*2.2. The WRF NWP System*

The modeling system used in the current work is WRF-ARW (advanced research WRF), version 4.0.2 [39], which is the core of the integrated HERMES modeling system that operates daily at NOA to support operational weather forecasting and natural disaster early warnings [40,41].

The WRF setup was based on two 2-way nested modeling domains, as shown in Figure 1a. The coarse domain (d01) was used to simulate the synoptic-scale atmospheric conditions with a spatial resolution of 10 km (mesh size of 500 × 500), while the innermost domain (d02) focused on the study area (Greece,) having a horizontal grid resolution of 2 km (mesh size of 551 × 551). The vertical structure of both domains included 41 unevenly spaced hybrid sigma-pressure layers up to 50 hPa. Initial and boundary conditions were obtained from the Global Forecast System (GFS) operational surface and upper air atmospheric analysis data at 0.25 × 0.25 spatial and 6 h temporal resolution, provided by the National Center for Environmental Prediction (NCEP). The selected physics parameterizations are presented in Table 2.

**Figure 1.** (**a**) The applied WRF domains' configuration and (**b**) study domain (d02) with the locations of the GNSS stations (blue dots; the red dot highlights the AUT1 station used for examining the NRT ZTDs' accuracy) and ground-based meteorological sites (yellow dots) utilized for the November 27 precipitation event, and with identification of regions where high rainfall amounts were observed during the examined episodes.


**Table 2.** Summary of the applied WRF model physics.

<sup>1</sup> Convection parameterization was used only for domain d01.
