SyWeDaG is an open-source desktop application for generating multivariable synthetic weather time series at hourly resolution from historical daily observations and monthly climate projections. The software addresses the mismatch between aggregated climate products and the fine-resolution inputs required by engineering and environmental simulations, a gap that constrains fields such as renewable-energy assessment, building-energy modelling, urban demand studies or maintenance planning. It integrates historical-data acquisition, local persistence, climate conditioning, multivariable correction, temporal disaggregation, validation, visualization, and export in a single workflow. Historical observations can currently be retrieved from AEMET and Open-Meteo through a common provider interface. Synthetic daily series are constructed by resampling complete historical years and, when projections are supplied, adjusting temperature and precipitation to monthly targets. Humidity, pressure, and wind are then corrected using either nearest-neighbour transfer or XGBoost regression. Variable-specific algorithms transform daily records into continuous hourly profiles while checking consistency across monthly, daily, and hourly scales. A Streamlit interface enables users without specialist programming knowledge to select locations, configure scenarios, inspect results, and export reproducible packages containing data and provenance metadata. The implementation is intended for scenario exploration rather than operational forecasting, and its modular architecture supports the addition of data providers, climatic variables, correction models, and alternative disaggregation procedures.