Monthly averages of temperature, precipitation and pressure values from ground-based measurements for long-term data observed in different geographical regions in Turkey have been investigated. The main purpose of this study is to define the role of small-and lar ge-scale phenomena (local and synoptic fluctuations) on precipitation, pressure and temperature variations and their periods. Hence, the Fourier transformation analysis of the monthly average value of meteorological parameters has been considered, and phase angles and amplitudes have been calculated. The first-order harmonics of temperature, :precipitation and pressure values show large-scale effects, while higher-or der harmonics show the effects of small-scale variations. The variations of first-sixth-order harmonic amplitudes and phases provide a useful means of understanding the la ge-and local-scale effects on meteorological parameters. The phase angle can be used to determine the time of the year when the maximum or minimum of a given harmonic occurs. The analysis helps us distinguish different precipitation, pressure and temperature regimes and transition regions. Local-and large-scale phenomena and some unusual seasonal patterns ape also defined. This analysis also shows strong annual variations of precipitation in the Southern and Western part of Anatolia and that strong semi-annual fluctuations are predominant in the eastern part of Turkey. Strong annual influence on pressure variations is mostly observed in the coastal part of Turkey. The dominance of the first three harmonics of pressure is smaller over most of the terrestrial stations. Temperature variations are mostly influenced by the annual fluctuations in eastern and south-eastern Anatolia. The urban heat island caused by developing metropolitan areas refers to local warming effects and heat islands. The local effects are observed in the western part of Turkey.