diff --git a/docs/source/chgres_cube.rst b/docs/source/chgres_cube.rst
index 7d3c9f3c1..f32e3a241 100644
--- a/docs/source/chgres_cube.rst
+++ b/docs/source/chgres_cube.rst
@@ -417,6 +417,8 @@ Column 1: Name the code searches for in the table. Do not change.  Some definiti
       * hice - sea/lake ice thickness
       * weasd - snow liquid equivalent
       * snod - physical snow depth
+      ---Optional---
+      * massden - smoke mass mixing ratio (only available in RAP/HRRR-Smoke)
 
 Column 2: Name of the variable in the output “coldstart” files. Unimplemented.