Based on the analysis of validated satellite data on temperature, salinity, and sea level, the synoptic variability of the characteristics in the area of the River Plums frontal zone of the Kara Sea in August–September 2019 is described. The validation was carried out on the basis of comparing the measurements of the radiometers of the Suomi NPP VIIRS and NASA SMAP satellites with in-situ data from the R/V Professor Levanidov from September 15 to 27, 2019. The results of the validation showed high accuracy of satellite systems reproduction of the surface temperature and salinity fields of the Kara Sea. The position and characteristics of the surface desalinated layer, at the outer boundary of which the River Plums frontal zone is detected, were distinguished using cluster analysis. It was found that the gradients in the frontal zone during the period under review ranged from 0.05 to 0.1 °C/km, and the salinity from 0.08 to 0.13 %/km. The variability of the area and gradients of the River Plums frontal zone in the warm period of the year is shown.