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300 hPa European Blocking Index (experimental)

Past 100 Days by pentad (5-day average)

High (Low) Index Values Indicate Anomalous Ridging (Zonal Flow)         Data:   NCEP-NCAR reanalysis zonal wind component on a 2.5x 2.5deg. lat/lon grid Base Period for Climatology:  1971-2000  Data Source:  NCEP (National Centers for Environmental Prediction) Description:  The blocking index is based on observations of pentad (5-day average) wind over the region 15W to 25E and 35n to 55N.  If the pentad zonal wind equals the climatological value for that time period, the index is zero.  If the pentad zonal wind is less than average the index is postive, while the opposite is true if the index is negative.  Values close to +/- 1 indicate relatively strong events.