diff --git a/weatherbench2/config.py b/weatherbench2/config.py
index 13c0969..3be06e9 100644
--- a/weatherbench2/config.py
+++ b/weatherbench2/config.py
@@ -35,6 +35,8 @@ class Selection:
     levels: List of pressure levels.
     lat_slice: Latitude range in degrees.
     lon_slice: Longitude range in degrees.
+    aux_variables: Sequence of auxiliary forecast variables required for certain
+      evaluation metrics.
   """
 
   variables: t.Sequence[str]
@@ -46,6 +48,7 @@ class Selection:
   lon_slice: t.Optional[slice] = dataclasses.field(
       default_factory=lambda: slice(None, None)
   )
+  aux_variables: t.Optional[t.Sequence[str]] = None
 
 
 @dataclasses.dataclass
diff --git a/weatherbench2/evaluation.py b/weatherbench2/evaluation.py
index a93907b..8fea878 100644
--- a/weatherbench2/evaluation.py
+++ b/weatherbench2/evaluation.py
@@ -140,9 +140,14 @@ def _impose_data_selection(
     selection: config.Selection,
     select_time: bool = True,
     time_dim: Optional[str] = None,
+    select_aux: bool = False,
 ) -> xr.Dataset:
   """Returns selection of dataset specified in Selection instance."""
-  dataset = dataset[selection.variables].sel(
+  if select_aux and selection.aux_variables is not None:
+    sel_variables = set(selection.variables) | set(selection.aux_variables)
+  else:
+    sel_variables = selection.variables
+  dataset = dataset[sel_variables].sel(
       latitude=selection.lat_slice,
       longitude=selection.lon_slice,
   )
@@ -314,10 +319,12 @@ def open_forecast_and_truth_datasets(
   )
 
   obs_all_times = _impose_data_selection(
-      obs, data_config.selection, select_time=False
+      obs,
+      data_config.selection,
+      select_time=False,
   )
   forecast_all_times = _impose_data_selection(
-      forecast, data_config.selection, select_time=False
+      forecast, data_config.selection, select_time=False, select_aux=True
   )
 
   if data_config.by_init:  # Will select appropriate chunks later
@@ -328,6 +335,7 @@ def open_forecast_and_truth_datasets(
       forecast,
       data_config.selection,
       time_dim='init_time' if data_config.by_init else 'time',
+      select_aux=True,
   )
 
   # Determine ground truth dataset