diff --git a/config/evaluate/eval_config_diffusion.yml b/config/evaluate/eval_config_diffusion.yml
index 15a567af2..bb55bf133 100644
--- a/config/evaluate/eval_config_diffusion.yml
+++ b/config/evaluate/eval_config_diffusion.yml
@@ -18,14 +18,14 @@
 #      vmax: 40
 
 evaluation:
-  metrics  : ["rmse", "mae"]
-  regions: ["global", "nhem"]
+  metrics  : ["rmse", "mae", "spread", "ssr","ssr_adj", "crps"] #spread + ssr are ensemble (probabilistic) metrics
+  regions: ["global"]
   summary_plots : true
   ratio_plots : false
   heat_maps : false
   summary_dir: "./plots/"
   plot_ensemble: "members" #supported: false, "std", "minmax", "members"
-  plot_score_maps: false #plot scores on a 2D maps. it slows down score computation 
+  plot_score_maps: true #plot scores on a 2D maps (incl. ensemble spread map). it slows down score computation
   print_summary: false #print out score values on screen. it can be verbose
   log_scale: false
   add_grid: false
diff --git a/packages/evaluate/src/weathergen/evaluate/plotting/line_plots.py b/packages/evaluate/src/weathergen/evaluate/plotting/line_plots.py
index 1f99a3728..e11f52d1d 100644
--- a/packages/evaluate/src/weathergen/evaluate/plotting/line_plots.py
+++ b/packages/evaluate/src/weathergen/evaluate/plotting/line_plots.py
@@ -256,6 +256,7 @@ def plot(
         print_summary: bool = False,
         title: str | None = None,
         colors: list[str | None] | None = None,
+        line: float | None = None,
     ) -> None:
         """
         Plot a line graph comparing multiple datasets.
@@ -274,6 +275,9 @@ def plot(
             Name of the dimension to be used for the y-axis.
         print_summary:
             If True, print a summary of the values from the graph.
+        line:
+            If provided, draw a horizontal reference line at the given y-value
+            (e.g. the optimal value of a metric).
         Returns
         -------
             None
@@ -321,7 +325,9 @@ def plot(
         # TODO: generalise this for other x_dims by introducing a "units"
         # entry in the function if needed
         xunits = "hr" if x_dim == "lead_time" else None
-        self._plot_base(fig, name, x_dim, y_dim, print_summary, xunits=xunits, title=title)
+        self._plot_base(
+            fig, name, x_dim, y_dim, print_summary, line=line, xunits=xunits, title=title
+        )
 
     def _plot_base(
         self,
diff --git a/packages/evaluate/src/weathergen/evaluate/plotting/plot_orchestration.py b/packages/evaluate/src/weathergen/evaluate/plotting/plot_orchestration.py
index f32056e47..4ded7b0d3 100644
--- a/packages/evaluate/src/weathergen/evaluate/plotting/plot_orchestration.py
+++ b/packages/evaluate/src/weathergen/evaluate/plotting/plot_orchestration.py
@@ -177,6 +177,8 @@ def _plot_score_maps_per_stream(
     if not valid:
         return
 
+    ens_metrics = {m for m, r in valid if "ens" in r.dims}
+
     plot_metrics = xr.concat(
         [r for _, r in valid],
         dim="metric",
@@ -189,14 +191,15 @@ def _plot_score_maps_per_stream(
         metric=[m for m, _ in valid],
     ).compute()
 
-    if "ens" in preds.dims:
-        plot_metrics["ens"] = preds.ens
+    if "ens" in plot_metrics.dims:
+        plot_metrics = plot_metrics.assign_coords(ens=preds.ens.values)
 
-    has_ens = "ens" in plot_metrics.coords
-    ens_values = plot_metrics.coords["ens"].values if has_ens else [None]
+    all_ens = plot_metrics.coords["ens"].values if "ens" in plot_metrics.dims else [None]
 
     plot_tasks: list[dict] = []
     for metric in plot_metrics.coords["metric"].values:
+        metric_has_ens = str(metric) in ens_metrics and "ens" in plot_metrics.dims
+        ens_values = all_ens if metric_has_ens else [None]
         for ens_val in ens_values:
             tag = f"score_maps_{metric}_fstep_{fstep}" + (
                 f"_ens_{ens_val}" if ens_val is not None else ""
@@ -205,7 +208,10 @@ def _plot_score_maps_per_stream(
                 sel = {"metric": metric, "channel": channel}
                 if ens_val is not None:
                     sel["ens"] = ens_val
-                data = plot_metrics.sel(**sel).squeeze()
+                data = plot_metrics.sel(**sel)
+                if ens_val is None and "ens" in data.dims:
+                    data = data.isel(ens=0, drop=True)
+                data = data.squeeze()
                 title = f"{metric} - {channel}: fstep {fstep}" + (
                     f", ens {ens_val}" if ens_val is not None else ""
                 )
diff --git a/packages/evaluate/src/weathergen/evaluate/plotting/plot_utils.py b/packages/evaluate/src/weathergen/evaluate/plotting/plot_utils.py
index dfb2b3e8f..c9f4052a4 100644
--- a/packages/evaluate/src/weathergen/evaluate/plotting/plot_utils.py
+++ b/packages/evaluate/src/weathergen/evaluate/plotting/plot_utils.py
@@ -390,6 +390,9 @@ def plot_metric_region(
 
                 title = f"{metric.upper()} | {stream} | {ch}"
 
+                ref_line_dict = {"ssr_adj": 1.0}
+                line = ref_line_dict.get(metric)
+
                 plotter.plot(
                     selected_data,
                     labels,
@@ -399,6 +402,7 @@ def plot_metric_region(
                     print_summary=print_summary,
                     title=title,
                     colors=colors,
+                    line=line,
                 )
 
 
diff --git a/packages/evaluate/src/weathergen/evaluate/scores/score.py b/packages/evaluate/src/weathergen/evaluate/scores/score.py
index 6f8faafc7..cdadf0e8e 100755
--- a/packages/evaluate/src/weathergen/evaluate/scores/score.py
+++ b/packages/evaluate/src/weathergen/evaluate/scores/score.py
@@ -199,9 +199,11 @@ def __init__(
         }
         self.prob_metrics_dict = {
             "ssr": self.calc_ssr,
+            "ssr_adj": self.calc_ssr_adj,
             "crps": self.calc_crps,
             "rank_histogram": self.calc_rank_histogram,
             "spread": self.calc_spread,
+            "spread_adj": self.calc_spread_adj,
         }
 
     def get_score(
@@ -254,12 +256,15 @@ def get_score(
             f = self.det_metrics_dict[score_name]
             _logger.debug(f"Using deterministic metric: {score_name}")
         elif score_name in self.prob_metrics_dict.keys():
-            assert self.ens_dim in data.prediction.dims, (
-                f"Probablistic score {score_name} chosen, but ensemble dimension {self.ens_dim} "
-                "not found in prediction data. Skipping score calculation."
-            )
-            return None
+            if self._ens_dim not in data.prediction.dims:
+                _logger.warning(
+                    f"Probabilistic score '{score_name}' chosen, but ensemble dimension "
+                    f"'{self._ens_dim}' not found in prediction data dims "
+                    f"{data.prediction.dims}. Skipping score calculation."
+                )
+                return None
             f = self.prob_metrics_dict[score_name]
+            _logger.debug(f"Using probabilistic metric: {score_name}")
         else:
             raise ValueError(
                 f"Unknown score chosen. Supported scores: {
@@ -1258,6 +1263,33 @@ def calc_spread(self, p: xr.DataArray, **kwargs) -> xr.DataArray:
 
         return self._mean(np.sqrt(ens_std**2))
 
+    def calc_spread_adj(self, p: xr.DataArray, **kwargs) -> xr.DataArray:
+        """
+        Calculate the (unbiased) ensemble spread following the GenCast convention.
+
+        Defined as the square root of the mean *unbiased* (``ddof=1``) ensemble variance, matching
+        the spread of GenCast (Price et al., https://arxiv.org/pdf/2312.15796, Eq. A.6). The
+        finite-ensemble inflation factor ``sqrt((M + 1) / M)`` is *not* applied here; following
+        GenCast it is applied in the spread-skill ratio instead (see ``calc_ssr_adj``).
+
+        Unlike the unadjusted ``calc_spread`` (which uses the biased ``ddof=0`` standard
+        deviation), this uses the unbiased variance, as required for the GenCast spread-skill
+        relation to hold. The unadjusted ``calc_spread`` is left unchanged.
+
+        Parameters
+        ----------
+        p: xr.DataArray
+            Forecast data array with ensemble dimension
+
+        Returns
+        -------
+        xr.DataArray
+            Unbiased ensemble spread (GenCast convention)
+        """
+        ens_var = p.var(dim=self._ens_dim, ddof=1)
+
+        return np.sqrt(self._mean(ens_var))
+
     def calc_ssr(self, p: xr.DataArray, gt: xr.DataArray) -> xr.DataArray:
         """
         Calculate the Spread-Skill Ratio (SSR) of the forecast ensemble data w.r.t. reference data
@@ -1273,10 +1305,44 @@ def calc_ssr(self, p: xr.DataArray, gt: xr.DataArray) -> xr.DataArray:
         xr.DataArray
             Spread-Skill Ratio (SSR)
         """
-        ssr = self.calc_spread(p) / self.calc_rmse(p, gt)  # spread/rmse
+        ens_mean = p.mean(dim=self._ens_dim)
+        ssr = self.calc_spread(p) / self.calc_rmse(ens_mean, gt)
 
         return ssr
 
+    def calc_ssr_adj(self, p: xr.DataArray, gt: xr.DataArray) -> xr.DataArray:
+        """
+        Calculate the ensemble-size-adjusted Spread-Skill Ratio (SSR) of the forecast ensemble
+        data w.r.t. reference data.
+
+        Following GenCast (Price et al., https://arxiv.org/pdf/2312.15796, Eq. A.9), this is
+
+            SSR_adj = sqrt((M + 1) / M) * spread / RMSE(ensemble_mean)
+
+        where ``spread`` is the unbiased ensemble spread (``calc_spread_adj``) and M is the
+        ensemble size. For a perfectly reliable ensemble of finite size M, the RMSE of the
+        ensemble mean is inflated relative to the spread by exactly ``sqrt((M + 1) / M)``
+        (Fortin et al., 2014), so the ``sqrt((M + 1) / M)`` factor applied here makes a perfectly
+        calibrated ensemble yield an adjusted SSR of exactly 1. The original ``calc_spread`` /
+        ``calc_ssr`` are left unchanged.
+
+        Parameters
+        ----------
+        p: xr.DataArray
+            Forecast data array with ensemble dimension
+        gt: xr.DataArray
+            Ground truth data array
+        Returns
+        -------
+        xr.DataArray
+            Ensemble-size-adjusted Spread-Skill Ratio (SSR). Optimal value is 1.
+        """
+        ens_size = p.sizes[self._ens_dim]
+        correction = np.sqrt((ens_size + 1) / ens_size)
+        ens_mean = p.mean(dim=self._ens_dim)
+
+        return correction * self.calc_spread_adj(p) / self.calc_rmse(ens_mean, gt)
+
     def calc_crps(
         self,
         p: xr.DataArray,
diff --git a/src/weathergen/model/diffusion.py b/src/weathergen/model/diffusion.py
index d5f971b2f..473748712 100644
--- a/src/weathergen/model/diffusion.py
+++ b/src/weathergen/model/diffusion.py
@@ -70,10 +70,10 @@ def __init__(self, cf: Config, num_healpix_cells: int, forecast_engine: Forecast
             f"'{self.conditioning}' (got offset={_offset})"
         )
         _input_num_steps = self.cf.get("training_config", {}).get("model_input", {}).get("forecasting", {}).get("num_steps_input", 0)
-        # assert self.conditioning != "forecast" or _input_num_steps == 2, (
-        #     f"forecast.input_num_steps must be 2 when fe_diffusion_model_conditioning is "
-        #     f"'{self.conditioning}' (got input_num_steps={_input_num_steps})"
-        # )
+        assert self.conditioning != "forecast" or _input_num_steps == 2, (
+            f"forecast.input_num_steps must be 2 when fe_diffusion_model_conditioning is "
+            f"'{self.conditioning}' (got input_num_steps={_input_num_steps})"
+        )
         assert self.conditioning not in ["date_time", "date", "time"] or _input_num_steps == 1, (
             f"forecast.input_num_steps must be 1 when fe_diffusion_model_conditioning is "
             f"'{self.conditioning}' (got input_num_steps={_input_num_steps})"