The Seasonal Displacement of the Beginning and End of Jordan’s Rainy Season

      This study was conducted to explore the nature and the patterns of fluctuations in the beginning and end of the rainy seasons in Jordan. The study also aimed at determining if there was any real offset of the early rainy period which had normally extended over the months of October and November, as well as the late rainy period, which had normally lasted till May.  Besides, the study aimed at exploring possible overall spatial climatic causes that may be lurking behind the offset of the typical annual dates for the beginning and end of rainfall periods, as this type of information is of significant importance to most economic activities, particularly the agricultural sector.
       To achieve the aims of this study, the researchers analyzed quantities of the monthly rainfall collected at the metrological station at Amman Civil Airport over the period from 1922 to 2007, since this station is the oldest weather station in Jordan.  It Covers eighty-five years, and it is centrally located among the various geographical regions of the Kingdom.
       To explore the patterns that were expected to emerge from the data, rain quantities were collected throughout the month of October using the Step wise regression procedure,  as this month represents the beginning of the early rainy season.  Furthermore, a similar statistical analysis was performed for the quantities of the rain collected in May as it represents the end of the late rainy season.
      The results of the study indicate that there were three patterns in the early rainy period which had witnessed a decrease in the rainfall, while there were three patterns in the late rainy period which had witnessed an increase in the rainfall.
Key Words: The Rainy Season, Step-wise Regression, Seasonal Offset, Rain-fall patterns, area of High Pressure