diff --git a/mlair/data_handler/default_data_handler.py b/mlair/data_handler/default_data_handler.py
index 22a8ca4150c46ad1ce9ba0d005fa643e27906f53..8ad3e1e7ff583bd511d6311f2ab9de886f440fc9 100644
--- a/mlair/data_handler/default_data_handler.py
+++ b/mlair/data_handler/default_data_handler.py
@@ -215,32 +215,29 @@ class DefaultDataHandler(AbstractDataHandler):
                 raise TypeError(f"Elements of list extreme_values have to be {number.__args__}, but at least element "
                                 f"{i} is type {type(i)}")
 
+        extremes_X, extremes_Y = None, None
         for extr_val in sorted(extreme_values):
             # check if some extreme values are already extracted
-            if (self._X_extreme is None) or (self._Y_extreme is None):
-                X = self._X
-                Y = self._Y
+            if (extremes_X is None) or (extremes_Y is None):
+                X, Y = self._X, self._Y
+                extremes_X, extremes_Y = X, Y
             else:  # one extr value iteration is done already: self.extremes_label is NOT None...
-                X = self._X_extreme
-                Y = self._Y_extreme
+                X, Y = self._X_extreme, self._Y_extreme
 
             # extract extremes based on occurrence in labels
             other_dims = remove_items(list(Y.dims), dim)
             if extremes_on_right_tail_only:
-                extreme_idx = (Y > extr_val).any(dim=other_dims)
+                extreme_idx = (extremes_Y > extr_val).any(dim=other_dims)
             else:
-                extreme_idx = xr.concat([(Y < -extr_val).any(dim=other_dims[0]),
-                                           (Y > extr_val).any(dim=other_dims[0])],
+                extreme_idx = xr.concat([(extremes_Y < -extr_val).any(dim=other_dims[0]),
+                                           (extremes_Y > extr_val).any(dim=other_dims[0])],
                                           dim=other_dims[0]).any(dim=other_dims[0])
 
             sel = extreme_idx[extreme_idx].coords[dim].values
-            extremes_X = list(map(lambda x: x.sel(**{dim: sel}), X))
+            extremes_X = list(map(lambda x: x.sel(**{dim: sel}), extremes_X))
             self._add_timedelta(extremes_X, dim, timedelta)
-            # extremes_X = list(map(lambda x: x.coords[dim].values + np.timedelta64(*timedelta), extremes_X))
-
-            extremes_Y = Y.sel(**{dim: extreme_idx})
-            #extremes_Y.coords[dim].values += np.timedelta64(*timedelta)
-            self._add_timedelta(extremes_Y, dim, timedelta)
+            extremes_Y = extremes_Y.sel(**{dim: extreme_idx})
+            self._add_timedelta([extremes_Y], dim, timedelta)
 
             self._Y_extreme = xr.concat([Y, extremes_Y], dim=dim)
             self._X_extreme = list(map(lambda x1, x2: xr.concat([x1, x2], dim=dim), X, extremes_X))