Time change in airflow structures in isolated snow clouds over the Sea of Japan was investigated by means of dual-Doppler radar observations. Rawinsonde and dropsonde observations were also carried out to support the Doppler radar observations. Isolated snow clouds were observed in a late stage of an outbreak of winter monsoon and had a lifetime of about 1 hour. The sonde observations showed that these clouds were formed in a convectively unstable layer with a weak vertical wind shear. The Doppler radar observations demonstrated that the airflow patterns inside the clouds varied with time. In the developing stage, updrafts dominated in the clouds with slight downdrafts. In the mature stage, updraft and downdraft were comparable in area. In the decaying stage, downdraft was dominant in the clouds. The updraft and downdraft existed in the forward and rearward portion with respect to the cloud movement, respectively. The magnitude of updrafts was at most 2 ms^-1 in the developing and mature stages, and had smaller values in decaying stage. A conceptual model of airflow structures is proposed based on the results of the observations.