Updates to NMSE notebook / functions

Found a bug in reading the data -- we want to use (base_start_date,
base_end_date) as the date range for the base_case data read, not (start_date,
end_date). Also, for some reason I needed to .load() the data before calling
.rolling() -- it's not clear to me why this was necessary but it avoided an
Exception being raised from that function

nblibrary/atm/Global_PSL_NMSE_compare_obs_lens.ipynb

@@ -204,7 +204,7 @@
     "        fix_time_dim(\n",
     "            xr.open_mfdataset(f\"{base_file_path}/*PSL*.nc\", decode_times=False)\n",
     "        )\n",
-    "        .sel(time=slice(start_date, end_date))\n",
+    "        .sel(time=slice(base_start_date, base_end_date))\n",
     "        .assign_coords({\"lon\": lon, \"lat\": lat})\n",
     "        .PSL\n",
     "        / 100.0\n",

nblibrary/atm/averaging_utils.py

@@ -36,7 +36,10 @@ def seasonal_climatology_weighted(dat):
     datw_am = dat * wgts_am
 
     ds_season = (
-        datw.rolling(min_periods=3, center=True, time=3).sum().dropna("time", how="all")
+        datw.load()
+        .rolling(min_periods=3, center=True, time=3)
+        .sum()
+        .dropna("time", how="all")
     )
     dat_djf = ds_season.where(ds_season.time.dt.month == 1, drop=True).mean("time")
     dat_mam = ds_season.where(ds_season.time.dt.month == 4, drop=True).mean("time")