diff --git a/fhem/FHEM/UConv.pm b/fhem/FHEM/UConv.pm
index fd0cccd4d..0e1d24fa5 100644
--- a/fhem/FHEM/UConv.pm
+++ b/fhem/FHEM/UConv.pm
@@ -442,6 +442,8 @@ sub values2weathercondition($$$$$) {
         $condition = "cloudy";
     }
 
+    $condition = "nt_" . $condition if ( !$isday );
+
     return $condition;
 }