Abstract: Late spring frost is one of the major compound climate–phenological hazards affecting apple orchards in mountainous regions of Iran, with damage resulting primarily from the coincidence of temperature drops with sensitive phenological stages, particularly flowering. This study aimed to analyze the atmospheric circulation patterns associated with late spring frost and investigate major frost events in 2002, 2006, and 2013 in Semirom County, Iran. Daily minimum air temperature recorded at the Semirom synoptic station was examined over 2002–2021 during the sensitive phenological window for apple trees, from 4 April to 27 April. For the selected events, minimum, maximum, and mean air temperature, precipitation, relative humidity, and wind speed were extracted for the synoptic window of 1–19 April. In addition, NCEP/NCAR reanalysis data at different atmospheric levels were analyzed using GrADS version 2.1 to identify the underlying synoptic mechanisms. Of the 480 days examined, 473 had valid observations, including 62 days classified as weak frost and 31 days as moderate frost; no severe frost days were detected. The lowest recorded temperature was −1.5 °C, while minimum temperatures during the 2002, 2006, and 2013 events were −1.0, −0.4, and −0.6 °C, respectively, placing all three events in the moderate category. Nevertheless, the greater damage reported in 2013 was associated with the coincidence of cold conditions and the flowering stage. Synoptic analysis of all three events revealed the advection of cold air from higher latitudes and the establishment of a mid-tropospheric trough. The occurrence of precipitation concurrent with the temperature minimum in 2006 and 2013 further indicated the contribution of advective processes alongside radiative cooling. The results demonstrate that frost damage in Semirom is not directly determined by the absolute minimum air temperature at the station but rather by the interaction between atmospheric conditions and crop phenology. Integrating long-term statistical assessment with event-based synoptic analysis can therefore provide a more robust basis for frost-risk assessment and the development of early-warning systems for apple orchards in Semirom.