Precipitable water vapor from Sentinel-1 improves the forecast of extratropical storm Barbara

High-resolution water vapor fields retrieved over Iberia during the passage of storm Barbara (October 19–20, 2020) by Sentinel-1 and assimilated by the Weanther Research & Forecasting Model (WRF) reveal a substantial positive impact on water vapor forecasting. Due to the path followed by the storm across Iberia, from its southwestern to the northeastern corners, and the geometry of Sentinel-1 data acquisition, it is possible to show, for the first time, the potential added value of precipitable water vapor (PWV) obtained by the Interferometric Synthetic-Aperture Radar (InSAR) technique, as a data source for both the forecast and validation of meteorological forecasts of synoptic-scale storms. Results indicate that data assimilated in the InSARfootprint positively impact the downstream forecasts up to the northeastern boundary, about 850km and 12 hours away, with improved skill scores of the water vapor distribution and improved forecasts of rain.