gps precipitable water vapor in convective-permitting wrf-arw on north american monsoon precipitation forecasts over northwest mexico

We assess the impact of GPS precipitable water vapor (GPS-PWV) data assimilation (DA) on short-range North American monsoon (NAM) precipitation forecasts, across 38 days with weak synoptic forcing, during theNAMGPS Hydrometeorological Network field campaign in 2017 over northwest Mexico. Utilizing an ensemble-based data assimilation technique, the GPS-PWV data retrieved from 18 observation sites are assimilated every hour for 12 h into a 30-member ensemble convective-permitting (2.5 km) Advanced Research version of the Weather Research and Forecasting (WRF-ARW) Model. As the assimilation of the GPS-PWV improves the initial condition of WRF by reducing the root-mean-square error and bias of PWV across 1200-1800 UTC, this also leads to an improvement in capturing nocturnal convection of mesoscale convective systems (MCSs; after 0300 UTC) and to an increase by 0.1mmh21 in subsequent precipitation during the 0300-0600 UTC period relative to no assimilation of the GPS-PWV(NODA) over the area with relatively more observation sites. This response is consistent with observed precipitation from the Integrated Multisatellite Retrievals for GPM Final Precipitation product. Moreover, compared to the NODA, we find that the GPS-PWVDAdecreases cloud-top temperature, increases most unstable convective available energy and surface dewpoint temperature, and thus creates a more favorable condition for convective organization in the region.