Abstract Twice-daily synoptic analyses are statistically analyzed for a sample of nine individual winters. Temporal variance and covariance quantities at each individual grid point are partitioned into “low-pass” (approximately 10–90 day) and “band-pass” (approximately 2.5–6 day) components by means of conventional filtering procedures. The time-filtered variance and covariance fields are displayed in terms of hemisphere maps. Included in the analysis are sea level pressure, 300 mb height, 500 mb wind statistics, and 850 mb temperature and poleward heat flux. The most definitive results of the study involve the “band-pass” fluctuations which appear to be associated with developing baroclinic waves. The fields of band-pass 1000, 50 and 300 mb geopotential height, as well as the 500 mb meridional wind component and relative vorticity all exhibit elongated variance maxima coincident with the two major Northern Hemisphere storm tracks, which lie downstream and somewhat poleward of the cores of the Asian and N...