Diagnostic analysis is performed to study the characteristics and causes of snow cover in an extreme snowstorm process over Shandong from 13 to 15 December 2023 by using routine observation data, hourly intensive observation data of snow depth, and ECMWF (European Centre for Medium-Range Weather Forecasts) Reanalysis v5 (ERA5). The results are as follows. (1) This snowstorm is caused by a Jianghuai cyclone with the characteristics of long duration, complex precipitation phase, low basic temperature, large cooling range, and thick snow depth. (2) The maximum newly increased hourly snow depth is 8 cm; the average SLR (snow-to-liquid ratio) in Shandong is 0.7 cm·mm^-1, exhibiting a pattern of larger snowfall amount in the western region and smaller anount in the eastern region. (3) For the meteorological stations with snow cover, the 2-m temperature and snow surface temperature show a downward trend from the beginning of snowfall to the forming of snow cover; the 0-cm ground temperature drops in the early stage of snowfall, but no longer changes significantly after the forming of snow cover. For the meteorological stations without snow cover, the characteristics of the near-surface temperature can be divided into 4 conditions during the whole snowfall period. (4) The SLR changes obviously with the 2-m temperature, while the ground temperature has little effect on the SLR after the forming of snow cover. The SLR rises as the snow surface temperature decreases when the SLR is below 0.75 cm·mm^-1; however, when the SLR exceeds 0.76 cm·mm^-1, the snow surface temperature no longer shows significant changes.