Abstract: The spatial synoptic classification (SSC) is modified by taking seed days within sliding periods so that seed days are selected from the warmest and coldest periods of the year and two intermediate periods. Artificial seed days are produced to represent typical weather patterns on other days of the year. From the selected seed days and the artificial seed days, a classification technique is developed to categorize a weather type for any day. Once the seed days are selected for a weather station, those seed days can be used to select seed days for nearby weather stations.