diff --git a/tutorial/Note2_2D_NLDAS2_domain.ipynb b/tutorial/Note2_2D_NLDAS2_domain.ipynb
index 320b4d5..dfea0cf 100644
--- a/tutorial/Note2_2D_NLDAS2_domain.ipynb
+++ b/tutorial/Note2_2D_NLDAS2_domain.ipynb
@@ -132,9 +132,15 @@
     "`perl extract_nldas.perl`\n",
     "\n",
     "\n",
-    "### 3.2 extract the initial-only fields\n",
+    "### 3.2 extract the initial-only fields (Optional, if you want to initialize your model with NLDAS data)\n",
     "\n",
-    "**extract_nldas_init.perl**: extract the initial-only fields (TSOIL,SOILM,AVSFT,CNWAT,WEASD) from the NLDAS GRIB output files\n",
+    "First, you will need to download the initial conditions from NASA NLDAS analysis data, this is different from the forcing data by its filenames `NLDAS_NOAH0125_H*` and variable names, please see this link: \n",
+    "\n",
+    "https://disc.gsfc.nasa.gov/datasets/NLDAS_NOAH0125_H_002/summary?keywords=NLDAS\n",
+    "\n",
+    "You only need the first time step for the initial conditions.\n",
+    "\n",
+    "Run **extract_nldas_init.perl**: extract the initial-only fields (TSOIL,SOILM,AVSFT,CNWAT,WEASD) from the NLDAS GRIB output files\n",
     "\n",
     "Change the date of initialization and run the script one time. The files should appear in the `/extracted_NLDAS_data_path/INIT/` directory.\n",
     "\n",
@@ -295,7 +301,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.9.12"
+   "version": "3.9.13"
   }
  },
  "nbformat": 4,