Abstract: Many papers show that the rhytms take an important part in long-range weather forecasting. The rhythms appear in wide band of spectrum varying, from two months to eleven months, but the most dominant is the half year rhythm. Investigations on the development of similarities between two monthly mean circulation maps in the Northern Hemisphere or between two sea surface temperature maps in North Pacific and North Atlantic proved the realities of the rhythm activities. For example, if the sea surface temperature anomalies are similar for two months in spring or summer, then they usually get some similarity in both following autumn or winter. Atmospheric circulation anomalies in summer are formed under the influence of atmospheric circulation anomalies in the past three and four seasons. Two kinds of mechanism controlling rhythms were proposed. The first, summer sea surface temperature in the westerly drift current in the North Pacific can give some influence on the winter sea surface temperature, and then on the atmospheric circulation and weather. The second, both sea surface temperature and atmospheric circulation in the low latitudes at east part of North Pacific in winter act as forcing factors to the atmospheric circulation in the following summer.