In the thesis the comparison between temperature and relative humidity from ERA5 reanalysis with actual values obtained from radiosonde measurements was analysed. The analysis was conducted at 37 vertical levels for the Zagreb and Zadar regions throughout the year, as well as for the winter and summer seasons, considering data at midnight, noon, and their averages. Mean values and standard deviations were compared for the selected period, with accompanying t-tests for mean values and F-tests for standard deviations at a significance level of 5%. A strong match was found for the mean temperature values, while ERA5 exceeded the relative humidity for almost all vertical levels due to its lower predictability. When changing location, season, or time of day, the results showed that only the season noticeably affected the values and the relationship between curves. Anomalies of temperature, relative humidity, and specific humidity were calculated and graphically represented for the entire available ERA5 period, demonstrating tropospheric warming, stratospheric cooling, and an increase in specific humidity in the last decade. Transitioning from the entire year to selected seasons intensified positive and negative anomalies. Trends in temperature, relative humidity, and specific humidity for ERA5 data were also analyzed, presented with values per decade along with corresponding t-tests. Significant trends were observed for temperature and specific humidity for almost all vertical levels, while trends for relative humidity were mostly statistically insignificant.