diff --git a/lib/xmet/skew_t.py b/lib/xmet/skew_t.py
index 0bb85ea..5fd9bce 100644
--- a/lib/xmet/skew_t.py
+++ b/lib/xmet/skew_t.py
@@ -20,6 +20,9 @@ TEMP_CENTER     =   0 # degrees C
 TEMP_STEP       =   5
 TEMP_STEP_COUNT = math.ceil(TEMP_RANGE / TEMP_STEP)
 
+LAPSE_RATE_DRY   = 9.8 / 1000 # degrees C per 1000m
+LAPSE_RATE_MOIST = 4.0 / 1000
+
 def clamp(value, lowest, highest):
     if value < lowest:
         return lowest